Classic II Vertical Deflection Issues

[SuperSVGA]

I have a Macintosh Classic II (Performa 200) on which vertical deflection was not working. All I got was the bright horizontal line.

After replacing nearly all the electrolytic caps, the video/power ICs, and testing a few diodes, I was still getting the exact same symptoms.

When I checked voltages at the TEA2037, I was getting very low voltages at the Flyback Generator Supply (0.48V) and Frame Power Supply (0.32V).

I tested RL2 which tested to be around 650KΩ, which according to the markings should only be 1Ω. I replaced it with a 1Ω 1/8W metal film resistor and put it back together. Notably, the Bomarc schematic I found online for the Classic I lists RL2 as 2.2Ω, but the markings on this one were clearly 1Ω.


Now when I test it, I get "full" vertical deflection but the picture is unstable, jittering/scrolling vertically.

Turning the vertical size adjustment, I can only get a stable image by vertically squishing it down to half of it's size.


Any idea what's wrong now? I've replaced so many parts in this I'm not sure where to look next.

 

[Johnnya101]

If you have deoxit or something similar on hand you can try to clean the pot for vertical height. Someone else on here had issues and it turned out to be a dirty pot.

Someone else that knows more will probably respond soon, but in the meantime, you can try that.

 

[SuperSVGA]

If you have deoxit or something similar on hand you can try to clean the pot for vertical height. Someone else on here had issues and it turned out to be a dirty pot.

Vertical height or vertical size?
I was thinking vertical height was fine, as when I squish the size down it seems to move around without issue.

I pulled the vertical size potentiometer off and tested it a bit, and it seems to give me a smooth range from about 0.335Ω to 1.923kΩ. It does say it's rated 2.2kΩ but I think it might be close enough.

I could spray some deoxit in anyway, but I can't see any suitable gaps or openings to do so.

 

[SuperSVGA]

Sorry, I got the two mixed up when writing the last post. I tested PF2, the Vertical Centering adjustment, which is a 2.2kΩ potentiometer.

PF1 is the Vertical Size potentiometer (100Ω) which also looks alright. I removed both of them, put a very generous amount of deoxit on both and gave them some turns before drying them off and re-attaching them.

Now I'm back to the horizontal line again, and turning the potentiometers has no effect.

 

[Johnnya101]

Maybe you should check voltages from the floppy port just to make sure it has enough power? I don't know how to do it, but I'm sure it's in a past thread somewhere. That will at least rule out low voltage somehow causing this.

Did you test PF1 as well? If now you can't get at least a small image after cleaning it, it may be the issue.

Edit: I see you said nearly all the caps. Replace them all. That may be related to this. The classics have really bad quality caps and they all leak. Also, look around the flyback area and I would consider resoldering all the pins, also to the video connectors. Don't just reheat solder, remove it then use new.

 

[SuperSVGA]

Edit: I see you said nearly all the caps. Replace them all. That may be related to this. The classics have really bad quality caps and they all leak. Also, look around the flyback area and I would consider resoldering all the pins, also to the video connectors. Don't just reheat solder, remove it then use new.

The only two I have left is the big 220uF 250V filter capacitors on the primary side. I'll have to put in an order to replace those, though they tested fine on the ESR meter when I pulled them.
I'll go over the solder joints with the wick again, but I must say they originally looked surprisingly pristine compared to other analog boards I've seen.

Did you test PF1 as well? If now you can't get at least a small image after cleaning it, it may be the issue.

PF1 topped out at about 115Ω, which is a bit higher than rated but if these are rated ±20% then it's well within tolerance. I checked it again after this issue returned and it still looks about the same.

I guess I'll start just pulling most of the components and testing them individually and see if I can find something else that failed.

 

[Johnnya101]

Oh, if it's just filter caps then you are probably fine. It's just the radials that really go bad. Of course, you should do the filters at some point, but those shouldn't cause this issue.

I think the classics are known to have optocouplers go bad, but not sure if they would cause this. If you search up classic horizontal line, there's a bunch of older posts that may have some solutions.

 

[SuperSVGA]

I think I got it working.

The initial issue seemed to be RL2, which was responsible for passing the VCC voltage from the flyback to TEA2037.
Once this was replaced the VCC voltage (min. 12V) was reaching the TEA2037, which made vertical deflection start working a little, but it was far from functional.

I replaced TEA2037 (the second time now) and everything seems to be perfect now. I'm not sure whether the original one I used was bad or if some sequence of events caused it to fail.