Conference hydra::amiga_v1

    One more note... 
    
    After being powered off over nite I tried it this morning and
    everything worked!  No scrambled Icons.  After about 5 minutes I
    checked the Icons again and they were scrambled.  HEAT related, no
    suprise.
    
    I guess it's time to crack open a can of freon and see if I can locate
    the failing chip.  One other thing I thought of this morning is perhaps
    it is the A2090.  I should try using floppys only with the SupraRAM
    installed and see if I still have the problem with Deluxe Paint.
    
    ...Ed

    Ed,
    
    So far you're doing everything right.  This current hardware type :-)
    recommends looking at the motherboard first.  From your "scrambled
    icons" description the most likely problems are in the Commodore custom
    chips, the chip RAM devices, or the memory controller chips.
    
    Wes

    
    Ed,
    
    	Personal experience and talking with a couple of authorized repair
    people leads me to look at the power supply first. Older Amiga 2000 and
    2500 systems have a problem with the power supply. When they get older
    the power supply shows heat related problems. The problem can cause
    all kinds of strange things to happen. The more load you have on the
    supply the soon the problems show. The only fix is to replace the
    supply.
    
    		Steve P.
    

    
    I don't have a 2000, but I am also an ex-hardware type...
    
    I agree with Steve Peters' observations, and I tend to think that
    perhaps the large filter capacitors (assuming they have some; be
    darned surprised otherwise) might be pooping out. Since you have
    a 'scope, watch the ripple closely. It could be quite a trick to
    troubleshoot it if you have to open it all up to probe various
    places in the hopes that it's a heat-related problem! (Use a
    blanket, perhaps?).
    
    There may be some resistors in the regulation feedback circuit(s) that
    could be changing value with temperature after being in service for
    several years. Also, inspect the power wiring harnesses and their
    connectors carefully; a dirty/corroded contact may be adding some
    resistance which will increase with heat and further aggravate the
    problem. A discolored plastic connector housing is a tell-tale sign.
    (Any one remember that one from the PDP-11/40?).
    
    Is there an internal fan? If so, is it working properly? (If it's
    become dirty and/or slowed down, it can't push air properly). Are
    the components (CPU chip, graphics chip[s], etc.) dirty or dusty?
    Dirt/dust will tend to act as insulation and reduce the amount of
    heat dissipated to the air, causing the die to overheat.
    
    Let us know how you fared.
    
    Bayard
    
    

    I remember reading (on USENET) some time back someone who had icon
    problems such as you describe. It turned out to be a bad blitter chip.
    Their problem was permanent (ie not heat related) until they replaced
    the chip.
    
    John

Thanks for the ideas.  I'll definately check the power supply.  The heat 
related part of the equation it fails always after being on a few minutes
after a long cooling off period.  It does fail with all the covers removed so
if it's a chip I can hopefully isolate it by cooling them down one at a time.


re: .5

What's the blitter chip?  Is that what it's called in the circuit diags in the
back of the manual?  What is its function in life?


Cheers,


...Ed

>    I guess it's time to crack open a can of freon and see if I can locate
>    the failing chip.

Can't you find a way to solve your problem without using up more of our
ozone?  Maybe if they made the stuff $1000/can ...

	Paul

    re -.7
    
    Yea, I guess they don't sell freon anymore.  Since I don't have any now
    I'll be buying what ever the latest coolant spray is made from.  Last
    time I had to cool some components on DEC equipment freon was it.  
    
    They do sell something else now I hope...
    
    I'm not one to knowingly contribute to global warming.  Hell, I don't
    usually drive a car to work, I bicycle in, and thus likely contribute
    less to the global warming that most. :')
    
    Cheers,
    
    ...Ed
    
    

    
    
     The replacement freeze spray contains no CFCs.  It does contain
    chlorodifluoromethane which, the can says, is EPA exempt/non-regulated. 
    It freezes to -96F so be carefull!  It can crack ceramic ICs. (Not to
    mention cause frostbite)
    
      The stuff is made by Chemtronics.

    
    Judging by your re-stated failure mechanism, I'm now wondering if
    you might have a cracked etch or a cold joint that is separating
    at temperature.
    
    So, don't just chill the IC's, but take a suspicious look at the
    rest of the board.
    
    

    Well 'component cooler' saves the day.  After checking pwr supplys I
    cracked the coolant can and started selectively spraying ICs.  I
    started with the A2090 with no luck.  I then attacked the motherboard. 
    My test was to keep opening the drawer with the scrambled icons.  When
    I froze the 68K, bingo, the icons were no longer scrambled.  I repeated
    this 4 times to be sure, letting the 68K warm up enough each time to
    observe the failure.  After removing the motherboard I removed the 68K
    and checked around at all solder joints/etches.  I found a sloppy
    looking joint on a 470 ohm pullup on the 'DTACK' line and resoldered
    it.  Re-installing the 68K gave me a bit of a scare.  For anyone who
    has done this on an A2000 probably notice, its in backwards to all the
    other chips.  That is the other chips have pin 1 facing the back of the
    machine while the 68K's pin 1 faces the front.  My entering this note
    proves I put it back the right way ;')
    
    Anyway not sure if re-seating the chip or re-soldering the pullup on
    DTACK fixed the problem.  If it returns I'll replace the 68K I think.
    
    Cheers, and thanks for all the ideas.
    
    ...Ed

    Well looks like I'm in the market for a new 68K.  My wife was using
    Amy all day today and tonight I find the Icons are scrambled again.  I
    was sure it would be the pullup resistor on 'DTACK' but looks like it's 
    the 68000 IC.
    
    Anyone in the MA/NH area running a 68010 that would like to unload
    their 68000?  Send me mail if ya have one lying around.  Otherwise
    I guess I order a new 68k.
    
    
    Cheers,
    
    ...Ed
    

    Re .12:
    
>   Anyone in the MA/NH area running a 68010 that would like to unload
>   their 68000?  Send me mail if ya have one lying around.  Otherwise
>   I guess I order a new 68k.
    
    The ATonce board also displaces the stock M68000, so I have one to
    spare.  What're you offering?

Well about two days after replacing my 68K I had the same problem return.  It was
still failing when the 68K warmed up and ok when cooled down.  Last week I
had some more time to work on it so I pulled the motherboard again and 
re-soldered every connection within 2" or 3" of the 68K.  Bingo, no more
problems for almost a week now.

A happy camper again,

...Ed (now on to 2.0 upgrade)