Re: Apple IIgs random hardware crashing - any ideas?

[ToasterKing <toasterking@SPLATbigfoot.com>]

In article <20031016051017.19539.00000360@mb-m07.aol.com>, Michael J.
Mahon <mjmahon@aol.com> wrote:

> ToasterKing wrote:
> 
> >Okay, as a follow-up to the totally bizarre behaviour of my ROM 3 IIgs
> >as of late, I've stumbled upon something interesting.  Last night I
> >completely removed the IIgs motherboard from its case, and reinstalled
> >the cards and reconnected the cables with it sitting unhoused on my
> >wooden shelf.  Ever since then, it has worked fine.  I used it for a
> >few hours last night with SCSI and full acceleration and never had a
> >problem.  Since then I've left it repeating the built-in hardware
> >self-test for 24.5 hours, and it hasn't failed once.  (Formerly it
> >would fail within 15 minutes of repeated tests.)  The funny thing is I
> >see no way any part of the board could possibly be shorting to the
> >ground shield in the case -- it has more than enough clearance
> >everywhere.  I've also tested to be sure that the add-on ports
> >installed in break-out panels in the rear of the case (connector for
> >SCSI card, jacks for sound card, hyperstudio sound-sampler add-on card)
> >and the power supply are not causing ground loops, both by checking
> >with an ohmmeter and by disconnecting/removing them.  The GS still has
> >crashing problems only when the board is seated in its case.  (The
> >board has been removed/reinstalled several times and still this remains
> >true.)  I've also tried poking/prodding/thumping the board while out of
> >the case and while performing intense operations to see if I could
> >invoke a crash, which would indicate I had a cracked trace, cold solder
> >joint, or other loose connection, but still it refuses to crash outside
> >of the case.  Also, the video corruption I mentioned while running NFC
> >Megademo disappears when the GS board is removed from the case.
> >
> >Now at least I know my board is okay, but this is driving me crazy! 
> >Does anyone have any bright ideas I neglected to consider??
> 
> Wow--nice problem.  ;-)
> 
> Seriously, intermittents are the worst problems to troubleshoot,
> for all the reasons you have found.  There are three basic approaches
> to fixing them, each with its advantages and disadvantages:
> 
> 1) Fix things that might be wrong and then test extensively
>    to see if the problem is fixed.
> 
> 2) Monitor critical signals to see what is failing when the
>    fault occurs, permitting the fault to be localized.
> 
> 3) Find some way of making the intermittent fault occur at will,
>    permitting the fault to be localized by ordinary methods.
> 
> You've done a lot of inspection and fixing (a la 1) without success.
> 
> You've found a variation of 3) in which the fault does _not_ occur.
> 
> (This is where some smart alec usually suggests running it
> without a case.  ;-)
> 
> The only effects that the case could reasonably (?) have are
> 1) raising the temperature locally (not very likely), or 2) putting
> mechanical stresses on the board that you have not been able
> to reproduce manually (a bit more likely).
> 
> I'd suggest suspending the board outside the case by several
> points (perhaps resting it on 6-12 erasers) and then--while
> running a diagnostic that usually exercises the fault--pressing
> locally with a pencil eraser to produce some board bending.
> 
> Work your way around the board, watching for a fault.
> 
> If you don't find any pressing on the top of the board, turn it
> over and repeat the test pressing on the bottom (this will
> flex different traces).
> 
> You probably don't want to hear that problems like this can
> often be caused by almost invisible cracks in traces, often
> near solder joints or vias.
> 
> Some folks might just bite the bullet and resolder everything
> in sight (a method 1 overkill), but "fixing what ain't broken" is
> a risk I would rather avoid.
> 
> I repeat, you have a worthy problem, and when you find and
> fix it, you can be proud of yourself!  (And let us know, so we
> can be proud of you, too.  ;-)
> 
> -michael
> 
> Check out amazing quality sound for 8-bit Apples on my
> Home page:  http://members.aol.com/MJMahon/

Hi Michael,

I can't really say much except thank you.  You've provided several
possibilities of problems and of their respective repairs.  As of now,
I still haven't been completely successful with method 3, but flexing
the board seems to cause at least some small influence on the crashes. 
As far as method 2, I have neither the schematics nor the oscilloscope
to test most of the relevant signals there, so I'll have a difficult
time monitoring during a crash.  And since I don't have infinite spare
time, I haven't been able to dedicate full resources to finding the
problem, but if I am able to fix it or at least find out what is
causing it, I will be sure to let you (and everyone else) know.  Thanks
very much for the reply, and I'll return the favour if I can.

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