Still Looking for Gravitar Help

Sorry for the repeat request, but I could really use some tips on
troubleshooting this Gravitar board. I actually dreamed I fixed it last
night... guess I've been really obsessed with repairing it.

Just to refresh, the #WDCLR timer pulses four times in rapid succession,
then stays high which causes a reset. Pulling #WDDIS low doesn't help in
troubleshooting, the address lines and data bus continue to run in what I'd
consider a "confused" state... there appears to be skinny pulses on the
address lines and major bus contention on the data bus. I swapped all the
socketed parts into a BW board and it comes up fine. All the clocks look
good.

I thought I found an issue with the #IRQ line last night. It is low and the
LS161 counter isn't counting even though #INTACK is high. Forcing the ENT
(pin 10, also the #IRQ line) line high causes the LS161 to begin counting.
At any rate, I concluded this anomaly is due to a startup issue (#INTACK)
since the #IRQ line loops back to ENT on the LS161.

When you guys end up going in loops on these things, do you just start
shotgunning? I think I'm at that point and was going to start with the
address decoders at R2, P3 and R1. The LS138 shouldn't be an issue, but
what should I do about the 136010-x11,x12? What exactly are they and are
they available somewhere?

Thanks,

Tim Tewalt

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Received on Wed Oct 1 16:26:27 2003