1040 STFM screen issue

[jhigant]

Hello there!

My 1040STFM has a strange issue. After switching it on the screen shows almost immediately as in the attached picture. After some time a reset will yield a completely white screen, so temperature plays a part in this. This phenomenon is reproducible. As you can see on the second picture there where some issues at some point in history with the ram memory. I assume this was fixed in the factory: the machine was sealed when I bought it. They did a sloppy soldering job though, looked like some pins weren't attached to the motherboard at all. A small miracle this has ever worked.

I reseated all socketed IC's, soldered ram decently, measured connectivity on all pins of the two rom ic's. No difference. Unfortunately I don't have a scope or logic analyzer, but with some clues as what to check I will go see a friend with decent equipment. I suspect the memory IC's, but I'm not sure.

What could be the issue, and what is wise to check?

Thanks in advance!
Vic.

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[rubber_jonnie]

That screen looks very much like you've got a RAM problem.

I'd tweak the PLCC sockets for the MMU and GLUE using this guide: PLCC Contact adjustment as sometimes cleaning is not enough.

Ideally I'd suggest a diag cartridge and a serial connection as they are pretty good at revealing which bits are problematic, but I'd also suggest either feeling the RAM/MMU/GLUE for what's getting hot or using freeze spray one RAM chip at a time, and if that makes no difference, freeze spray the MMU then GLUE to see if that helps.

If you reset between each freeze then you may get a different result.

If you have a friend with good kit then check all the clocks are good wherever they need to be and that /reset and /halt are not doing anything odd, do continuity checks of the address and data lines, check for stuck bits on address/data lines and make sure cas/ras lines are behaving as expected.

I'd also recommend using a bench PSU to provide 5v for testing in case the PSU is iffy.

Good luck.

[jhigant]

Thanks for all the advice, will do!

Cheers,
Vic