Calibrating 13" AppleColor High-Res Monitor

[Xernicus]

Hey there! I feel that it's somewhat lame that my first post to the 68k MLA forums is to ask for assistance, but "it is what it is" I guess.

So here's what I've got going on. Earlier this year I was gifted a (1st generation mobo) Macintosh II, along with a 13" AppleColor High-Resoluton monitor. :ii:
The Monitor is being driven by a Macintosh II video card, with the VRAM upgrade allowing it to display 256 colors.
Everything seems to be running nicely and within specification, but there's two issues with the monitor that are driving me somewhat crazy.


The first issue is that the raster seems tilted. On the upper left-hand corner of the raster, there is a 1cm blank space towards the north. In the middle, there is 1cm of blank space towards the north. On the upper right-hand corner, that blank space is around 0.8-0.9 of a cm towards the north. The measurements are all equal on the bottom (south) edge.

Now if we were to focus on the east side at the top right-hand corner, it folds in the west direction ever so slightly at the very top (North), and there is some horizontal convergence fringing. And that brings me to my second issue...



The second issue is with the vertical convergence. In the upper left (northwest) area of the raster, you can see a slight blue fringing towards the right (east). In the lower left area (southwest) of the raster, there is a red and yellow fringing towards the right. Now in the upper-right area of the raster, the display is perfectly calibrated in terms of . In the lower-right area of the raster, there is blue fringing once again, towards the left.

I've followed the convergence calibration steps in the Service Manual with the Display Service Utility, in addition to those outlined in "Macintosh II Upgrade and Repair secrets" with a version of TPG dating from '88. I couldn't get any of the pots on the 'H' board, 'B', or 'D' board to fix this problem. And at this point, I've spent so much time trying to correct this, that I figure that anymore "tinkering" will result in more harm than good. For the most part, the convergence is fine too-- the problems are mainly at the edges, and is the worst towards the bottom of the display (where V.BOTTOM would adjust the horizontal convergence... except that's fine).



My theory is that after nearly 30 years, the yoke is in need of some adjustment, but I've never worked on the yoke of a color CRT.

I would really appreciate it if someone could give me a good starting point and some additional steps to correct the vertical convergence. I would be happy to provide some macro photos of this fringing if they would help determine the root of the problem.

Thank you all so much in advance!

 

[techknight]

pictures pictures pictures. 

Cant begin to diagnose the trouble without pictures!

A weak CRT, or a bad degaussing circuit can cause the issues you describe. Weak CRTs cause astigmatism issues, which throws the convergence off. 

 

[Xernicus]

You need pictures, you got pictures. I can take some with a test pattern displayed as well if that would help.

So starting with the upper left corner, you can see the fringing near the top corner of the raster, near the apple menu:

And then the upper right corner... there seems to be no folding in this image, but it does show the "tilt" to the image... I think:

Now we've got the lower left with the red and yellow:

Finally, the lower right which shows the blue fringing along the right edge of the raster throughout the lower half of the display:


Now I forgot to mention earlier that I can get one side in adjustment (let's say the blue fringe on the right). But then the fringing on the left is worse, and so right now I have the pots dialed in to a "midpoint" somewhat. Both sides have fringing- but it's better than having one side of the display noticably worse than the other (at least in my opinion)

Thanks for your quick reply and some "food for thought"!

 

[CelGen]

So it's even at the bottom but not at the top. I'd suggest looking into the trapezoid controls but you won't have those. You can loosen the yoke and see what a few twists to the left or right do but I wouldn't touch it if there's at least something that is level and aligned.

 

[techknight]

The convergence adjustment rings are in the back of the CRT. You can try adjusting those around and see if it helps. But likely the CRT has aged and convergence has drifted. The mis-alignment is so minute, its not really that bad. 

 

[Xernicus]

The mis-alignment is so minute, its not really that bad.

I'm thinking that's the answer I needed. I have an astigmatism and wear correctional lenses for it- so things like color fringing can really bother me sometimes. It's good to get a second opinion.

I may have a go at adjusting the convergence rings later on, but for now I'm content enough with the adjustments I've made.

Thanks for your time and effort.

Happy computing, everyone!