1040ST Video Issues

[Shugyo]

I am looking for suggestions/ideas for troubleshooting video issues  with a 1040ST I recently purchased. In high resolution, there are vertical black bars spaced regularly across the screen as well as "shadows" or corruption on text that is inline with those same vertical bars. In low resolution, the screen is purple and text shows similar "shadows". I will attach photos that illustrate the issues. I have a few ideas on how to proceed but thought to ask those more experienced/knowledgeable to see if anyone has encountered this before or has ideas as to the cause? A couple other notes: The monitor and video work perfectly with my other ST so I do not believe either to be the problem. The connection to the monitor is via a Best Electronics VGA cable. Also, I did check voltage from the PSU with the system running. 5v is measuring spot on at 5.04 volts but 12v is a bit under at 11.45v. To my understanding, only the 5v rail should be relevant here. Thank you.

[ParanoidLittleMan]

Even if voltages are OK, that means not that filtering of them is good. In so old computer electrolyte capacitors in PSU need replacement  for new ones.

I'm not saying that it's 100% that it causes video problem, but fixing PSU is necessary in any case - unless capacitors were replaced already in last years.

 

And those bars in monochrome mode might be corrected by setting horizontal phase and width on monitor.

 

[Shugyo]

Thank you for your suggestions! I will try the monitor setting and will replace the capacitors on the PSU ( and probably the motherboard while I am at it). I am sure they are the original caps.

[Shugyo]

Update - I've recapped the power supply and it's good to have that done. I also reseated the shifter and mmu and gave them a spray of deoxit d5. No to the to the video. No luck with monitor adjustments either. I think my next steps are to recap the motherboard and maybe reflow the solder on the video connector? I am no expert so suggestions are welcome. Perhaps the shifter is bad?

[Sporny Kun]

if it is still pink/purple with a colour monitor, it seems to me that the circuitry for the green is broken somewhere (motherboard ?, connector ?, cable ?)

[ParanoidLittleMan]

Surely is worth to check shifter - and it's usually in socket, so ...

You can check lines with Ohmmeter - green line - from inside to end of cable to eliminate simple connector, bad soldering problem.

Monochrome still looks for me as monitor adjustment - did you manage to change picture width ? That pattern is typical for A-D conversion.

You will never get 100% good monochrome, just close to it, in any case can be much better than current one.