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8032 Rom's in spare slot? bad screen display

MikeS said:
Geez, where else does a pinball machine belong if not in the living room???

I added a few questions; also, does it beep when it starts up (in either state)?
Click to expand...

Yes it does have the normal 4tone boot sound on power up.
 
polishedball said:
Yes it does have the normal 4tone boot sound on power up.
Click to expand...
It's really frustrating trying to remotely troubleshoot if you don't answer our questions...

Again:

- If you allow at least 10 seconds between power off and power on, does it still come up randomly in either of those two (and only those two) states?

- Once it's up, if you do nothing do both displays remain the same or do any locations change at all?

- If you type something or just hold down a typing key, do either of the displays change at all?
(I take it that even after holding the space key (for example) for ten seconds or so there is never a beep?)

and

- Which ICs did you replace?
 
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MikeS said:
It's really frustrating trying to remotely troubleshoot if you don't answer our questions...

Again:

- If you allow at least 10 seconds between power off and power on, does it still come up randomly in either of those two (and only those two) states?

- Once it's up, if you do nothing do both displays remain the same or do any locations change at all?

- If you type something or just hold down a typing key, do either of the displays change at all?
(I take it that even after holding the space key (for example) for ten seconds or so there is never a beep?)

and

- Which ICs did you replace?
Click to expand...

With 10sec between power ups it 9/10 comes up onto the first screen. These screens never change and there is no active data in them, they remain the same. There is never a beep and nothing changes if typing or holding down a key till what would usually reach the end.

I replaced all the DRAMS, SRAMS, the 74LS244's in ram section and the 373's in the RAM section. This made no change in the screen. I also swapped the 6502 no difference, and the character rom no difference.

Thanks
 
polishedball said:
With 10sec between power ups it 9/10 comes up onto the first screen. These screens never change and there is no active data in them, they remain the same. There is never a beep and nothing changes if typing or holding down a key till what would usually reach the end.

I replaced all the DRAMS, SRAMS, the 74LS244's in ram section and the 373's in the RAM section. This made no change in the screen. I also swapped the 6502 no difference, and the character rom no difference.

Thanks
Click to expand...
Looks like it's more than just a video problem then; if you still get the Commodore BASIC message that the first screen shows but the keyboard isn't recognized then I'd suspect one of the ROMS. Looks like it passes the RAM test but goes off into never-never land some time afterwards.

Sounds like you've got a programmer; if you've double-checked all the sockets and pins maybe it'd be worth while to read them and make sure they match the correct numbered images on Zimmers. You show both systems; I take it that this is the one with the EPROMS? 2532s except for a 2716 in UD7 (E0-8 )?
 
MikeS said:
Sounds like you've got a programmer; if you've double-checked all the sockets and pins maybe it'd be worth while to read them and make sure they match the correct numbered images on Zimmers. You show both systems; I take it that this is the one with the EPROMS? 2532s except for a 2716 in UD7 (E0-8 )?
Click to expand...

I'll read them back and compare checksums again. They were right when prg originally, but worth a check again. I used the images from zimmers making these. Thanks for the help, hopefully this weekend i'll have some time to really dig in and actually troubleshoot the board.
 
OK made some progress swapping out UC8, 9 and 10 as suggested, I also replaced the remaining caps that hadn;t been on the board. It now boots everytime and comes up to a cursor blinking and some can almost read text. When holding down space it moves the cursor and it beeps when hitting the end of the line. This is an updated picture. If anyone could give any more ideas on what to look at next. Thanks so much for the help so far. The garbage appears on the screen prior to the basic prompt comming up if that can help at all. Id did swap in some new SRAM again and it made no difference. The ram I am using is a replacement sub though part number AM9114CDC can anyone confirm that this can be used?

pg.jpg
 
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I did swap the character rom and the edit rom with known goods this didn't make any improvement. Doing a checksum check on the remaining roms.
 
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OK; looks like we're sort of back where we were; I'd suspect UC6 and/or UC7.

Edit: I see that you did replace the video RAM; did you replace all 4 and nothing changed? 9114 should be an OK replacement.

If you did indeed replace all 4 and there was no change then I'd suspect UB6, UB7, UB8 and UC3 in that order.

What does it look like with UC6 and UC7 removed?
 
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MikeS said:
OK; looks like we're sort of back where we were; I'd suspect UC6 and/or UC7.
Click to expand...

Swapped them with what I believe to be known good still have the same issue. If it is an sRAM issue would something change if I swapped UC4&5 with UC6&7. I'll also double check the socket work on them and ohm them out tomorrow. Gotta be to work in 5 hours. Any other ideas? Thanks again for your help and my apologies for the newbie mistake of not answering directly earlier your questions.
 
MikeS said:
OK; looks like we're sort of back where we were; I'd suspect UC6 and/or UC7.

Edit: I see that you did replace the video RAM; did you replace all 4 and nothing changed? 9114 should be an OK replacement.

If you did indeed replace all 4 and there was no change then I'd suspect UB6, UB7, UB8 and UC3 in that order.

What does it look like with UC6 and UC7 removed?
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UB6, UB7, UB8 are all socketed. I'll check them in my IC tester shortly. UC3 is not and as fate would have it I do not have a 74LS138 in my stock.
The screen looks like this with them removed.
eo.jpg
 
MikeS said:
I'd suspect UB6, UB7, UB8 and UC3 in that order.
Click to expand...

Ding Ding we have a winner, UB6 when tested in my checker came back as a 74LS185 not a 74LS244. Swapping this fixed it up. It now displays properly! Thanks so much for your guiding me through this.

John
 
polishedball said:
Ding Ding we have a winner, UB6 when tested in my checker came back as a 74LS185 not a 74LS244. Swapping this fixed it up. It now displays properly! Thanks so much for your guiding me through this.

John
Click to expand...
Excellent! Glad to see another PET resurrected.

Apologies if I sounded snarky about getting questions answered; I think we were just both editing our posts at the same time and missed the changes.

What part of the world are you in BTW?
 
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