Conference hydra::amiga_v1

>The only motherboard difference between B2000 4.4 and the latest is an extra 
>pullup (1k will do) on the expansion bus BAS* line.  This can be added between
>pins 11 and 20 of U605 on the motherboard.  The A2620 has had no running 
>hardware changes since its introduction; I don't know about the others.

Okay, I admit it.   I'm a software weenie.  Now would someone please humor me
and tell me exactly what this means?  Am I correct in assuming that what's
being said here is that if I add a wire between pins 11 and 20 on socket/chip 
U605, then my rev 4.4 board will be equivalent to a rev 6.0?

(I just need a little help now and them, you know.)  %-)


					John 

> Okay, I admit it.   I'm a software weenie.  Now would someone please humor me
> and tell me exactly what this means?  Am I correct in assuming that what's
> being said here is that if I add a wire between pins 11 and 20 on socket/chip 
> U605, then my rev 4.4 board will be equivalent to a rev 6.0?

AAAAHHHH! Not a WIRE, a PULL UP (Resistor) of 1k ohms (that's brown black red)
and say 1/4 watt 10% (thats brown black red silver). Cost about $0.19 at
Radio Shack.

That and some solder should do it.

John

> The only motherboard difference between B2000 4.4 and the latest is an extra 
> pullup (1k will do) on the expansion bus BAS* line.  This can be added between
> pins 11 and 20 of U605 on the motherboard.  The A2620 has had no running 
> hardware changes since its introduction; I don't know about the others.

These guys are a riot. If you look on page F10 in the A2000 schematics, 
the _BAS line is just a couple down from the _BUDS and _BEER lines!

John

    just what is this pull-up resistor supposed to do for your cpu???
    i mean what problem is it going to correct??? just curious...
    
    
                    dave peterson
                    node   husker::
    
    

It fixes a problem with DMA devices in the expansion slots...

 mark

Is it worth doing the fix? Will it affect the A2090a?

John

    The fix is only for those systems with an A2620 board. Also, there
    has been a ROM change on the A2620 to correct a bug in the first
    release. The Rev -2 roms can be ordered through an authorized service
    center. They are socketed.

   <<< Note 2815.7 by DICKNS::MACDONALD "WA1OMM 7.093/145.05/223.58 AX.25" >>>

>    The fix is only for those systems with an A2620 board. Also, there

NO, i had trouble with my 2090A (bad headers, random r/w errors). This fix
cured all my ills.

 mark

I called CBM tech support.  Basically, they don't support the Amiga!

They are moving that to the service centers. "It's too technical and involved" 
the lady told me.

So I called Memory Location. Their tech is on vacation till next week,
call back Monday.

Called The Software Shop. Moe was busy but the guy who answered didn't
think the -2 ROMS were released yet. Call back...

So I then proceded to try to copy a file for a friend. My lovely Rodime
disk crashed *again* (3rd time in 1 month!) Read/write errors, can't validate,
not a dos disk etc... Won't boot. Damn.

Oh well, looks like the pull-up fix may be the thing. And the new ROMs
when available.

CBM? Do you really want the Amiga to be the success it should be?

> A2000 Motherboard Rev 4.4 -> latest  (6.0)?

The guy at The Memory Location said their latest motherboards are rev 6.1

John

    Dave Haynie and other CBMers have said on Usenet, and as a hardware
    guy I trust them, that only a couple of design bugs were fixed in
    all the motherboard revs.  The rest were made for a cleaner layout,
    to make the board more easily manufacturable (i.e. for autoinsertion
    equipment), and for other reasons not related to the electronic
    design.
    
    Before you get too excited about which motherboard you have, just
    remember that only a couple of real hardware fixes have ever come
    out for the 2000.  Perhaps someone can dig out the short list (as
    a non-owner of the 2000, I haven't paid attention).
    
    Wes

Following is a mail message I sent to Dave Haynie at Commodore and his reply.

Only Amiga...




Hi Dave!



I hate to bother you but your about the only person I know who can solve this!


I have an A2500 with Rev 4.4.  I saw your note on USENET about the pullup
fix on the BAS* line (Saw this line in the schematics next to the BUDS and
BEER lines :-).  

You say this fixes problems with DMA devices on the expansion bus. I've since
heard that it is only for A2620 based machines and also that it fixes a problem
with the A2090a. I even hear of Rev -2 ROMs for the 2620 which fix a bug.

I'm concerned about the possibility of the A2090a fix. I have had my
machine for about 2 months now, and have had 3 hard disk crashes (read/write
errors, unable to validate, not a dos disk etc!). So I have some questions
which I'd be eternally gratefull if you could answer:

	1. Does this fix affect the A2620?
	2. Does this fix affect the A2090a
	3. Are there new ROMs (Rev -2?) for the A2620
	4. If yes on #3, what do they fix?
	5. Will doing this pull-up fix bring my 4.4 to 6.1 (assuming
		I have a new fat agnus and ignoring etch relayouts)


Dave, again thanks for any help here. I really love this machine but am
now afraid to use the HD...

John
(Digital Equipment Corp. Marlboro, Ma.)





From:	DECWRL::"[email protected]" "Dave Haynie  10-Aug-89 1149 EDT" 10-AUG-1989 12:55:51.56
To:	[email protected], wjg::guineau
CC:	
Subj:	Re:  A2620, A2090a and Rev 4.4 fixes

>Hi Dave!
 
>I hate to bother you but your about the only person I know who can solve this!
 
>I have an A2500 with Rev 4.4.  I saw your note on USENET about the pullup
>fix on the BAS* line (Saw this line in the schematics next to the BUDS and
>BEER lines :-).  
 
>You say this fixes problems with DMA devices on the expansion bus. I've since
>heard that it is only for A2620 based machines and also that it fixes a problem
>with the A2090a. 
 
The extra pullup can always be added; it's a 1K added between pins 20 and 11 of
U605.  Brings the system fully up to date.
 
The reason for the change is this.  When the bus is changing masters, there's 
a period during arbitration at which point no one is driving the bus.  I have
a set of pullups on the bus which pull it to a quiescent state during this
time, so no devices try to respond to a floating bus.  Actually, the only line
that really NEEDS to be pulled up is BAS*, since address strobe defines 
whether or not a cycle is taking place.  There are pullups on the bus on all
machines, but we found a problem with one brand of 74ALS245 chip, in that the 
supplied pullup (10K) didn't get BAS* high very quickly.  This caused problems
only, far as we know, with the A2620, for several reasons.  First of all, the
A2620 is on the far side of this 74ALS245.  The 245 is a schmitt gate, so it
takes the gradually rising BAS* from the expansion bus and turns it into a 
nice, square, pluse on AS*, which gets fed to the A2620 and the Agnus chip.
Agnus doesn't care, really, cause this happens too fast and at the wrong point
in the cycle.  But the A2620 is really fast, and it also latches AS* to safely
syncronize it's 14MHz stuff to the 7MHz DMA stuff, so it in effect extends 
this AS* glitch, and ends up running a bogus cycle.  
 
Other CPU cards may act similarly, though we haven't seen the problem effect
anything else.  It could possibly, and the pullup doesn't hurt in any case
(and it's been made a permanent change for the Rev 6 board as well as a 
running change in the Rev 4 -> Rev 4.4 + this resistor = Rev 4.5).
 
>I even hear of Rev -2 ROMs for the 2620 which fix a bug.
 
There was a bug in the A2620's autoconfigure logic (used mainly for UNIX and
the A2620 monitor) that caused it to get confused by 128K PICs.  The only
128K PIC we've run into is the GVP hard disk controller.  The -2 ROMs, which
they tell me are a standard Service item now, fix this bug and apparently
several other very minor ones.
 
>I'm concerned about the possibility of the A2090a fix. I have had my
>machine for about 2 months now, and have had 3 hard disk crashes (read/write
>errors, unable to validate, not a dos disk etc!). So I have some questions
>which I'd be eternally gratefull if you could answer:
 
>	5. Will doing this pull-up fix bring my 4.4 to 6.1 (assuming
>		I have a new fat agnus and ignoring etch relayouts)
 
Yes.
 
>Dave, again thanks for any help here. I really love this machine but am
>now afraid to use the HD...
 
I'd definitely recommend the pullup fix for any A2620 system.  We have no 
known case of a problem without the A2620 installed, but since the problem
that's fixed is really a bus problem, not an A2620 problem, it's a good idea
in general.  You never know when something else that's sensitive to this
problem will show up.
 
The major symptom of this problem with the A2620 is a hard disk crash.  However,
it generally gets so bad that the disk will crash in a minute or two of use.
That was pretty handy, actually, since something that fails so regularly is real
easy to track down in the lab.  You may have a system that's just on the hairy
edge of having a problem.  The parts that caused this problem are Signetics
74ALS245; we've always found the problem with Signetics, never with another 
part (though I suppose in theory it could happen), and the pullup is a 100% 
fix.
 
>John
 
>(Digital Equipment Corp. Marlboro, Ma.)
 
Hope this helps you out.
 
					-Dave Haynie
 
 
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     <<< Note 2815.12 by WJG::GUINEAU "Opening the doors of Perception" >>>
                           -< The definitive answer >-


>I'd definitely recommend the pullup fix for any A2620 system.  We have no 
>known case of a problem without the A2620 installed, but since the problem
>that's fixed is really a bus problem, not an A2620 problem, it's a good idea
>in general.  You never know when something else that's sensitive to this
>problem will show up.

I guess i'm not known, but without any doubt this resistor fix cured my
2090A problems. I have a note somewhere about my problem & solution. It
only takes a few minutes to solder the resistor onto U605 (with the correct
tools and some care). Give it a try and i'll bet your disk will work fine.
The problem is more severe if U605 is a Signetics chip (which mine was).

 mark
 

Did it last night. I did have the signetics chip.

One curious thing was that there was already a resistor there (on the chip)!
Except it was a 33K and there were no obvious markings that my motherboard
had been upgraded. It stil said 4.4 but this fix w/o new agnus should have
been 4.5 (I guess).

Since the original pullups are 10K, 33K won't make much difference.
I removed the 33K and placed in a 1K. We'll see...

John

    Here is a silly question.  I just bought an A2000 which the seller says
    is the "rev of motherboard just prior to Super Agnus release".  How can
    I tell (once I get my machine (thursday)) what rev the motherboard is?
    (4.4, 6.0, 6.1, 6.1B?)...is it as simple as reading "6.0" or is there
    a key version number that needs to be translated to simply "6.0"?
    
    Thanks,
    George
    
    Ps: Anything else a new 2000 owner should look for?  I'm upgrading from
    an A500...the 2000 has an A2090A HD controller connecting a CDC 150Mb
    Hard Drive.  Everything else is pretty stock (has an extra floppy
    too!).
    

re motherboard revision:

Take the cover off (2 screws on each side and one in the top middle of the back)
The revision is on the pcb in the front left corner.

john