Classic screen trouble after analog board recap

[cofford]

Greetings fellow 68kMLAers!  I have a Mac Classic that has had a bit of a screen wiggle during network activity and other power draws, so I went through the analog board and replaced (almost) all of the caps.  I've previously replaced the logic board caps as well.  Well...after doing that, the screen wiggle is still there, and the top of the screen is now "folded over", like shown in the photo.  Has anyone seen anything like this?  Any ideas where to start?

Thanks,

Casey

 

[JustG]

Hey Casey,

Have you checked the voltages?  It looks like the screen could use some vertical and horizontal adjustment too.

 

[cofford]

Yes.  5 and 12v look good.  Adjusting vert and horizontal works as it should but doesn't get rid of the folded-over menu area...Reducing the overall vertical area does eventually get rid of it, but only when the area of the screen which is upside-down in the pic above is not used.

 

[elemenoh]

I had a lot of wobble on one after recapping. It was resolved by replacing the 1N4148 diodes at DP3 and DP4.

 

[cofford]

So I checked the voltages again, and after recapping my 5V and 12V lines were low.  Adjusted them properly and the screen wiggle is gone.  Unfortunately, the "folded over" section of the screen is still there, and I haven't found any troubleshooting guide that mentions a problem like this.  Are there any CRT gurus out there who have seen something like this before?  I've tried the rear panel screen adjustment pots/coils without success.  Regardless of adjustment, the upper limit of the screen will not go above the "fold" line.

 

[techknight]

This is known as vertical fold-over and 9 times out of 10 its most certainly caused by a bad capacitor in the vertical output stage. 

If you recapped this already, you need to go back and double-check your work. a cap was either missed, wrong value installed, a solder bridge, backwards, etc.... 

The vertical output IC could be damaged as well, but its rare. 

 

[cofford]

Thanks, I'll give it a good once-over.

 

[cofford]

I finally got around to fixing this.  Found that I had put a 1 uf cap in the CF1 spot.  Swapped in a 47 uf and things are PERFECT.  Woohoo!