Star Wars Math RAM (5F and 5H) and Mathbox Ready errors

DogP

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Star Wars Math RAM (5F and 5H) and Mathbox Ready errors

Hey,

My Star Wars Cockpit is having some problems... when I try to play a game, it starts, but there's never any enemies, and from the test mode, the first test gives me:
Math RAM at 5F
Math RAM at 5H

Then going further in the test, I get:
Bad Mathbox Ready Line

I've replaced 5F and 5H, but that didn't make any difference, so I think there's something wrong with the circuitry further up. I assume that the Mathbox Ready Line is bad because of the same problem (or the RAM problem is caused by the Ready Line problem).

So far, I've done some searching and came across suggestions to replace 4F and 4H, so I did, but it made no difference. I also swapped with a known good AVG chip, since I've had several of those cause funny problems, but that didn't help. I used to have an upright, and back then I verified that the problem is on the main board (middle board in the stack). The voltages are good and the monitor is good.

I'm running Mark Spaeth's SW/ESB multi kit. Any ideas on what I should check next?

Thanks,
DogP
 
Those are the PROMs though, right? I've got new ones that came with the multi kit, though I could try swapping back to the originals (I think I have a set of good originals). I believe no enemies is an effect of the Mathbox Ready line being stuck low.

DogP
 
The PROMs didn't make a difference... any other ideas?

Thanks,
DogP
 
Okay... well, I got kinda annoyed troubleshooting this board, so I popped in a couple dead main PCBs that I had laying around... one was completely dead (watchdogging), so I set that aside... the other had a bunch of errors, but did actually do the self test. When I looked at those errors, it said RAM 5F was bad, as well as all RAMs/ROMs on the AVG board. Knowing that the AVG board is fine, I looked for the communications path between the boards and found 0D/E, which is a 74LS245. I replaced that and all the AVG tests came back fine... but there was still a RAM error. In the game, this error showed up as jumpy enemies and sometimes long lines drawn.

So... I swapped RAM, but it still complained about 5F, so I knew it was the 5F circuit, not the RAM. So, I started probing, and noticed that the test passed whenever I held the logic probe on the /ENB pin. The probe said the logic levels were good, and since I've had quite a few other bad 74LS245s on these boards, I decided to replace 4F (74LS245). This ended up fixed the problem, so now I can play my game again :) .

If anyone has any ideas on the other board, I'd still like to fix it, since that's the original main PCB, but for now I'm just happy that it's working again.

DogP
 
If you replaced those other ones and it made no difference, it could be the socket(s).
edit: Meter them out to make sure you don't have a bad trace or socket.
 
Similar, except mine was in the Y direction. Like in the trench, the turrets on the sides would sometimes have vertical lines that were the whole height of the screen.

DogP
 
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