Vertical "rolling" from II+ monitor

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Vertical "rolling" from II+ monitor

I have a minor frustration regarding my Apple II+ clone's display output: it keeps rolling vertically and is very hard to set in place.

 

Normally I would adjust the monitor's "V-hold" trimmer (on the back of the monitor) and when slowed down (i.e. it moves up or down very slowly) it'll "lock" or "click" in place, but for some reason this isn't happening now. I've done a lot of troubleshooting lately (colour was gone which I've just fixed) and this has happened again (it's happened before, then for some reason disappeared). I don't know what's caused it to disappear but I suspected the video cable being too close to something interfering or something like that.

 

Basically it's just really hard to adjust the rolling. Any ideas?

 

 

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Assuming the monitor is OK,

Assuming the monitor is OK, you might try adjusting the VIDEO level control (R11). Possibly too low for the monitor to get a good sync.

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I tried that but it didn't

I tried that but it didn't help much.

I had the colour monitor attached when I noticed the issue and suspected the monitor's V-hold potmeter to perhaps be worn/dusty after all these years and casuing this.

 

But then I attached my green monitor and the same problem was there. That monitor is newer and its rear controls have been much more stable (yes, I've used it recently) and upon booting the display "rolled" there as well, very quickly. If the monitors were the cause it doesn't make sense since the rolling was very fast -usually there would just be a little rolling, demanding a slight twist of the V-hold control.

Another thing: when switching between 40 and 80 columns there is a difference; if I adjust the monitor's V-hold to stop rolling in 40 column mode it would start rolling again in 80 column mode. This usually doesn't happen as I can find a V-hold "sweet spot" which works for both modes.

 

What in the computer is controlling this behaviour and are there any ICs I could try exchanging? Hopefully it's not yet another broken trace, but in that case it would be helpful to know where to start and what signal to look for.

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Since you've already found

Since you've already found some broken traces, I'd check around IC C13 (pins 1,12,13, and 8). The first two pins come from B14 - where you had issues before - so start there. Look at the schematic and see if you can follow the Vert Sync signal through to the composite out. These signals are only about 60 Hz so you might be able to see them on your limited o'scope.

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You're absolutely right!

You're absolutely right!

I continued around the same area and some more broken (or nearly broken) traces, particularly around B14.

I've now meticulously fixed them with strands of wire, and the same with several vias which were flaky. I also filled solder in the otherwise empty vias which looked OK to prevent issues from coming up later (the capilary action is very helpful for this!).

After testing I finally covered the exposed areas with clear nail varnish to prevent any further oxidation. As I took pictures along the process I might post a "how to" on doing these kind of repairs, time permitting.

 

The result? It works!!!

The display "rolling" is completely gone and now the display "locks" in place when slowing down the monitor's V-hold control. Both monitors (colour and monochrome) work as they should, and switching between 40 and 80 columns doesn't cause any "rolling" in the other mode.

A nice thing about my 40/80 column auto-switch is that I now have my colour monitor attached to the main video output (back of the Apple II) while the monochrome green monitor is connected to the output of the autoswitch. So for games I'll be using the colour monitor, while for programming, word-processing, CP/M etc. I'll be using the monochrome monitor, and when 80 columns is selected, the colour monitor doesn't get that annoyingly small and blurry text. All without disconnecting anything!

 

Regarding the display "rolling" -was this likely due to a weak (bad contact) V-sync signal?

HINT: I used "Apple Cillin II" to adjust the colour tint, sharpness and other things in addition to checking RAM, ROM etc. Very handy.

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Fuji wrote:Regarding the
Fuji wrote:

Regarding the display "rolling" -was this likely due to a weak (bad contact) V-sync signal?

 

Depending upon the actual issue you fixed, I would say that the V-sync signal was either distorted or possibly non-existent in the composite signal. This would prevent the monitors from synching properly and thus the vertical roll.

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Yes, that makes sense.

Yes, that makes sense.

I've learnt a lot from these repairs, and of course it's quite rewarding in the end to get such a nice computer working again!

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