Conference 7.286::home_work

    I can only answer 2 of the questions, but here goes..
    
    1) It takes my Quasar microwave (700 watts) about 45 minutes to
    defrost 3 pounds of meat.  If I use the "weight defrost" function
    and punch in 3 pounds, it will estimate that it will take about
    30 minutes.  It's estimate is usually not enough.
    
    n) I believe the major factor in a microwave is the wattage.
    The more watts you have, the less time it takes to cook.  Many
    packaged foods have tables that have cooking times versus
    wattage.
    
    Hope this helps,
    jjeff
    

    On my Caloric ME range, which has the microwave right inside the
    electric, self cleaning oven, I believe the max power level is 800
    watts (microwave). In microwave mode, the unit is supposed to boil
    one cup of water in 3 minutes. The manual says that if it doesn't,
    there is something wrong with the microwave. In practice, it seems
    to take about 2 and a quarter minutes.
    
    I suspect you can't translate that directly to your unit (if it's
    800 watts) or linearly if it isn't since the Caloric unit is all
    metal inside, reflecting (almost) all microwave energy either at
    the item to absorb the energy (usually water molecules in the food)
    or into the microwave generator if there's nothing there to absorb
    the energy (thereby burning out the unit). In addition to wattage
    factors, there's the issue of the degree of energy absorption and
    distribution within the units ... and that varies by make and model.

    	1. How long should it take for an average microwave to defrost
    	   a 3 pound steak?

As indicated  in the other notes this time will be dependent on watts,
distribution and design of your particular oven.


    	2. Could the wiring in my house effect the performance of the
    	   microwave?

This is possible but not probable.  Current draw of a microwave is small so
unless you have an arc welder on the same line there is no reason to believe
that you have power delivery problems.


    	3. Are there any devices I could get to measure the effectiveness
    	   of the unit?

The kinds of devices necessary to measure microwave radidation directly
with any kind of accuracy are beyond your means economically.

    	4. Where can I get a good manual on repair and testing of a
    	   microwave?

What kind of testing would you like to perform.  I don't think the average
consumer would have the proper equipment necessary to make the kinds of 
measurements necessary to work on the magnetron.  Other items about the
stove may be possible to troubleshoot.

    	5. Finally, are there any good rules of thumb about how well
    	   a unit should work according to the oven size, type, make,
    	   and wattage?

I doubt it.    

< Note 236.0 by STOWMA::ARDINI "From the third plane." >
                          -< Microwave Oven Checkout >-

The wiring in your house is definitely a factor.  If your microwave can draw
600-700-800 watts of power, you don't want to 'share' the wire with anything
else.  When my father installed his microwave, he cut a new breaker into the
box(600watt Sharp carousel).

I agree with all previous replies regarding, "Your Timing May Vary".  Rarely
do cookbooks agree with the time it really takes to cook an item.  A lot of
this confusion has to do with the fact that the "programmable" microwaves have
their own ideas on how long and how much power is required to cook something,
whereas the cookbook is generally unrelated to your particular unit.
    
Good rules of thumb are hard to come by without experience.  To me, a microwave
is not an "oven".  It is never used in our home to cook anything major like a
roast, turkey dinner, ... they seem to botch meat.  The microwave is awesome at
heating, thawing, fish, vegetables, .... i.e. things that convection ovens
choke on or take a long time to do.  Oven size is usually proportional to
wattage, i.e. a 300watt unit will have a cavity twice as small as a 600watt
unit.  When buying a microwave, I think that 600watts is where to begin unless
you really want an ultra-small counter top unit that will be handy for hot
sandwiches or perhaps thawing.  Programmability is real handy, especially if
your just starting out and don't know the unit or what the appropriate time/
temperature relationship is for a given item.  Make is important, you can get
some low-quality Korean stuff for less, but watch out.  I personnally believe
the Sharp carousel line is superior.  The major reason is the built-in
carousel rather than the "rotating field" units.  The carousel rotates the item
in a CONSTANT field, causing uniform heating on the surface of the item, (assume
a flat surfaced item for sake of argument).  The rotating field attempts to do
the same; however, most don't realize that by rotating the field the beam will
actually disperse causing some of the enery to miss the "target" completely.
Thus, I believe, these machines tend to be less efficient.

Hope this helps.

rep

P.S. When faced with these problems, I ALWAYS refer to the good ole Consumer
     Reports buying guide found in most bookstores for about $5.  If this is
     steep for you, just stop in the store and read the section on microwaves.

    	I want to thank you all for your most informative replies. 
    I ended up calling the GE Consumer hotline and they told me I had
    a Double wave 625 watt Microwave and a good way to test it was to
    boil a cup of ambient temperature water.  It should take 3.5 minutes
    to come to a rolling boil.  It took just short of 4 minutes.  My
    microwave is on a house circuit loaded with stuff so I am a bit
    leary of that part of it.  I'm moving in two weeks so I won't do
    anything about the circuit but will set up a separate line in my
    new local.  Thanks again for all your help.
    
    						Jorge'

    One other thing to consider if you are a novice microwaver is that
    most things cooked in a microwave require standing time.  If you
    try to cook a baked potato the time specified in the cookbook you
    end up with a hard potato unless you give it fifteen minutes or
    so standing time.
    
    Try the cup of water test at several different times of the day
    and see what happens.  My sharp will boil the watter in 2 minutes
    at some times of the day and 4 minutes at other times of the day,
    I guess it depends on what else is running in the house at the same
    time.
    
    Good luck microwaving.
    
    Judie
    
    
    
    

    I have a Tappan Microwave oven (2 yrs. old) that's hurting.
    My wife (following cooking instructions on the food pkg)
    cooked a chicken pie, complete with aluminum pie plate,
    for approx. 1 minute when the unit started buzzing loudly.
    
    She immediately turned it off, however, whenever the oven
    is turned on, it buzzes loudly.  It's not the scatter fan
    (if you just turn the fan on there's no buzzing) - it only
    buzzes when you start cooking something.
    
    Does anybody have a guess as to what is ailing it?
    
    Somebody suggested the "gun" is probably shot - they hinted
    that "the gun" is a major component and would probably cost
    close to a new oven to replace.  
    
    Can anybody suggest where I can get it looked at.  Is a 
    microwave oven a typical DIY project?

    Under no circumstances should you do anything to a microwave oven
    except replace the inside light.   If you do something wrong, you'll
    have to contend with microwave radiation leakage.   I doubt that
    you can even buy the parts.

    My mother-in-law did something similar to our ex-microwave.
    The buzzing sounded just like you describe.
    The repairman said the cyclotron (or whatever it's called these
    days) was gone as were several other parts.  The total bill
    would have almost equalled the cost of a new microwave.  Given
    the choice, I bought a new microwave.  Much nicer then the old
    clunker.  
    
    By the way, many newer microwaves have 10 year warranties on the
    cyclotron.  Mine only had a 5 year warranty and was 6 years old.
    Check your warranty.  
              

    Good advice - .1 and .2.  I'll leave it alone and avoid the 
    leakage.  I'll also check my warranty for the "cyclotron"
    or whatever.  Hopefully, it's beyond the 2 years that the
    product is.
    
    Regards

Unless you guys are bombarding elementary (food) particles , the source of
power for the oven is a Magnetron.(Still a Raytheon trademark?) 

		Happy zapping 
				JP

    Yeah, my wife, of all people, corrected me on that.  I knew it
    ended with a TRON, and somehow CYCLATRON didn't sound quite right.

    I checked my warranty (as suggested) - the unit will be 2 yrs. old
    on Nov.10.  I have a 2 year parts only warranty and 9 yrs. on
    the magnetron.  Looks like I may only be stuck for labor.
    
    Catch 22 will be that labor runs at $30+ per hour with 5 hour
    estimated to replace the magnetron.
    
    Thanks for all the info!

  I read that you shouldn't cook eggs in a microwave oven, but I
tried it because my egg cooker was kaput (see previous note). I
have successfully pre-heated eggs before, but I wanted to see if I
could cook one. I cooked it for 3 minutes at low speed, took it
out, and put it in a pan of water. Ten seconds later it exploded
like a small firecracker and it made an awful mess. So now I know:
Don't cook eggs in the shell in a microwave oven! This also applies
to reheating hard-boiled eggs. It's safer if you peel off the shell,
but that is not foolproof either. A few years ago I tried it and it
blew bits of egg around the oven, even though most of the egg re-
mained whole.

    Eldery lady out west put her cat in the microwave to dry it off
    when it came in wet from a storm. 15 sec on low heat cat-kaboom!
    

    WHAT WILL IT DO TO MY WIFE??????....MMMMMM I WONDER!
    
         I'LL LET YOU KNOW MONDAY!!!

    The cat drying story came from FLORIDA. westerns take better care
    of their animals...
    
    Seriously, the eggs can be cooked in the microwave but the eggs
    must be out of the shells and beaten (ala scrambled eggs). I do
    it all the time.
    
    /cal hoe

    The cat drying story is just another example of modern mythology... It
    has the same veracity as the story about the giant albino alligators
    living in the NYC sewer system.
    
    					andrew

    P.S. I know it's unfeeling, but I find the idea of an exploding egg
         *very* amusing -- sorry :-) 

    I find the idea of the wife in the microwave (re. .2) even more
    amusing!
    
    -- B

Actually, the story I heard was even better.

In the late 40's or early 50's, some engineer in the military realized
that the microwaves they had been using could be employed to heat up
food. After heating up lunches for a while, he realized that there might
be some market potential in the idea.  He talked to his supervisor and
his supervisor suggested that he rig up a demonstration for the general. 

He did.  But (unfortunately) he decided not to use a mundane sandwich 
when there would much more drama in cooking an egg right in the shell.  
And (unfortunately again) he did not think to test out his idea before 
the demonstration in front of the general.

To say the least, the engineer--and the general--ended up with egg in
their faces.  And the use of microwaves for heating up food was set back a
decade or two. 

(I don't know if the story is true, but it sure sounds good!)

Alex

    -1 Could be,while I was going to electronics school @Redstone Arsenal
    in Ala.,some of the guys in Hawk radar school claimed the birds
    flying by the dishes were fried in the process.
    
    	Steve
    

    
    The first thing cooked by microwave was a chocolate bar in the pocket
    of a Raytheon engineer who walked in front of a RADAR.  They then
    sent out for some popcorn and tried cooking that.  The rest is history.
    
    ...don't know if the engineer ever had any children.
           
    

    Navy has been "cooking" turkeys/chickens and hotdogs for years with
    radar; a very graphic safety demo - DO NOT walk in front of a live
    radar...  It's a cute demo, and messy.  And, I'm told, cleaning
    the 'fried' birds off the fantail is not unknown.

    	Also, when using the micro-wave to bake potatoes, be sure to
    puncture the outer skin.  Failure to do this will result in your
    oven looking like someone had just tossed a handgrenade inside it.
    I know.  I had one that the man tried this with.  He bought a new
    oven.
    	You can fry eggs in the microwave, not just scramble them. 
    Just be sure to puncture the yolk with a straw or other object before
    cooking.  If your quick, the yolk doesn't run too far before the
    cooking stops it.

    1.  I have a large Sears (Toshiba?) microwave of unknown wattage.  When
I set the "power" on, say, 50%, I hear the fan or something else go on and off
at various times.  If it's set at 100%, the "noise" is always on.
        a. Do the microwaves fly around  (1) at one constant rate or strength
           (2) for half the time to mimic a 50% rate/strength?
           or
        b. Do the microwaves fly around  (1) at half the rate/strength (2) all
           the time?  If so, what would be the on/off noise I hear?
        (Sorry, microwaves "flying around" is the best I can do.)

    2.  Would a (large) microwave and a refrigerator/freezer on the same
circuit affect the performance of either?  (They're even in the same duplex?
outlet.)

    I think the sound you hear is the fan changing speed when the microwave
    cycles at 50% (I don't know if the mangatron shuts down or goes
    to reduced power though) because of a change in current draw at
    50%. As far as having both the refrigerator and the microwave on
    the same circuit, you'll probably experience some voltage drop because
    of load (or a tripped CB if both drawer max power at the same time).
    A large microwave can draw up to 13 amps (I measured my 1600 watt
    GE) and a refrigerator can be 8-9 amps (varies greatly). It would
    be better to have them on a separate branch circuit.
    
    Eric
    

    ref .1, one other point, if you look in the microwave, you should
    have an ID plate with the wattage (it should be on the unit somewhere).
    Divide it by 120 for the total current the unit will draw. The same
    goes for the refrigerator. A duplex wall outlet is rated generally
    at 15 amps, so if the two figures together are over that, you've
    got a problem.
    
    Eric (some more 2 cents worth)
    

WHen you set the microwave at less than 100%, the magnetron CYCLES on 
and off.  Thus, the current draw has peaks and valleys.  Your 
refrigerator (according to code) should be on a separate circuit, it
also cycles and has peaks and valleys.  The voltage drop caused by one
normally SHOULDN"T hurt the other - but it wouldn't hurt to put a
multitester on it and see how severe it is. 

    The code does NOT require that the refrigerator be on  a separate
    circuit.  Not that it isn't a good idea -- it's just not required.
    
    The code requires two 20 Amp small appliance circits inthe kitchen,
    and that INCLUDES the one that the refrigerator is on.  No lights
    must be on either.   Apart form that, I believe that you can have
    as many other circuits as you want.
    
    At least, that's what I read.  I'f I'm wrong, please tell be, because
    I'm about to add another couple of outlets to my refrigerator circuit.
    
    	Andrew
    

    .-1 is correct, and shows that the code is getting pretty out of
    date since a microwave oven is standard equipment almost everywhere
    now.  Putting a large microwave and a refrigerator on a single 20A
    circuit is running pretty tight on the circuit capacity - if both
    are running any other use of the other outlets on the circuit will
    probably trip the breaker.
    
    And if you put them on separate 20A circuits, then when both are
    running you have nowhere to plug in your 1500W toaster or frypan.

	A magnetron oscillator is the heart of all microwave systems.
	They are able to work at high peak power levels by means of
	a low duty cycle.

	DUTY CYCLE = (Pulse Width)(Pulse Repetition Rate)

	The peak power of a magnetron remains constant over operation.
	The average power of a magnetron is derived this way:

	AVERAGE POWER =  (Duty Cycle)(Peak Power)

	Therefore, by varying the pulse rate (in Hz) or the pulse width
	(in �s) you can vary the average power (in Watts).

	The higher the Duty Cycle, the higher the power and more 
	cooling is necessary to ensure product reliablity.
	

	As for performance effects for your refridgerator I would 
	say no. Microwave ovens are more likely to effect TV's or
	radios but FCC control of emissions and grounding has gotten
	pretty strict over the last 5 years. maybe as the magnetron
	weakens you'll get more spurious harmonics effecting those
	items than you will get from a new one.

	I bought my mother a Litton microwave oven over 15 yrs ago
	and it still cooks like brand new. she uses it everyday.

	bob

Magnatron Oscillation generates heat on the surface of your food, thus
cooking the outside, but the inside is still cooked via conduction, 
as in a normal oven.

Microwaves act on water molecules, which are dipolar in nature, meaning 
they can be aligned in a magnetic field.  What the microwave does is
line all the water molecules up, and then flip polarity... the molecules
flip and the micrwaves flips 'em back.  Does this about 60 times a second,
thus generating heat.

When you put your microwave on 50% power setting, it zaps for a few seconds,
then stops for a few and lets the heat conduct into your food, then zaps
again.  This way, you don't dry out the outside of your roast while the 
inside stays frozen.

re:.0,.7
>Magnatron Oscillation generates heat on the surface of your food, thus
>cooking the outside, but the inside is still cooked via conduction, 
>as in a normal oven.

    Nope.  Microwave oscillation from a magnetron generates heat on
    the inside and out, based upon how penetrable the material is to
    the 2500 MHz waves. 

>Microwaves act on water molecules, which are dipolar in nature, meaning 
>they can be aligned in a magnetic field.  What the microwave does is
>line all the water molecules up, and then flip polarity... the molecules
>flip and the micrwaves flips 'em back.  Does this about 60 times a second,
>thus generating heat.

    Nope.  It does that about 2 billion, 500 million times a second,
    thus generating heat.

>When you put your microwave on 50% power setting, it zaps for a few seconds,
>then stops for a few and lets the heat conduct into your food, then zaps
>again.  This way, you don't dry out the outside of your roast while the 
>inside stays frozen.

    Sorta.  It turn on and off, since the magnetron runs at one level,
    and the lower setting lets the food even its own temperature out,
    not so simple as inside/outside.  Some materials absorb more than
    others, and ovens aren't perfect at spreading around the power.
    And the on/off time is probably in seconds, not fractional seconds.

    RE .7
    	
    	Microwaves do act on water molecules, but excite their vibration
    mode.  Water molecules get 'hot' by having the hydrogen and oxygen
    atoms 'shake' as if they were connected by springs.
    
    				=Ralph=

Re: .8


>    Nope.  Microwave oscillation from a magnetron generates heat on
>    the inside and out, based upon how penetrable the material is to
>    the 2500 MHz waves. 


	If I understand your answer, microwaves heat from the inside out
	AND the inside in? If i put a cold hamburger into my microwave for
	30 seconds, the outside is hot and the inside is *cold*. This implies
	heating from the outside in.

	Your statement about how penetrable the food is makes me think that
	the actual focus of the microwaves is somewhere (not too far) below
	the surface of the food. Is this correct? If so I'd say that it is
	a nit to say that microwaves cook from the inside out.

	Try putting a frozen chicken in your microwave at full power sometime.
	You'll get yucky dried up organic matter covering a chicken popsicle.

Larry

                Actually you're both sorta right. The microwaves shake
        up those atoms that it can reach. How deep that is depends on
        the type of material and its water content. It's sorta like
        light penatrating a fog. A thin fog lets the light get well into
        it, and a thick one barely lets it penatrate. 
                
                /s/     Bob

>    Nope.  Microwave oscillation from a magnetron generates heat on
>    the inside and out, based upon how penetrable the material is to
>    the 2500 MHz waves. 

The heat is generated both at and near the surface, but not deep inside, 
as is common myth.  The microwaves are attenuated (absorbed) as they
penetrate the material and the heating effect decreases rapidly. 
According to the Reference Data for Radio Engineers, "The skin depth is
the that distance below the surface of a conductor where the current
denisty has diminished to 1/e of its value at  the surface"  At several
'skin depths' below the surface there is no microwave heating and
conduction takes over as stated earlier in .7. 

re: < Note 2269.8 by DELNI::GOLDSTEIN "Follow flock, become lampchop" >

Gee... thanks for so nicely pointing out my errors!  Makes me real 
anxious about trying to answer more questions here... what I nice way
to great my very first entry in HOME_WORK!

8^(

For the rest of you, sorry about the error in frequency... but as was
pointed out in later replies, the food does indeed heat from the outside
in, with penetration determined as in the fog example.   (I particularly
liked the "chicken popsickle" one!)  8-)

My atomic theory is a little rusty (braincells have a short half-life, shall 
we say?)... I was under the impression that the whole molecule oscillated,
but the "atoms on a spring" analogy is, in fact, more correct.  (Makes me
think of those false glasses with the eye balls that spring out!) 8-)

I think I'll go back to batch extracts and read only on this one... 
Seems you have to be 110% correct or someone jumps on your sh*t.

	C'mon, Guys.

	I've been trying to resist this, but I just can't:  Isn't this
	topic bcoming a little  --  are you ready?  --  "heated"?
	Ha HA HA!

	Sorry.

	Anyhow, my owner's manual says the microwaves attenuate by about
	1/2 per inch in water.  Presumably it means energy density drops
	off at that rate.

	Does anyone know their attenuation in air?  Do I have to build a
	30' kitchen so I can stand far enough away from my heating coffee
	not to get broiled by a leaking photon?

	Regards, Robert.

    
    
    		How do microwaves work?
    
    	Plug them in, open the door, put the food in, close the door,
    	press 3, press 0, press START, wait 30 seconds, when buzzer goes
    	off, take food out and eat it.  (For the non-technical readers)
    	;-)

    	Phil

    Good grief, Charlie Brown!  I got a lot more than I asked for, MOST of
which has been greatly appreciated  :-)
    Clarification on my second question (.0 was mine) - does a frig and a
microwave being on the same circuit affect the performance of either?
    1  The frig affects the microwave, if at all, only when it cycles on
(power surge?), right?
    2  What else might account for our microwave (large) heating a cup of
water to boiling consistently more slowly than the (small) microwaves here
amongst our offices?

    Microwaves attenuate maybe 1/2 through more air than the depth of
    the atmosphere!  In other words, air doesn't absorb them (at the
    2500 MHz frequency used in ovens) significantly.
    
    Thus, the field strength attenuates inversely to the square of the
    distance (area of a sphere).  Which isn't very fast!
    
    Different foods, of course, have different absorption rates; meat
    does absorb quite quickly so the inside of a roast doesn't heat
    up very quickly.  Breadstuffs (bagels, old rolls, etc.) heat up
    very quickly on the inside. 
    
    WRT a fridge; it's just a matter of sufficient current, but I'd
    advise against it since a fridge can draw quite a lot during starting
    or, perhaps, defrost.
          fred

    A few things in a house should be on their own circuit.
    
    furnace
    refrigerator
    freezer
    sump pump
    
    

    .17 and friends, on appliances that should be on isolated lines:
    
    Some friends are renting a place with a "portable" dishwasher; 
    the hose length restricts them to plugging it into one or two
    outlets, on the line that the countertop microwave uses.  They tell
    me that after tripping the breaker three times in the first month,
    they got used to the idea that only one of the two can be running
    at any given time...
    
    Dick

Re: Portable Dishwasher

We had the same problem. Solved it with a 6' appliance extension cord. 
Now we plug the dishwasher into an outlet that isn't on the refrigerator 
or Microwave circuits.

Only cost a few dollars.

Chuck

    Hi,
    
    My microwave seems dead!!  I go to turn it on and nothing happens.
    No sound, nothing.  Is there a fuse inside the unit perhaps?
    
    What I'm really concerned about is, is this something that should
    be taken apart, can it be done safely?  Are there dangeous components
    inside?  I was about to take it apart last nite but you need the
    6 pointed star screwdrivers to open it up.
    
    
    
    Deciding whether to buy the screwdriver,
    
    
    Jack

    The same thing happened to me.  When I called Sears to find out
    how much it might cost just to have someone see what's wrong, I
    took the thing apart myself and found a blown fuse inside.  I replaced
    it and it's fine (yes, with a same-size fuse and no, I don't care
    why it blew in the first place).
    
    Those drivers (I think they're called Torx or something) are available
    at Somerville Lumber as little bits that you insert into some kind
    of handle.

    RE: .21, that "6 point star screwdriver" is probably a Torx screw.
    You often see them in car trim these days. If nothing happens at
    all, check the obvious first. Is the outlet good? If the unit has
    a digital readout, is that working? When you try to use it, does
    the light inside go on? When you open the door, does the light go
    on? Unless you know something on how it works, you might get into
    more trouble going inside to have a look. Even if you do know what
    you're doing, you should have a leakage test done when you put it
    back together.
    
    Eric

    Thanks for the advice.  No, the display is dead, and so is the light
    bulb.  The outlet is good, c.b. isn't tripped, etc.  I checked the
    obvious but what it boils down to is this 18"X21"X24" useless box
    of electronics taking up space in my kitchen.
    
    I will get a torx driver set and take a look inside.  Hope its the
    fuse.  If I have to disturb any shields or something inside I'll
    have a leakage test done after its back together.  Don't want
    any of that radiation cooking me as it cooks the food.
    
    
    Glowing in Leominster,
    
    
    Jack
    

    There is indeed a fuse.  You reach it from the back on an Amana
    and it is a simple matter to replace.  It cost me big bucks for a service
    call to have a $.69 fuse replaced.  Since the cover formy Amana
    is nowhere near the seal you don't have to worry about "leakage".
    service call the first time it blew.
         
    Check your owner's manual.  Our fuse is nowhere near the seal, so
    there is no worry about "leakage".
   
    Peg
 

This explanation is excellent for the non-technical - knowledge is the 
enemy of fear.

The author, 
Brian Reid is the moderator of alt.gourmand and is acknowledged to be one of
the more knowledgable chefs on the USENET network.
 
This message is an updated reposting of an essay I wrote about microwave
ovens in January 1985. As far as I can tell there has been nearly 100%
turnover of the readership of this newsgroup since then, so it seems
reasonable to repost it.
 
This message explains the situation about metal and microwave in more detail
than you would ever want to know. I offer this up for those of you who have
an amateur interest in science and who like to know how the things around you
work. I don't think you need any training in physics or electrical
engineering to understand this explanation, though I do throw around some EE
words towards the end.
 
A microwave generator is basically a little radio station. A transmitter. It
generates radio waves of a certain frequency. Radio waves are a kind of
electromagnetic radiation. Light, x-rays, infrared heat rays, and TV
station broadcasts are also electromagnetic radiation.
 
Electromagnetic radiation is absorbed by some substances, transmitted by
others, and reflected by yet others. Visible light is reflected by paper and
absorbed by charcoal and transmitted by glass, for example. X-rays are
absorbed by lead, reflected by certain kinds of steel, and transmitted by
wood and biomass. Whether radiation of a given frequency is reflected,
absorbed, or transmitted is determied by the molecular structure of the
substance and the frequency of the radiation.
 
Typically when radiation energy is absorbed, heat is produced in the thing
that does the absorbing. Whenever energy is transmitted or reflected, heat is
not produced. This is why cars that have black interiors get hotter in the
summer than cars that have white interiors. This is a fundamental law of
physics--that energy is conserved. If sunlight shines on black paper, the
energy is converted from electromagnetic (the light itself) to kinetic (the
vibration of the hot molecules of the paper) but no energy is actually lost.
 
Microwave ovens heat food by "broadcasting" electromagnetic energy at a very
carefully chosen frequency. That frequency lies between UHF television and
infrared light. The frequency is chosen so that it exactly matches one of
the natural vibration modes of the water molecule. A natural vibration mode
is a fancy way of saying that something wants to shake at its own speed.
Like a swing. If you put your baby in a swing and push her, you have to push
at the rate that the swing wants to be pushed, and not at the rate that you
want to push, because if you don't, then the swing isn't going to work, and
you will end up punching your baby in the kidneys instead. So we say that
the swing has a natural vibration mode. Water molecules do, too.
 
When the microwaves hit the water molecules, they hit them at exactly the
right intervals, so that each successive microwave pushes the molecule to
shake a little faster, a little harder. This shaking, this vibration, is the
heat. 
 
This is why you can't heat something that is completely dry. If you put a cup
of salt in your microwave and give it a minute at full power, you will find
that the salt gets barely warm. This is because salt molecules have a
different natural vibration frequency than water molecules. They are like a
swing with a much much shorter rope; you have to push a lot more often and
each swing is a lot faster.
 
So microwave ovens heat by latching on to the water molecules and making them
shake, rattle, and roll. And this "latching on" is really giving them a
series of pushes at exactly the right intervals, using a carefully chosen
radio frequency. The wattage of the microwave oven basically determines how
hard they push on each cycle. If you are pushing your baby in a swing you can
get her to swing very high by giving her 25 little pushes, timed properly, or
by giving her 2 or 3 big pushes, also timed properly. The more watts your
microwave has the bigger is each push that it gives the water molecules.
 
Glass, pottery, clay, Corningware, and things like that are all quite
transparent to microwaves. The waves just zip right on through the way that a
flashlight shines through a window. A cup of salt is also pretty transparent
to microwaves. Putting a cup of salt in there for 60 seconds at full power is
just like running it on empty at full power, because the microwaves go right
through the salt without seeing it.
 
A flat sheet of metal reflects microwaves. If you stop for a moment to
consider how your microwave oven is constructed, you will realize that it
has metal walls. If it didn't have metal walls (or at least if it didn't
have walls made out of something that would block microwaves) then the thing
would radiate all over the room. This would be wasteful of power, and would
also subject you and your aforementioned baby to big doses of microwaves. Bad.
 
My own microwave oven has 6 metal walls; it does not have a glass door.
Yours probably has a glass door. If you look carefully at the glass door you
will note that it has a piece of metal attached to it or embedded in it, and
you will notice that the piece of metal has many holes drilled in it. It
turns out (quite a stroke of luck, actually) that the frequency that is
needed to excite water molecules is also a frequency that will be reflected
by a piece of metal with little holes on it. As long as the holes are little
enough the little buggers can't sneak through. The microwaves aren't micro
enough.
 
Now here comes some actual physics. Take a deep breath. Remember how I said
that all electromagnetic radiation is either absorbed, transmitted, or
reflected, and how I just said that water absorbes microwaves (turns 'em
into heat) and that flat sheets of metal reflect microwaves. Well, pieces of
metal that are not flat, that are shaped more like radio antennas, actually
turn out to absorb some microwaves while at the same time reflecting some.
You've all seen 2-way mirrors that absorb some light, reflect some light,
and also transmit some light. Well, a piece of metal that is not a big flat
sheet will absorb some waves and it will reflect some waves. The exact ratio
of how many get absorbed and how many get reflected depends on the exact
geometry of the piece of metal, and it takes a Ph.D. electrical engineer
quite a while to compute those numbers. As a cook you don't care, except to
know that some are reflected and some are absorbed.
 
Microwaves that are reflected will come back to haunt us in a later
paragraph. Let's look at the ones that are absorbed. Remember how I said that
when energy is absorbed it is in fact "conserved", that no energy disappears,
and that electromagnetic energy is usually converted into heat when it is
absorbed. The reason I said "usually" is that for odd-shaped metal objects,
the energy is absorbed not as heat but as electricity. This is just like a
radio antenna (remember I said that a microwave generator is just like a
radio station). The metal object in the microwave oven is acting like a radio
antenna that is 12 inches away from the radio transmitter, and it is getting
a pretty stiff dose of electricity generated in it.
 
If the electricity picked up by the metal object is energetic enough, it will
start sparking around to other metal objects, such as the walls of the
microwave oven. This spectacular home-made lightning storm is actually quite
safe, though I am sure that none of you will have the nerve to believe me and
set up little lightning storms in your microwave ovens to amuse yourselves
late at night.
 
A little tiny bit of the electricity that is picked up by the metal object
will be converted into heat, just because the metal object is not a perfect
conductor of electricity. Sometimes if the voltages are excessive a spark
will jump. The rest of the time a spark does not jump. What happens to the
rest of the electricity? It is re-radiated as microwaves. The metal object,
acting like a radio antenna, also becomes a radio transmitter. This is quite
consistent with everyday experience: if you shine sunlight on a piece of
black paper, it will get very hot; soon it will get hot enough that it starts
to emit radiation in its own right. The radiation that it emits will be
infrared radiation. Well, the fork or TV-dinner lid or metal rack that you
put in your oven is just re-radiating microwaves back into the body of the
oven. The net result is almost exactly the same as if they had been reflected
off of it in the first place, so I could have just told you that they were
reflected, but then there would be no explanation for all the sparks.
 
Let me stop and summarize. I'm almost done with the explanation, but I want
to do a review before I do the conclusion. Microwaves heat by being absorbed.
Water absorbs them. Many other objects do not absorb them. Metal reflects
them, except that sometimes it also sparks because of the unusual way in
which the reflection happens. Microwaves that are absorbed are turned into
heat. Microwaves that are not absorbed are not turned into anything.
 
But wait a minute. Let's say that you turn your microwave oven on for 60
seconds and start pumping the old 750 watts into the chamber, and that the
chamber is empty. Since the chamber is empty, nothing is absorbed. What
happens to those microwaves? Does the box slowly fill up with them? Do they
evaporate?
 
The answer is that I lied to you about the radio station. Well, not exactly
lied. It really is just like a radio station, as long as the radio station
has all of its listeners 12 inches away from the broadcasting antenna. The
situation is really a lot more complicated than an ordinary radio station
because there is a close coupling between the sender and receiver. What
happens to the microwaves mentioned in the previous paragraph is that they
are never gnerated, because there is an impedance mismatch between the
microwave generator and the microwave recipient.
 
I promised I wouldn't mention physics, and here I am talking about impedance
mismatches. Well, once again this is a simple concept. Whenever you are
trying to move energy from one place to another, it is important that the
sender and the receiver are in harmony about the details of this transfer.
Riding a bicycle is a good example. If you are trying to ride in too low a
gear, you can't go very fast because your feet spin around and around and
the bike barely moves. If you are trying to ride in too high a gear, you
also can't go very fast because your legs aren't strong enough to push the
pedals around against that very high gear. But if you are in just the right
gear, you can zoom, and all of that energy gets transferred between your
legs and the bicycle. If you are in "just the right gear", a physicist would
say that there is an impedance match between your legs and the bicycle. If
you are in a gear that is to high or too low, then there is an impedance
mismatch.
 
Electromagnetic energy transfer is kind of like the bicycle example. The
microwave generator is like your legs, and the food that you are trying to
heat is like the bicycle. Some guy at the microwave oven factory chose the
gear, and built it in. If the oven is empty (that is, if the oven contains
nothing that is absorbing the energy) then it is like pedaling in too low a
gear. If the oven is overly full, then it is like pedaling in too high a
gear. If the oven has just the right amount of water in it, then everything
is copacetic, and the water gets heated. The important concept here is that
unless the right amount of water is in the microwave oven, then there is no
energy being transferred out of the microwave generator into anything.
 
Unfortunately, there IS a steady supply of energy going in to the microwave
generator, even when nothing is going out. That steady supply is coming in
over the power cord, 750 watts' worth, and going on in to the magnetron tube
that does the actual microwave generation. If 750 watts are going in and
nothing is coming out, where are all those watts going? Remember
conservation of energy. The answer is that if those 750 watts don't get to
leave the magnetron in the form of microwaves heading for some water, then
they will stay behind and convert themselves into heat. The magnetron just
gets hotter and hotter. Pretty soon you get meltdown. Exactly how soon you
get meltdown depends on the cleverness of the engineers who built your oven.
If they installed lots of ways to get the heat out of your magnetron, then
you can run it empty all day without hurting anything but your electric
bill. If they didn't install very many ways to get the heat out of your
magnetron then you will burn it out.
 
When you turn your microwave oven on you always hear a fan. Pretty loud fan,
too. You never knew it was a fan, did you? You always thought it was just
the noise that microwave ovens make when you turn them on. Well, it's a fan,
and what it is doing is blowing hurricanes of air across the magnetron,
trying to cool it off, to make it harder for you to melt it down.
 
I'm almost done with my little essay. I'm actually done with the physics. I
just want to tie down a couple of loose ends. Let's think back to the
"impedance mismatch" paragraph, and the analogy of bicycles in the wrong
gear. Have you ever noticed that the label on TV dinners always says "when
heating two dinners, please heat one, then remove it and heat the other" ?
Have you ever noticed that if you are using the microwave at work to heat
your sandwich and the guy behind you asks if he can just stick his sandwich
in there too, that in fact neither your sandwich nor his sandwich gets hot?
Well, this is the other end of the impedance mismatch situation. If you put
too much into a microwave oven, then it is heated very inefficiently,
because there is an impedance mismatch. If you put a 22-pound turkey into an
ordinary microwave oven and try to heat it, you will find that it doesn't
get very hot. This is because the microwave oven is in the wrong gear.
Unfortunately, there is no way to shift gears on a microwave oven; they are
built with a fixed output impedance and therefore have a fixed gear.
For fastest service, heat small amounts of food at a time.
 
Oh yes, the word "impedance" is pronounced "imPEEdunce".
 
That's the end. Here is the summary:
 
   * Microwave ovens work by heating water molecules. They are fundamentally
     unable to heat anything but water molecules. 
   * Metal objects reflect microwaves. Some reflect more perfectly than
     others. Imperfect reflection results in electricity being generated
     in the metal object.
   * Sometimes that generated electricity will spark over. This sparking
     is quite harmless.
   * If you run your oven totally empty or totally full you run the
     risk of damaging it unless it is well made. The damage comes
     from overheating the magnetron.
   * The amount of heat that goes into your food, plus the amount of
     heat that goes into your magnetron, is a constant. If the food is
     not getting hot, then the magnetron is getting hot.
   * Tell the guy behind you in the cafeteria line, the one who wants
     to put his sandwich in with yours, that you can't let him do it because
     it would cause an impedance mismatch. He will immediately
     decide that you are a kook and he will leave to let you heat your
     sandwich in peace.
 
 
------- End of Forwarded Message

    Thanks for sharing that with us Jeff...
    
    
    
    veeery........interrresting....
    
    
    

    
    	Yes, very interesting.  One question though.  Why are you
    	suppose to wait five seconds before opening the door.  Is
    	that because of the reflected waves, or just an old wives
    	tale?

    
<    	Yes, very interesting.  One question though.  Why are you
<    	suppose to wait five seconds before opening the door.  Is
<    	that because of the reflected waves, or just an old wives
<    	tale?

	No, its to allow all the water molecules to cool down after jumping
	around.  Didn't you listen to your aerobics instructor? :-)

Do you know whether your micro-wave oven needs a turntable or
does it have a micro-wave stirrer (like a slow fan) so that the
micro waves are cooking evenly? I saw a gadget that may cost $3
to make and is great to check out your microwave oven.

You'll need 6 (minium) NE2H neon bulbs (Radio Shack 272-1102) and
a plastic or paper plate. Cut off the leads from the 6 NE2H
bulbs, arrange the bulbs on the edge of the plate in a six-point
star. Glue the bulbs with hot melt, contact or epoxy in place.

Place the plate with the bulbs in the microwave oven. Run the
oven on it's low setting; the bulbs will flash when the
microwaves is absorbed by the neon gas in the bulbs. The pattern
of bulbs flashing will give you an idea of how the microwave
distribution pattern is. On our Litton max sized oven, the bulbs
flashed evenly; on my mom's older Penny's (GE), the bulbs flashed
on one side. You will also see that the power levels are cycled
or actually reduced to give you the power control.

Caution: The bulbs will burn out (blacken) if you leave them on
for more than a minute or run them at maximum power.

cal hoe 

All microwave ovens have a stirrer fan, rotating element, or built-in 
turntable.  The ones with the stirrer fan have a round depression in 
the center of the top of the inside of the oven.  I think only Amana 
makes one with a rotating element.  Thus, you never 'need' an outboard
turntable.  However, the stirrer fan models set up random interference 
patterns, creating hot/cold spots around the oven that vary with the 
shape of the food, thus a turntable is a welcome addition to a 
stirrer-fan-type oven.   Turntable-only ovens have a more predictable 
bullseye pattern, hotter towards the outside.  Great for hot dogs, bad 
for Pizza.

Hello,

I have a very old (circa 1976) Tappan microwave oven.  It has a orange
flourescent-type digital readout and a glass control panel with touch pads.
It is a fairly large oven and has worked flawlessly since I've owned it.

Lately, an intermittent problem has shown up: after programming the oven to
cook, it will start, and one or two seconds after the tube comes on (you hear a
slight vibration while it is cooking, which it has done since new) it will stop
cooking, and the control panel displays all "8"'s.  It behaves then like it had
been unplugged and plugged in again, i.e., it loses the current program and also
the time of day.

I've opened up the oven to check for obvious problems and discovered that a
schematic was included inside.  Other than the control board, the circuit is
fairly simple so I believe the trouble is in the board itself, which is listed
as a separate part.  The board contains a microprocessor and support circuitry
for the flourescent readout and touch switches.  It connects to the rest of the
oven through one simple card edge connector.

I've called a Tappan parts distributor in W. Roxbury (Astro Dist.) and they
informed me that a replacement board would be over $250.00!

I'm wondering if anyone knows where I may be able to get a used board, say, from
an oven whose magnetron tube went bad.

My thanks for any help/suggestions offered.

    
    Just a shot in the dark...
    
    Try unplugging the circuit board and cleaning the contacts with
    an eraser (ie on the back of a pencil).  Some spray-on electrical
    contact cleaner may work also.  Be carefull not to damage the contacts
    with too much erasing, just gently rub them.
    
    I'm guessing that the large current surge (when the unit turns on)
    may cause some inductive and resistive voltage drops within the
    control board, if the voltage drop gets too large, the microprocessor's
    memory could get wiped out.  There may not be anything you can do
    about the inductive loss, but cleaning the contacts may help the
    resistive loss.

    A few of these replies have mentioned leakage tests for microwave
    ovens.  How is a leakage test performed?
    
    Thanks.
    

>< Note 2269.30 by DNEAST::OSULLIVAN_KE >
>                              -< Leakage test... >-
>
>    A few of these replies have mentioned leakage tests for microwave
>    ovens.  How is a leakage test performed?
>    
>    Thanks.

	Assuming the oven hasn't been dropped while moving it or the
       door sprung, the leakage test is done by passing a detector
       around the door edge while the unit is on. The detector can be
       either a small hand-held meter with red and green areas on the
       face indicating a pass/fail situation or a neon bulb encased in
       plastic. If the lamp lights, then there are goodly amounts of
       microwave energy leaking past the door gaskets.

       When the first units became commercially available, they used an
       RFI gasket of fine copper wires woven into a mesh. These were
       very prone to damage and leakage testing was almost mandatory if
       your main concern was safety (microwaves affect pacemakers).
       However, the newer units have an RF trap built into the door that
       is tuned to 'suck up' the energy as it tries to get past the
       vinyl seal. These types of doors are less prone to leakage, as to
       defeat it you would need to physically deform the door enough to
       de-tune the cavity. Unlikely under everyday circumstances.

       From what I can recall, the testers range in price anywhere from
       $5 to $15 depending on type, the neon bulb being the least
       expensive.
       
       Chris
    

    Since this item resides in my home, and I would like to repair it
    myself, I'm going to ask this question here...  Besides, I don't know
    where else to go. :-(
    
    Our micro-wave has started making a "funny buzzin' sound", according to
    my wife.  I took the panel off and it appears that the transformer may
    be going (this is where I think the sound is coming from).  At this
    point, I haven't done any serious testing because there is this
    "mega-capacitor" in the system, that I suspect *could* knock me across
    the room if I touched it off.
    
    Anyway, my question is not so much about the micro-wave as it is about
    the capacitor.  How does one discharge a large capacitor without frying
    your knuckles?  Is there any way to do it with using a large resistor
    (say 20000 ohm, 2 watt)?  I've thought about putting gravy on it and
    letting my neighbor's dog lick it but that probably wouldn't help my
    relationship with my neighbor (not to mention the dog). :-)
    
    Any suggestions about how to discharge the capacitor without having to
    buy any special tools?  How long does it take for a capacitor to
    discharge on its own (or will it)?
    
    Thanks in advance,
    
    +- Mark

I just use an insulated screwdriver on big caps.  Yes, a realy healthy 
one can weld to the screwdriver, but it's not a good bond, and I've 
always been able to pull it free with a snap of the wrist.  

					>>>==>PStJTT

    re:  <<< Note 2948.1 by NSSG::FEINSMITH "I'm the NRA" >>>

    Thanks for the info.  I haven't done much more than listen, so I'm not
    ruling out loose screws.  However, before I go any further, I wanted to
    figure out how to discharge the cap.
    
    +- Mark

If you weld it across the terminals, you're sure it is discharged ;^)

        Thought I would ressurect an old topic with a new entry.
        I have a fairly old microwave (6 or 7 years) that has
        recently developed a problem.  Everything seems to work
        fine except the fuse will blow after about one week's
        use.  The microwave still heats like normal and doesn't
        make any unusual noises.  I have replaced the fuse with a
        type similar to the original (20 Amp slow-blow.)  Any
        suggestions as what might be wrong?  Someone suggested
        that I install a slightly larger fuse, although I would
        think that if things were working properly, the input
        power would not even come close to 2300W (115V x 20A.)  I
        can rule out any electronics being the cause, as the heat
        control and timer use the old fashioned clock motor
        drive.
        
        -Wil

    You can't rule out electronics because of the circuitry that runs
    the magnatron (the device that generates the microwave energy).
    So you you could still have an electronic problem with a component that
    has changed value. Two other possibilities are the cooling fan and
    the scattering blade (don't really know the proper name) drive motors
    binding. Does the oven make any unusual or different noise? The
    amount of power a microwave oven uses is a function of the power
    level and cycle time. 20 amps is a lot of juice (I have a spacesaver
    unit that mounts over the stove where a hood would go, and it only
    draws about 13 amps max), so something is definitely wrong. If I
    remember right, there is a discussion of using (I believe) small
    neon lamps to check if the scatterer is working properly somewhere
    in the Electro_hobby notesfile (this technique displays the pattern
    of microwave energy distribution within the oven). I think you will
    have to have the unit checked out internally.
    
    Eric 

    The reference to using neon bulbs to check out microwave is discussed
    in 2728 in this conference.
    

I think someone may jump all over you for considering using a higher
"amp"ed fuse.  The fuse blows for a good reason.  Say you put in a 25 or 30
amp fuse (I don't even know what's out there).  Chances are the microwave's
plug-in cord is rated at 15 or 20 amps.  Now, "something electronic" goes
wrong with your microwave and it wants more juice.  The fuse says "Sure,
you want 25 amps?  30 amps?  Fine with me."  Meantime, your cord melts. 
And, oh yes, maybe your house burns down.

Any expert concurrence or dismissal?

    I'm no expert, but I'm always happy to share my opinions.
    
    _Temporary_ use of a bigger fuse can be a useful technique for
    debugging purposes, or to limp along (under close supervision) until
    proper repairs can be made.
    
    Using a 30A fuse on an appliance that's plugged into a 20A circuit just
    moves the bottleneck - the circuit's 20A breaker or fuse should protect
    the circuit's wiring and any appliances connected to it.  Moving the
    bottleneck may be just enough to get past a marginal condition in the
    appliance, or to help diagnose that condition.
    
    But indeed, the appliance's designer included a fuse - of a particular
    size - for a purpose, and circumventing that purpose will void your
    warranty, screw up your insurance, rot out your sills, and clog your
    drains.

        Thanks for the suggestions.  I agree that 20 A is lots of
        current and I'll refrain from installing a larger fuse
        for the reasons mentioned.  There is a cooling fan
        mounted just below the magnetron, and it is working fine.
        Also, the wave scattering device consists of a vaned disk
        which rotates at the top of the oven.  It seems to be
        spinning like it should.  
        
        The only electronics involved with the microwave
        generation is a transformer, the magnetron tube, and a
        diode/capacitor rectifier circuit.  I seem to recall
        reading that someone had a microwave that quit working
        and the problem was that the diode opened up.  I would
        think it would a fairly inexpensive item to replace, so I
        might try that and see what happens.  I suppose the
        transformer could have developed some shorted windings,
        but that doesn't seem likely.  
        
        -Wil

    Even though you probably have an electronic problem with the
    microwave, I ran into a problem similar to yours and it turned
    out to be a faulty connection in the molded cord cap. I left the
    unit running and felt the cord cap, it was very warm. I cut it off and
    replaced it with a high quality Hubbel, and no more problem. I really
    don't think this is your problem, but it only takes a minute to
    check. Sometimes a cord, or plug, can break down and contribute to
    the problem when it has been drawing more than its normal operating
    current.
    						Chris

        My latest venture into microwave oven fixing has me even
        more confused.  I got hold of an AC ammeter (actually a
        0.1 ohm resistor with an AC voltmeter connected across
        it), and hooked it up in line with the power cord.  When
        I run the microwave, the current meter indicates about
        12-13A, which obviously shouldn't blow out a 20A
        slow-blow fuse.  I even tried it with several different
        loads (bigger or smaller glasses of water) and the
        current didn't change a bit.  By the way, the water did
        get hot, so the magnetron is doing its thing.  I don't
        know how much input power a microwave should use, but the
        label on the back indicates 115V and 15A, so it would
        appear to be running like it should.  This will be
        replacement fuse #3, so we'll see how long it lasts.
        
        Still puzzled-
        
        Wil

    Sometimes we forget the obvious.
    
    Is it possible the problem isn't the microwave at all?  Maybe you
    have a second appliance on the same circuit that is causing the
    overload, or even just too many 150 watt bulbs?  Or maybe there's
    a spurious short in the house wiring?
    
    Try plugging the microwave into a different 20A outlet, and seeing
    how long it lasts before the fuse goes.
    
       Gary

        RE: .15
        
        Yes, that could be a problem, except the fuse that is
        blowing is inside the microwave itself, rather than in
        the power distribution box.  The only load the fuse
        protects is the microwave circuitry.  So far, the power
        line breaker has never tripped for that circuit.  I think
        it is on a 20 amp line but I'm not sure.  
        
        -Wil

        Just discovered the cause of my fuse blowing in the
        microwave.  The problem turned out to be a loose screw
        holding a safety interlock switch!  On this particular
        oven, there are three switches, two normally open
        switches connected in series with the power line and a
        normally closed switch which is connected across the
        power and ground wires.  When the door is closed, the
        normally closed shorting switch first opens, then the
        series connected switch closes to apply power to the
        magnetron circuitry.  What happened was that the bracket
        holding the normally closed switch came loose and the
        switch was not opening in the correct sequence.  This was
        causing a short circuit through the interlock switches
        and blowing the fuse.  I tightened the screws and now it
        works fine.  Sort of a strange problem, but lots cheaper
        to fix than replacing the magnetron!
        
        -Wil

    I just lost the microwave's heating capacity.  It worked correctly
    in the morning but when I went to warm my lunch, it would not warm
    up at all.
    
    I tried heating up a small cup of water but after nuking for over
    three minutes, the temperature of the water did not change at all.
    
    Everything else seems to be working.  The inside light and the stirrer
    fan comes on, the electronics such as clock and timer are working.
    
    It is GE Spacesaver, over the range type and is already more than
    two years old.  The magnetron is covered for five years but no labour
    or other parts.
    
    Could it be anything else than the mangetron?
    
    Thanks,
    - Vikas

    A friend of mine and I are both having a very similar problem with our
    microwaves.  My problem has a workaround.  What happens is if I plug
    my microwave into one outlet in my kitchen it will start working, but
    will soon just go dead, leaving the "colon" blinking on the timer
    display (no other digits).  It cannot be reset without unplugging the
    power cord and then plugging it in again.  The workaround for me is to
    plug the microwave into another outlet.  The microwave has worked for
    a couple of years in the other outlet.  Any other appliance works just
    fine in the outlet that the microwave doesn't like.  They run off the
    same circuit breaker.  My friend's microwave does the same thing, but on 
    all the power outlets in his house.  He took his to Sears for repair and 
    they changed the magnatron.  Of course, this did not fix the problem.  
    Do microwaves have some kind of ground fault protection circuitry or 
    something that might explain this behavior???  Any ideas appreciated.
    
    					- Vick

    re: .19

    You might want to check and see if the outlet you are having trouble
    with has the wires inserted into "push in" type connections (usually on
    the back of the outlet).  If it does, put the wires on the screw
    terminals.  I have not personally seen this problem, but it's been
    reported here somewhere that the push in connectors do not make a
    really good connection.  You'll have a high resistance connection that
    will show the correct voltage, but hot have the correct amount of
    current capacity.  Since a microwave generally draws a hefty amount of
    current when starting, this could be a problem.

    -Bob                                           

I have a microwave/exhaust-fan-light over my stove.  One day, the microwave
stopped working (while cooking something).  The exhaust-fan and light
also stopped working.  Yet the power outlet it was plugged into was fine.
So I suspect that it is probably caused by a fuse in the unit.

Has anyone encountered this before?
Is it simply a fuse?
Is there any danger opening up a microwave unit?

I have already tried to open it up, but it is not particular easy.
Before I venture further, I thought I would check to see if others had
experiences.  The unit I have is a Whirlpool.

    I have a Sharp microwave with a blown light (light doesn't work any
    more).  Does anybody know how to replace it?  Is it consumer
    replaceable?  What type of bulb does it take and where can I get parts
    if it is special (Nashua NH area)?
    
    The unit doesn't look easy to open up (probably for good reason).
    
    Thanks
    
    Ed

I've never seen a fuse IN a microwave yet.  It might be a transformer, or 
maybe the cord (does it get moved around by things in the cabinet over the 
unit?).  I would call a repair person if it's not an obvious problem.

The lights in most all microwaves are consumer changeable.  If there are no 
obvious access points inside the cavity, check the back, especially if the bulb
is near the back of the cavity.  My Amana had a couple of screws back there on
a plate, which hinged out the light fixture.  My over the counter GE gives 
access to the bulb by removing the plastic vent on the top front of the unit.

My GE uses bulbs made by GE... nice and available.  My Amana used bulbs made
by Amana... bummer.  

In both cases, I suggest:
	1) Reading the manual
	2) Stop by an appliance store that sells the unit, and 
		talk to someone who does service

    Microwave ovens DO have fuses, at least mine does.  Just trace the lot
    line from the plug on the way to the transformer and you'll find it.
    
    One thing to be careful about is a large capacitor that has the
    potential to zap you if you go polking about the innards.  You should
    discharge the capacitor as soon as you pull the cover.

    
    	I have a Sears microwave and had a blown fuse about 5 years ago.
    	It was a cartridge type fuse and was mounted on a fuse block where
        the power cord terminated inside the unit. I simply removed the 
        cover and the fuse, installed a new fuse and the unit has run
    	trouble free ever since.
    

Re: .1

For Sharp parts and service in Nashua, try P.E. Fletcher.

			Steve

    The base note asks if there is any danger opening up a uwave oven;
    there is danger and if your not fimilar with the circuits
    contained inside, you are better off leaving the problem to a
    service person.
    
    The inside of a uwave oven contains high voltage circuits powered
    by a constant current transformer needed to energize a magnetron. 
    Those circuits are far more dangerous than any TV circuit. I once
    worked on the electrical design of an oven and my recommendation
    is to stay out of the internal circuits unless you know what your
    doing.
    
    Joe

    I too also had a Sears microwave (1979 model), that would on an occasion,
    blow a fuse (Cartridge type - 15Amp? .45� +/-). I always keep a spare
    on hand for this occasion. But last year it would not cook and the fuse
    was good, yep - magnetron bad ;*( - at the cost of $110 for a new one
    from Sears, so I elected to buy a new Sharp (rated tops in Consumers) for 
    $199 on sale at Lechmere with more features (auto pop corn button -
    kids love it, me too!), auto sensor, etc....

    Good luck - maybe it is only the fuse....  

    Im a Service Tech for Washer, Dryer, Dishwashers, Trashcompactor,
    Microwaves, Air Cond, Ref, and my advice to you is to have a service
    tech who is trained to work on these kind of Appliances. take a look
    at yours, you can get killed from HIGH POWER VOLTS appox 2000volts in 
    a Microwave if you do the wrong thing. Im not telling you this to put
    fear in you. but to protect you, don't be a do it yourselfer when it
    get to Microwaves that a NO NO. to me it sound like you may have a
    fuse problem. because the light and fan stop working. call a small
    appliance shop for the best price. if you have lots of money call Sears
    or Lechmeres. Im in Boston area
                                        Jamez or BOOVX1::Darby  
                                   

    If you can't remove the plastic cover by the light then the microwave
    must be opened up to replace it, it takes a microwave APPLIANCE bulb
    sold at almost any store.
                                 Jamez or Boovx1::Darby
        

    Re:4393.2   All Microwaves have a fuse in them for Over load
    Protection. some may have breaker but most have a fuse.......
                                           Jamez
     

    
    
    	This has nothing to with the original question on this note, but
    	it's related to microwaves, I hope you don't mind me putting it
    	here.  This is what happened to me:
    
    	I have a smaller size microwave which has been working fine all
    	this time, I think it's a SHARP model.  One time, the microwave
    	was off, so I opened the door to put some food inside, as soon
    	as the door was open, the microwave started to work.  By that
    	I mean, you could hear the motor running.  I was surprised, so
    	I closed the door right away, the motor went off. I opened the
    	door again, and again the motor started running.  I unplugged
    	the microwave from the wall, and plugged it back, then opened
    	the door again, again the motor started running.
    
    	I didn't know what else to do, so I opened and closed quickly a
    	few times, until the problem went away.  Since that time, it has
    	been running fine.  Has anyone had this problem ?.
                                                          

RE: .1 to .10

Before this discussion is turned into another topic, let me thank those who
shared their thoughts on this with me.

My original fear in opening the microwave up is in case I break something or
if I do not seal things tight enough so there are some leaks.  The problem
with high voltage did not occur to me.  The microwave has been unplugged for
well over a month, so I would not expect there still to be such high charges.

I am still waiting for someone who has worked on a Whirlpool unit to give
me some more explicit directions if possible.

    No matter how long its has been unplugged if you don't discharge the
    cap before you work on it you can get ZAPPED. you can take the cover
    off with out breaking anything or causing a leak as long as you don't
    remove the door. and a microwave is a microwave no matter who makes it
    thay All work the same the only differance is the options ie. defrost,
    digital display, probe, timers, clock, ect...
                                                   Jamez 

    I have a Roper gas stove with a built in Micro.  It is about 10
    years old.  How do I change the light bulb?  Do I have to pull the
    stove out from the wall and remove the back panel or do I somehow
    access the light from the front?
    
    Thanks,
    
    Carl Lanteigne

    This has to do with a GE Spacesaver model.  It sits over the cooktop
    of a stove mounted underneath cabinets.
    
    The 2 bulbs that supply light, either as FULL light or as a NIGHT light
    under the microwave, went out at the same time.  After going to various
    hardware stores and not being able to find them, I called a local
    appliance store which had the bulbs ($4.50/bulb!! but thats another
    story).  Went home, screwed the bulbs in and the lights come on! 
    Tried the "NIGHT" light setting, hear a click (which is probably a
    relay) but the intensity stays the same!  Called the appliance store
    where I bought the bulbs figuring that for $4.50 the bulbs probably
    have a special filament for the "NIGHT" setting.  Turns out not to be
    the case.  Gentleman at the store says it's probably the "rheostat" and 
    no he won't take back the bulbs and refund the money...OK, I can live
    with that but...I really liked that "NIGHT" setting and this sounds
    like big $$$ and time , since I'll have to unbolt the unit from the 
    wall/cabinets and bring it in for repair.  Now a "rheostat" to me
    sounds like a resistor that's probably put in line with the bulb to dim
    it.  Anyone ever replace one of these?  Anyone ever take down a GE
    Spacesaver from its location??  I have no idea what one of these
    weighs.
    
    Yes, I understand the dangers of microwave leakage but it sounds to me 
    that I'd simply be taking off the units exterior skin(s) and working on
    the electrical portion NOT removing the door and/or messing with the
    magnatron (sp?).
    
    -TB

    I installed one of these by myself last year...It would have been
    easier with two people 'cause it's pretty heavy. I pulled the stove out
    so I could get directly under it to hang it on the bracket.
    
    I also had a problem (not with the light) and when I removed the front
    cover there was a nice set of schematics inside. I was able to fix the
    problem without even removing the microwave from the wall.
    
    good luck....             Paul
    

I get the bulbs for my GE spacesaver from the grocery store.  I forget the 
price, expensive, but not $4.50.  Probably around $1.50-$2?

Mine blow about every 3-4 months, so I always keep a supply on hand.  All the
frequently used bulbs in my house blow often, though.  That's probably something
to do with being at the end of the line from Fitchburg Gas & Electric.

    re: .23
    
    Paul,
    	When you say that you pulled the front cover, is that the front
    	of the unit including door or just the air-dispersion grille up
    	on top?  I can see that the grille will come off with 2 screws
    	but I don't see how the front cover would come apart.
    
    	Thanks for any info..
    
    	-Tony

re.    <<< Note 441.24 by RANGER::PESENTI "Only messages can be dragged" >>>

>Mine blow about every 3-4 months, so I always keep a supply on hand.  All the
>frequently used bulbs in my house blow often, though.

	   You might want to try getting 130V bulbs.  They're a little more
	tolerant of aggressive electricity... and they'll save you a few
	pennies on your electric bill.

Never heard of them?  Where can they be obtained, and how much more do they 
cost?

By the way, checked my cache of bulbs, and the 40 watt hi intensity lights that
I use (sylvania & GE) are $1.99 at Market basket.

    Re: .26
    
    I can see where the 130 volt bulbs would save you $$ on buying new
    bulbs, but, they don't save electricity.
    
    Marc H.

re	<<< Note 441.28 by JUPITR::HILDEBRANT "I'm the NRA" >>>
>	I can see where the 130 volt bulbs would save you $$ on buying new
>	bulbs, but, they don't save electricity.

	Marc,

	   Do you know Ohm's Law?  I had the math all figured out so you
	could see the numbers even if you never heard of it. Unfortunately,
	this node messed up and all my work went off to some computer
	burial ground somewhere.
	   What I remember:  A bulb burning 60 watts at 120 volts would 
	have a resistance of 240 ohms.  60 watts at 130 volts = ~283 ohms.
	The higher the resistance, when used with a lower voltage, means
	less current flow through the lamp. In laymans terms, less current 
	means you use less electricity.  It wouldn't be much savings but 
	could offset the added cost of the lamps.

	   E=I�R   E:Voltage  =  I:Current  �  R:Resistance
		     120 V    =      I	    �      240
		     120 V    =      I	    �      283
	
	   The actual (RMS) voltage to your house should be more on the 
	order of 115 volts.  If it's running high, that could account for
	the short life of your lamps.
	   Another alternative to 130V bulbs are a rough duty type.  I
	don't remember what they're called but you should be able to find
	them and the 130V style at most any electrical supply store.  You
	might even consider miniature flouresants. They use 1/4 the power
	to deliver the same amount of light as conventional bulbs.  They
	also last up to 10 times longer and will more than pay for them-
	selves in energy savings.

					Tim

I've picked up el cheapo made-in-China 130V bulbs for 19� or so.  It might
have been at Grossman's Bargain Outlet, but I haven't seen them as a regular
item anywhere.  BTW, I didn't really want 130V bulbs (I think they give
less light), but I didn't notice till I got home.

    Gee thanks Tim.....Golly, there is an Ohms law???? Wow....
    
    Getting by the crack, yes Tim, I know Ohms law. 
    
    My comment was related to the fact that a bulb's light output is not a 
    linear function with regard to power in/light out. A 120volt bulb
    operating at 120 is more efficient than a 130 volt bulb operating at
    120 volts. For the same light output, a 120volt bulb draws less than
    a 130 volt bulb. Now, bulb life is not linear either.....a 130 volt
    bulb operating on 120 volts will last much longer than a 120 volt
    bulb operating on 120 volts.
    
    Clear now????
    
    Marc H.

    
	re -1.

	    Sorry, but it's not clear.  A 130 volt 60 watt bulb connected
	to a 120 volt line would burn ~54 watts and would likewise be dimmer
	than a 120 volt lamp.  It seems to me you're saying that lumens and 
	power do not correlate because of different voltage ratings.  This
	may be true but I don't see how.
	    Wattage in this situation is related to heat.  If a filament
	is `burning' at a given power level, would it not produce a given
	amount of heat?  And isn't the amount of heat proportional to a
	certain number of lumens?  I'm talking about strictly incandesant
	bulbs.
	    Sure, you could talk about the coefficient of resistance with
	relation to temperature (of the filament) but I believe it gets
	nearly flat as the filament approaches operating temperature.

					Tim

    Re: .37
    
    Tim....lets try another way. The lumens are not proportional to power
    to the bulb...rather to the temperature of the filament. I believe
    that the visible light output is related to the fourth power of the
    temperature of the filament, for tungsten.
    
    Now, the infared output is different. Here, ohms law works since the
    power/heat is conserved...less power in, less heat.
    
    The key is that the visible light is NOT linear to the heat/power to
    the bulb. Consumer research/popular science talked about this subject
    about 5 years ago when the 130 volt bulbs were being made available.
    The recommendation then was use them where a *replacement* is difficult
    ,i.e. 40 feet up in the top of a barn. They last MUCH longer than
    regular bulbs...but...cost more in power to produce the same light
    output.
    
    Hows that?
    
    Marc H.

The hotter the filament the more efficient the bulb is at producing light
and not heat.  But the hotter the filament the shorter-lived the filament
is.  A 130V bulb (run at 120V) is less efficient at producing light but will
last longer.  A 130V bulb that's rated at 60W (at 130V) may consume 54 watts
on 120V but produce less light than a 50W 120V bulb.  (numbers made up here,
just an example)

Halogen bulbs are more efficient than normal bulbs mainly because they run
much hotter.  They use a trick to prevent burning out in a few minutes so
they're affordable :-)

-Mike

>	They last MUCH longer than
>    regular bulbs...but...cost more in power to produce the same light
>    output.

	Marc,

	   I concede... to a point.  I believe I understand what you're 
	saying.  It is something I had neither realized nor considered.
	But, I was going with the assumption that the bulbs were to be
	replaced with the 130 volt type of the same wattage.  With this
	in mind, my figures should still hold true except that the light
	output will be less than I'd imagined.
	   The reduction in light might be enough that the user would
	replace existing lamps with the next higher wattage.  I'll fall
	back on miniature fluorescents.  1/4 the power at 10 times the
	life for ~$10.00 a pop.  Rather a significant initial investment
	but a substantial savings in power AND labor over the long life
	of the bulb.

					Tim

    Re: .40
    
    O.K. Tim....all set.
    
    Marc H.

	You know that RotaWave (tm?) that Raytheon/Amana brags about in its
	microwave ovens?  Well, mine stopped rota-ing.  I noticed the oven
	was focussing its microwaves like a laser beam on either my coffee
	or pie, but not on both.  (OK, "maser" beam...)

	So when I removed the plastic false ceiling in the top of the oven,
	I found out what the RotaWave is.  It's a turbine with plastic vanes
	and four aluminum tabs.  The ventilation fan draws air through the
	cleverly baffled false ceiling so as to swirl around the turbine.

	My turbine rotates nicely when I poke it delicately with my delicate 
	pinky, but either it's dragging on the false ceiling, or its old
	bearing binds just enough to stop it.  It seems pretty free to me.

	To test for drag, I might stick a steel washer to one of the aluminum
	tabs, and try turning it with a magnet from the other side of the
	ceiling.

	Has anyone ever seen these little turbines refuse to turn?  Any thoughts
	on how to repair?  Have you ever spun the turbine by hand?  Did it sort 
	of rattle to a stop after one turn or so?

	Regards, Robert.

  I have a microwave oven that has mechanical controls; two similar controls
for the timer and power. As luck would have it, both knobs broke within two
days of each other. These are flimsy plastic things; I'm not surprised they
broke after 5 years. I called the local appliance repair shop (Bright Appl.
of Acton) and they said they don't have the knobs in stock and it will take
a week to get them. I can't wait this long. The only way I can use the oven
is to turn the control with Vise-Grips, and this is a major pain.
  If I had been on the ball, I would have asked the repair shop to rummage
around and see if they could find another knob that fits. This is a fairly
standard design: a hole 3/16" in diameter with a flat on one side. However,
the end of the shaft is flush with the front panel, so I can't use a knob
with a set screw like the ones that Radio Shack carries. (This is the first
thing I thought of.) There must be a dozen makes and models of appliances
that use knobs that are interchangeable with this one. But I doubt any master
reference manual exists.
  What I really need is to find a place that has a box of random assorted
knobs that I can rummage thru to see if I can find one or two that might
fit. Preferably within 10 miles of Littleton, MA. Any ideas?
  Please copy me on your reply.

    Many larger home supply stores have appliance knobs - often on a
    display with replacement stove elements, etc.
    
    				Steve

>    Many larger home supply stores have appliance knobs - often on a
>    display with replacement stove elements, etc.
    
  I assume you mean places like Home Depot and Home Quarters. Are there any
other "large home supply stores" around here? Sorry for my ignorance, but I'm
a renter and I rarely need to shop for home supplies.

    Well, those are the two larger chains in this area, but I meant my
    answer to be generic.
    
    				Steve

    check out spare knobs for TVs and radios at a repair shop or maybe on
    the parts racks at radio shack. Of course, the TVs and radios must be
    ones that use knobs, not buttons.

    Since you work in LKG and referenced an Acton appliance shop, you're
    withing reasonable striking distance of Somerville Lumber on Rt 27 in
    Acton. From LKG, take Rt 119 east into Acton, at the junction of 119/27
    take a left, and S.L. is a few miled down on your left. 
    
    If you don't like the generics, just use them until the appliance shop can
    order the exact replacements...
    
    good luck                            

>                    -< Somerville lumber is close to LKG  >-

  Do they have a box of replacement knobs that people can rummage thru to see
if there is one that might fit? That's what I'm really looking for.
  I tried Home Quarters and Home Depot over the weekend; they don't carry
replacement knobs for appliances.
  A TV shop might be worth trying. However, most electronics knobs require
that the shaft stick out 1/4" or more from the panel. On this microwave, the
shaft is flush with the panel, so that limits what replacement knobs I can use.
  I got the knobs from Bright Appliance today. $10 each. I would still like to
know if I can get cheap interchangeable knobs for future reference. They said
that Whirlpool and GE use non-standard parts and this makes it much more ex-
pensive to get replacements.

    Anyone care to explain to me why a microwave would turn on
    automatically when the door is closed but will not turn off?
    It also does not cook anything either. It worked fine last
    night. Today, it's dead. I either have to leave the door
    open or turn off the power to the microwave it order to shut
    it off. Any idea what going on here?
    
    thanks,
    
    John

    Stop using it and take it to a repair shop.  Microwave ovens are not
    a DIY repair job.
    
    					Steve

    Thought it might have been something simple. Funny, I currently have a
    microwave with this problem. I went to the Lechmere clearance outlet in
    Salem a purchased a replacement. It too has that same problem!! It's
    not a power thing either because I tried a few different outlets.
    Whatever the fix is for one, will solve the other. I thought it might
    be something as simple as a reset button.
    
    thanks,
    
    John

Are both the same model?  I've never heard of this symptom and it sounds
extremely dangerous if the magnetron does come on in this state.

				Steve

re: .46

>Are both the same model?  I've never heard of this symptom and it sounds
>extremely dangerous if the magnetron does come on in this state.

Steve:

Since he said it doesn't cook either, it doesn't sound like the magnetron
is coming on.  Nonetheless, I also would be leery of dealing with it if I
didn't know what I was doing.

-Hal

    
    I am doing a complete remodel of my kitchen and I
    am looking to get some info on the new "convection"
    microwave ovens.  I am going to be putting a built-in
    microwave over my stove with a vent to the outside.
    
    I want to know if anyone here has an info or experience
    with these new "microwaves".
    
    Thanks,
    Mike Smith

New?  I've had a convection-microwave for 8 years.  Some people love them,
others don't.  I find the convection feature works well for broiling, I don't
use it for much else.  I did roast a turkey using the "mix" feature (both
microwave and convection) and it worked well.

				Steve

I bought an Amana Convection/Microwave oven about 15+ years ago.  I had 
nothing but problems with it.  The inside frame around the door split and
was replaced twice in the 1st 2 years of it's life.  When the temperature
inside the oven got too warm, the oven's electrical system would pulse then 
blow a breaker.  Amana never could figure out why it was doing that.  They 
ignore my requests for repair or a new oven after thry tried to fix it for 
3+ years.

I now have a regular microwave oven and a convection/radiant oven.  I won't
mess with the convection/microwave any more.

Judy

We installed a convection oven and a built-in convection microwave oven just
before Thanksgiving.  Both are KitchenAid.  Installing the built-in
microwave involved a bit of a hassle because the outside vent ductwork from
the old range hood didn't quite line up, but I made it work.

Last Thanksgiving was the first time that I can ever recall my wife not
complaining about the cooking arrangements.  We only had 17 people for
dinner this year, and my wife used the oven in both normal and convection
modes, the microwave in both microwave and convection modes, in addition to
two other microwaves.  (I'm glad I finished that 200 amp service upgrade
last summer).

Her comment on the microwave/convection is that it doesn't heat large dishes
(like the ones that barely fit in the cavity) as well as the convection
range.  For physically smaller dishes that have some airspace around them,
it works fine.  The microwave/convection and the range were used to bake
five pies in the course of an hour, and *I* didn't detect any problems in
multiple samples ;-).

Make sure you have a dedicated 15 or 20 amp circuit for this beast - I had
to run a new one.