Apple AudioVision 14 with rotated raster

[Dennis Nedry]

I used to have an Apple AudioVision 14, and the raster was crooked. It got worse and worse, and let me tell you, it got so bad that you started to hold you head at an angle while using it.

I have since given it to my grandma with a Power Mac 7100 so she can play solitaire... It is being legitimately used, though, so that's good I guess.

Anyway, I have since acquired 2 more AudioVisions which don't have this problem. I have a hankering to swap another screen with hers to get that back so I can swap parts and figure this out. I think this was a common problem, I remember seeing several crooked AudioVisions back in the 90s.

The service manual says to replace the analog board if the screen rotates. Has anybody narrowed down which components on the analog board cause this? There is NO ADJUSTMENT for rotation in this display unfortunately.

 

[Dennis Nedry]

I understand that a possible solution is to simply loosen and turn the yoke, but the underlying problem in the analog board would remain. It tends to rotate even more with age. It must be about 20 degrees rotated to the left right now. It's ridiculous! At this rate it will become a portrait display by 2050.

 

[Scott Baret]

Your best bet is to rotate the yoke. Loosen the screws alongside it and carefully turn it (you'll have to do it while the monitor is on to see where you're turning it). DO NOT TOUCH THE SUCTION CUP-TYPE DEVICE (technically known as the anode cap) UNLESS YOU WANT A HUGE SHOCK!!! You'll need to be VERY CAREFUL while doing this.

I have done this on several compact Macs and often do it with a mirror in front of the display so I don't have to reach around the tube. Don't bother with the analog board unless this happens again over a very short time--in that case you may want to replace it, but as long as you get the yoke where you want it and tighten your screws properly you should be good to go with a non-tilted raster.

 

[Bunsen]

Search CRT discharge here and elsewhere

 

[LCGuy]

There's no adjustment pots in the back of the monitor? I've never worked on an AudioVision myself, but I'm fairly sure that they're supposed to be fairly similar to the 14" Macintosh Colour Display, which does have adjustment pots in the back, one of which is for raster rotation. Worth another look at least.

 

[tomlee59]

First verify that the rotation is not due to a loose yoke. Check for the existence of electronic rotation adjustments, as LCGuy suggests.

If the yoke is not loose, then the drift in rotation is electrical in nature. A 20-degree rotation is somewhat larger than what most such circuits typically provide, but maybe this monitor is atypical. If that circuit has failed, perhaps one of the adjustment pots has gotten dirty, or the DC supply that feeds it has gone south. If the rotation eventually seems to stop changing, then simply rotating the yoke might be an acceptable fix, but without knowing (and fixing) the true cause, there's always the risk of the drift re-emerging at some point.