Repairing an Atari 600 XL upgraded to 64 KB RAM

[rubber_jonnie]

Not even overheating. I've recently encountered a few Antics and GTIAs, and one Sally, which were not overheating, but were crashing over 25-30°C, yet while kept below 10°C they were working fine.

Interesting they failed even at that low temp. The Sally had already died in my own 600XL so needed to replace that before I could even start to troubleshoot the RAM problem.

[stephen_usher]

I've seen a number chips which fail like this, such as a controller in a Sony floppy, which only works if there's ice on top of it.

[mst]

Ok, so it sounds like you have covered a few things here, in that power is good, as is the RAM and there is good continuity with the wiring of the 64KB mod.

I note you've replaced the electrolytic capacitors, however there are a couple at least that are bi-polar, however I don't recall which ones they are. IIRC they are up near the top left end of the board and I think are axial, but it may make a difference. IIRC they have BP written on them.

I think what @tzok is valid too, you need to check for overheating chips.

Yes, there are some non polarized ones, replaced with non polarized too.

None of the chips are hot, mainly all are cold except the Sally,
but its hot is very moderate, it appears a normal temp.


Many users told me that many of the Sally 600 XL CPUs turned bad,
before they were manufactured by NCR, Sinergetic (I think that's how it is written)
and they have seen similar failures due to bad Sally


I will continue troubleshooting during weekends,

[rubber_jonnie]

Ok, so it sounds like you have covered a few things here, in that power is good, as is the RAM and there is good continuity with the wiring of the 64KB mod.

I note you've replaced the electrolytic capacitors, however there are a couple at least that are bi-polar, however I don't recall which ones they are. IIRC they are up near the top left end of the board and I think are axial, but it may make a difference. IIRC they have BP written on them.

I think what @tzok is valid too, you need to check for overheating chips.

Yes, there are some non polarized ones, replaced with non polarized too.

None of the chips are hot, mainly all are cold except the Sally,
but its hot is very moderate, it appears a normal temp.


Many users told me that many of the Sally 600 XL CPUs turned bad,
before they were manufactured by NCR, Sinergetic (I think that's how it is written)
and they have seen similar failures due to bad Sally


I will continue troubleshooting during weekends,

Yeah, as I understand a bad Sally is quite common. My own 600XL had a bad Sally (I don't recall the manufacturer) and got very hot when powered on.