SE Analog Board - Picture changing width/brightness, possible loose joints?

[Boctor]

Since I bought it a few years ago, the analog board on my Macintosh SE SuperDrive has suffered an odd problem, where the picture often changes scale/brightness. It happens occasionally when the machine is running normally. The picture becomes brighter, slightly wider, and about 1/3 of the screen (on the left) becomes slightly dim. I believe it also gets a bit squashed, vertically.

If the analog board is moved or tapped even slightly, the screen changes between normal appearance and the messed-up state. The board does not need to be warped or stressed in any way for it to occur. I finally recorded the issue, and I'd be grateful for any expert help on what part of the analog board is causing this. None of the components appear to be loose; I cannot find cracked joints anywhere.

An example can be seen here. I hope the diagonal scanning recorded by the camera is not too much of an issue.

 

[SlateBlue]

I would suspect a cold/cracked joint somewhere. There are a few connections that are the usual suspects, and I think where the yoke connects to the analog board is one of them. It wouldn't hurt to touch it up with fresh solder.

 

[Boctor]

I would suspect a cold/cracked joint somewhere. There are a few connections that are the usual suspects, and I think where the yoke connects to the analog board is one of them. It wouldn't hurt to touch it up with fresh solder.

Unfortunately, I think I tried reflowing that one once already. I'll look at it again.

 

[bibilit]

i will gently tap the side of the analog board with something isolated while running, will help locating a cold solder.

 

[SlateBlue]

i will gently tap the side of the analog board with something isolated while running, will help locating a cold solder.

Meaning something non-conductive.

 

[Boctor]

Meaning something non-conductive.

Yeah, I would think so. I don't want over 1000 volts surging through me.

 

[SlateBlue]

Ah, c'mon. It'll be exciting!

 

[Boctor]

I've checked out the connector for the yoke again, but nothing I've reflowed has fixed anything yet. I'm trying to avoid haphazardly heating solder joints, at risk of breaking something. It seems like a gentle press on that area of the board (Near L1 and the yoke connector) stops the screen from getting weird. Unfortunately, if this gentle pressure is released, the problem persists. I don't see anything out of place or wiggling, though.

 

[SlateBlue]

I would then suspect a cold solder joint in that area.

 

[Boctor]

I'm still looking for the culprit, although my CRT is pretty burnt up as it is.

The good news is that I put a jump wire on my SE/30 logic board and got it to work correctly again! My current soldering iron is big enough that it risks bumping into other stuff, so I will get a smaller one and some more equipment, before I ever touch the board again.

 

[SlateBlue]

That's awesome. I'm always happy to see an SE/30 brought back to life.

 

[Boctor]

Whatever reflowing and re-soldering I've done has stopped the screen from jittering around. Though it's still not perfect, there's at least nothing loose or cracked anymore. I've also fixed the centering of the picture and almost have the proportions perfect. Most of all, I'm not stretching the picture too large or leaving the brightness maxed, avoiding excessive stress on the components.

I plan to replace the ancient, burnt-in CRT when I earn some extra money, but the picture is still good enough to see every pixel clearly.