PEB 32K Memory Troubleshooting - Bad RAM

[mbliss11]

I was lucky enough to get a PEB locally. It only came with the interface card. I sourced a 32k card online listed as untested. You know what that means

I have finalgrom and a tipi32k sidecar. I found a memory tester cartridge file online and ran that against the card. Upper block is testing bad. There was another memory tester program I found on Atari age that used a minmemory cart. Problem is the tipi is not happy with the memory cart and I can’t use it to upload the file to the cart.

Any suggestions on how to test further. I’m hesitant to probe in the peb with the scope because it’s awkward but that may be the only option. Unless I just remove all of the upper ram chips and socket and replace. It’s all MOS branded ram should I just replace them based on that fact alone

 

[RetroAND]

I was lucky enough to get a PEB locally. It only came with the interface card. I sourced a 32k card online listed as untested. You know what that means

I have finalgrom and a tipi32k sidecar. I found a memory tester cartridge file online and ran that against the card. Upper block is testing bad. There was another memory tester program I found on Atari age that used a minmemory cart. Problem is the tipi is not happy with the memory cart and I can’t use it to upload the file to the cart.

Any suggestions on how to test further. I’m hesitant to probe in the peb with the scope because it’s awkward but that may be the only option. Unless I just remove all of the upper ram chips and socket and replace. It’s all MOS branded ram should I just replace them based on that fact alone

Try piggybacking all memories of the higher bank at the same time and repeat the test. If the problem is solved, then skip to next sentence, else test the logic components. If the error is located at the memory bank per se, remove a memory and pass the test. If the test is a success then repeat for the next memory, else put the piggyback memory again, repeat the test until it passes (to eliminate the possibility of poor contacts) and repeat for the next memory. When all memories have been tested you should have piggyback only on the broken memories. Proceed to extract and replace them.

With that method I repaired a TI-99/4A in a matter of minutes. I hope it helps you too.

 

[mbliss11]

Thanks for the reply! I had piggybacked only 4 chips at a time on the higher bank and it did not work. I’ll try doing all of the RAM and see if I get any success. It’s hard to gauge if the ram is making good contact especially since the card sits vertically in the PEB

 

[mbliss11]

I did some more troubleshooting and then just decided to pull chips I couldn’t safely probe while the card was in the PEB. Found 2 bad chips in the first 4 that I took out and still had ram failure in the test. Going to take out the next 4 later this week.

 

[mbliss11]

One more bad chip and we are in business