Mac Classic II Thin Vertical Lines After Recap, Wash

[adamsargent]

Hello!

I'm working on the logic board of this Macintosh Classic II, and the attached image shows the issue I have after recapping, and washing the board. I also cleaned under the EGRET chip, and the RAM chips. I've even switched out the ram chips, resulting in the exact same issue. No chime either. Analog board is definitely working, works with other classic ii boards.

What it looks like to me is that each stripe is an alternating series of correct looking and not correct looking. What I mean is that the first stripe looks like a strip of the normal startup screen, then the second stripe is what you'd find with leaky caps and an unwashed board. What could be the explanation for this? The issue is consistent, on every startup it looks the same.

Help is appreciated!
Thank you!

 

[8bitbubsy]

Could you take a good picture of the logic board? Always handy to be able to see if something else may need touching up.

 

[adamsargent]

Here's those pictures of the board, I've got some messy bodges which I haven't cleaned up yet, those are good and working though. I figure my next troubleshooting task is tracing all the connections to the EGRET chip. I have also swapped all 4 roms with working ones, to no avail. I haven't done anything with the DFAC chip, maybe I should rework that chip? Also, chip U2 looks kind of crappy, but that's all good.

The alternating lines on screen lake me think there's some issue that has to do with RAM, but I'm not at all sure. The reason I think this is because I seem to remember a ram issue causing something like this somewhere on the internet with like a mac plus or something, and the reason that happened was with the way that the computer allocates video ram or something like that. This could be totally off base, of course. I'm not sure what I'm talking about with stuff like that.

 

[adamsargent]

Here's a video of the screen when I hit the reset button. the very beginning and very end of the video shows what it looks like at all times other than startup. within the "bad" lines, there is some sort of activity which you can see. This is, of course, excusing the CRT refresh rate not matching with the camera and causing it to look weird.

I've traced most of the connections from the EGRET chip, those look good, I think my next move is switching out U12, U15, and the DFAC. I don't like this shotgun approach, but my understanding of the circuitry is rudimentary to the point Where I feel this is my best option. As long as I don't completely mess up anything while using the hot air to do these.