520STfm blank green screen with intermittent blue lines... what?

[MayorDefacto]

This has got me stumped. I recently purchased a 520STfm from a guy on Craigslist who said it "worked the last time he used it." I also scored an SC1224 monitor (one of the Goldstar monitors with the hardwired cable) for $7 at a thrift shop that same week, which was a massive steal as far as I'm concerned.

 

I finally got some time to mess around with the two items a couple weeks ago. The monitor was seriously maladjusted, but after about an hour of fiddling with the pots on the back, I got the image to stabilize and sync. The monitor, now that it's adjusted, appears to work great, but now that I can see the image from the computer, I'm wondering what's wrong.

 

I get a solid green screen with a series of cyan-blue lines running in parallel down the screen (I've attached a couple images to show what I'm talking about-- apologies for the phone-pic quality). No bombs, but just a green screen with some weird lines. I've also noticed that the disk drive doesn't seem to make any noise or recognize any disks, so I'm not sure if it's dead or not.

 

I did completely disassemble the 520 and manually pressed down on each socketed chip, thinking maybe the ROMs had come unseated. I did not, however, completely remove the ROMs, clean the pins and sockets, and reseat (maybe I should have?) The issue persisted even after I did this.

 

Any ideas what could be causing this? The possibly-faulty disk drive? ROM troubles? Some adjustment on the monitor that I neglected? Something else I haven't considered? I'm hoping someone has seen this issue before and knows what's going on...

 

Thanks in advance

[Fuji-Man]

I'd pull chips again, check legs of chip for discoloration.

remove floppy? check ram?

power supply look okay? might need recapping.

If only you had a diagnostic cart, that might help.

[GadgetUK]

Could be a DRAM fault.

[tjlazer]

You could try the 4" universal drop to see if that helps. But since you pressed on all socketted chips not sure.