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MDA display - image squished

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SpidersWeb

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I'll upload a photo later today but I have an amber monochrome display, basic IBM MDA style. I received it because after 20 or so years in a factory it became useless, and now I want to fix it.
I'd like to be pointed in the right direction. I do not have an ESR meter, or an oscilliscope.

What's happening is that the width of the displayed image appears to be about 20 to 30 pixels, is dead center, and it keeps overwriting itself.
Vertical hold and size is perfect.

So C:\> displays ok (a bit condensed, a little fuzzy, but readable) - but is dead centre.
However any lines which contain more than about 4 characters however seem to overwrite each other - so you just get solid blocks going down the centre.

My available adjustments are:
Focus (inside the monitor)
V-LIN
V-HOLD
V-SIZE
Sub-Brightness (turning this up too high results in a 1 pixel line down the screen)

Nothing visible for horizontal. So I figured it might be an old cap that needs replacing? If so where would I look for it? What would this cap be (its job etc)?
There is 3 PCBs - the PSU, back of the tube, and the main PCB. They're all small and contain only a few components each but I was after a starting point. If caps are the wrong place to look let me know too.
 
adjusting focus should fix the fuzzy image.

It seems V blank and H Blank timings are completely off for your requirements so you would do good finding what generates them.
 
It's worth asking if this is a clone of the 5151 display (that essentially has no real sync or oscillator circuit) or a traditional TV type display with its own timebase sync-ed to the sync pulses.
 
I'll have a look further at the PCB when I get home (in a couple of hours) and post up some photos.

I found a photo the original owner posted, it's an ASI HMM-1200. Turns out the ASI HMM-1200 was also labelled as Hyundai, and oddly enough Commodore 1402.
So we actually have a PDF to look at.

http://gona.mactar.hu/Commodore/monitor/schematics/1402_Monitor_Service_Manual.pdf

Circuit diagram on pages 14&15.
 
For those that don't want to view the full diagram / can't be bothered with a PDF.

This is the circuit that I believe controls the horizontal deflection yoke (H-DY at the top), the labelled wire goes to the H-SYNC pin on the video cable.

 
Cheers, I'll start with those. What I may do, as it's rather awkward to test / work on / test etc (I'm rather slow when working with high voltage stuff) - is just replace multiple components in one go - any other components that might possibly cause it?

None of the components looked suspicious. Couldn't see any dry joints.
I don't think there is much need for internal photos with the circuit diagram there, but this is what it does:



This is after typing DIR, you'll see it keeps overwriting itself, but C:> survives as it's short enough to fit.

If I understand what I've been reading correctly, that would mean the yoke isn't getting high enough voltages to move completely left or right and it's oscillating back and forward between the hsync pulses (instead of a single cycle)??
 
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