Tempest Main Board Problem - Watchdogging

64B1T

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This is one of those things I would normally use my CAT Box on... But that thing decided it no longer wanted to cooperate.

I've been looking at a couple Tempest PCBs I have lying around. One of them I've got ALMOST working... But it resets when in game mode.


It's fine in test mode and audit mode. If I can get it to go to attract, it'll go through the whole attract sequence, but doesn't like the actual gameplay section.
I noticed that in the MCMLXXX Atari copyright message, at times it's prepended with a "B" between the copyright symbol and the M. so I feel like there may be some kind of ROM error going on?

It's not a mathbox problem. This issue is the same when I swap a mathbox from a known good boardset.
 
Figure out why your CATbox isn't working. :) That's the best tool for these.

One thing that is semi-common on Tempests is bad RAM that don't get caught in self-test. Piggyback each RAM and see if that B error (or the resetting issue) goes away. You can also try the ice cube trick, if you think the behavior is affected by temperature at all.

Other possibilities (less likely, but not impossible) :

You might also have a problem deep in the VG. Something with the vector timer or shifters, where it's choking on a vector of a specific length, which isn't drawn in test or attract mode, but is during gameplay.

Also, you may want to replace the TL082 in the power-on reset circuit, which can cause random resets. However if you're seeing a graphics glitch, I'd say that's less likely.
 
Figure out why your CATbox isn't working. :) That's the best tool for these.
Sigh, yeah, it's one of my favorite tools. I wonder what happened to it. I tried a different pod on a defender boardset I had on the bench and it didn't work either, so I'm pretty confident it's the CATBox itself. Fuuuuuuck.

One thing that is semi-common on Tempests is bad RAM that don't get caught in self-test. Piggyback each RAM and see if that B error (or the resetting issue) goes away. You can also try the ice cube trick, if you think the behavior is affected by temperature at all.
If only I had the cat box to look at the damn RAM!
I wonder what could be wrong with the thing.

I'll look at the RAM further when I get a chance. Nothing is socketed unfortunately and I don't want to pull RAM willy nilly. I do not think it's a VG thing, because it did manage to hold through a level at one point, and drew it fine, so it didn't seem like it was choking. Not sure.
 
Got the cat box going.

Think it was something intermittent with the LS139 at C1. Socketing it fixed the issue.
 
What was the Catbox telling you?

Was the 139 a Signetics chip?
Yup. Signetics.

The ROM read okay, but I found another post with this same problem, and this was the solution. Seemed to work here too.
 
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