From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: b2000 crashing part 3
Date: 16 Apr 92 20:32:59 GMT
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Distribution: comp
Organization: Commodore, West Chester, PA

In article <1992Apr11.1108.15261@dosgate> "kenneth tam" <kenneth.tam@canrem.com> writes:
>More information on this persistent problem I've been having..

>Scenario 1 - Expansion RAM and HD installed, booting off HD or WB disk.
>    It DIES.  Gurus like above, often at random times during the startup
>sequence, sometimes it goes through the startup-seq and dies when I run
>a program.  ... Definitely unstable.

Random crashes like you describe are generally the problem of some memory
failure.  Could be that either hard disk, CPU, or both can't always read or
write that memory correctly.

>Scenario 2 - NO expansion RAM, NO HD, booting C= 1.3 WB disk
>    It WORKS..  I can't seem to crash it.  

That's a good sign.

>    There's not much I can run w/o a HD and more than 1 MB RAM, but I opened 
>    a lot of windows, moved them around, ran a few clocks, ...

When doing this kind of test, always use the same programs, same startup-
sequence, etc.  You want to eliminate any software question when you're looking
for a problem with hardware.  If the software setup isn't exactly the same, you
may be mixing problems.

>Scenario 3 - NO expansion RAM, but HD installed.  Trying to boot from HD
>    The HD seems to automount on startup, but it won't boot.  Goes to
>floppy instead.  Once the floppy boots, I try to access DH0: but it's
>not accessible.  

It sounds like your Hard Disk's RDB specifically requires Fast RAM.  Run RDPrep
and check for this; you generally want the disk's memory type to be "0".

>What jumpers do I set on the motherboard to force the 1 MB Agnus to only give 
>me 512 K chip?

Jumper J500 (two point jumper), switch the position of J101 (three point 
jumper).

>Scenario 4 - Expansion RAM, NO HD.
>    Attempted the same things on this setup as in scenario 2.  It
>doesn't GURU, but it does freeze when I try moving windows around a lot.

This sounds like it's probably a memory failure, most likely in some critical
OS function, maybe you're crashing Intuition or something.

>I need help badly..  This doesn't make any sense to me.  The only thing
>I can think of is that somehow most of the motherboard works, except for
>the chips/circuitry that deals with the expansion bus.  What chip
>controls timing and access to the bus?  Can it be replaced easily?  

The Buster chip and a handful of 74LS245 and 74ALS245 chips comprise the 
A2000's expansion bus.  It's unlikely any of these are failing, though, chips
really don't fail of their own accord, and nothing other than the 8520s in 
Amiga systems is all that likely to get zapped from some external source.  Your
best bet, assuming you can verify that the memory board works in other systems
(a memory test is insufficient -- most memory tests are very simple minded and
don't detect bad parts, while running your code out the same board will, in 
interesting ways), would be to have a service center check out your expansion
bus for proper operation.  From what you describe, it sounds to me like a 
flakey memory board.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      BIX: hazy
      "What would they do if I just sailed away?" -Jimmy Buffett