Macintosh SE wobbly raster (analog board problems)

[GiGaBiTe]

I'm working on resurrecting a Macintosh SE for a customer. Everything has been roses and sunshine except the analog board, which just doesn't want to work.

After getting the machine to actually boot (stuck floppy, stiction miniscribe drive, bad RAM, leaking PSU caps, bad caps on motherboard, etc.) I got it booting and noticed that the raster would glitch and flash bright white lines occasionally. The problem would get worse the longer the machine ran. At this point, I hadn't recapped the analog board yet. I got a picture of the wobbly raster starting to happen:

https://i.imgur.com/W5r9TkB.jpg

During recapping the analog board, I noticed that dozens of the solder joints all over the board had hairline cracks from heat stress, which explained the "glitchy" raster and the white lines. So as insurance, I redid every solder joint on the analog board so I didn't miss any microscopic cracks that my magnifier couldn't see. Unfortunately, it just made the problem worse. Now I have nightmare raster:

https://i.imgur.com/I40ogYZ.jpg

So far I've spent about eight hours with the analog board schematic tracing and testing components, and have found nothing bad so far. The only two components I can't test due to risk damaging them is the TDA1170N vertical deflection IC and the 74LS30N quad input AND buffer. Could these two chips be causing this mess, or is it something else I'm missing? I know for a fact it's the analog board, because I can swap the analog board from my personal SE FDHD in and everything just works:

https://i.imgur.com/VWlTp2Q.jpg

Any help with this problem would be appreciated.

 

[GiGaBiTe]

Not sure what I did, but it got better after reinstalling the old 3.9uF deflection cap, and another cap on the horizontal section of the analog board. I also cleaned the potentiometers and reflowed some still suspect looking solder joints again.

https://i.imgur.com/0YCy9Al.jpg

It's now back to the original random glitching raster, and tapping the analog board while its running doesn't introduce any additional bad behavior as it did previous, so there's still a bad component somewhere.

 

[AndiS]

Reading this I think your Classic Mac Repair skill are more advanced than mine. But maybe I can be of help still ;-)

I had a wobbly screen problem with a Mac Classic recently (connected to disk drive activity). Replacing all the caps, some diodes and the QP1 optocoupler did not fix the issue. In the end the Analog Board voltage was too low, probably due to oxydised potentiometer contacts. Contact Cleaner and new voltage calibration fixed the issue.

 

[bibilit]

Not usual, my best advise is to remove the rear casing and poke around with a wood stick trying to reproduce or stop the issue.

Had more or less the same issue at some point, was a cracked solder joint on the wire coming from the Flyback transformer (under the suction cup, where the two clips are fastened to the CRT) was able to stop the issue with the stick,  soldering back this wire solved the issue.

 

[AndiS]

@bibilit Nice one. That brings up memories of me doing a similar thing with a G3 iMac that was making an incredible loud high pitched noise. Found the source and glued it down with epoxy - that fixed the issue. I had completely forgot about that

 

[GiGaBiTe]

@bibilit My method was to tap the analog board with the handle of an insulated screwdriver. I'm pretty sure all of the bad joints have been fixed because nothing happens when tapping anymore. Initially the tapping would cause bright white raster lines and eventually the machine would crash with a sad mac screen. After all of the reworking, the tapping doesn't do anything anymore. There's still a bad something somewhere. Could still be the potentiometers, or a broken wire in something like you said.

 

[GiGaBiTe]

Well the bad part just revealed itself, the horizontal output transistor just went thermonuclear. Whole house stinks like burning silicon, lovely.

Customer will definitely need a replacement analog board now unfortunately.

 

[cheesestraws]

Well, that's decisive...