SE/30 display issues; random pixel artifacts on screen — #3

Post #3 by roj_matt

Source Forum	SE/30 display issues; random pixel artifacts on screen — #3
Category	Troubleshooting
Post Date	Fri, 30 Oct 2015 - 01:17
Original URL	https://68kmla.org/bb/threads/se-30-display-issues-random-pixel-artifacts-on-screen.2900/

Post

apm said:
Flipped pixels like this would pretty much have to be a digital issue. There's just no way an analog failure in the flyback, yoke or CRT would produce clean pixels with the wrong value like this.

If the same logic board works in your other SE/30, then check the voltage levels, especially +5V. Maybe it's out of range and causing glitches on the logic board. On the analog board, the only component I could imagine causing this would be the inverter U1, but even that seems pretty unlikely.

The white pixels track objects on the screen, but don't appear in the middle of the grey pattern on the background. It suggests to me a problem on writing to the VRAM UC6 and UC7 (check the continuity on the address lines perhaps).

Thanks, apm! I'm an idiot. So seeing that you mentioned that it sounds more like a digital problem than an analog problem, I went back and swapped logic boards between my working and semi-working machine, just to double check. The problem followed the logic board. I could have sworn that I tried this bad board in my other machine.... So this really is a digital issue. I will check the address lines and report back.