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Segai M21C XX hourglass screen

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I have a segai M21C XX CRT screen that has the "hourglass" look. The left and right sides or "curved" inwards
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According to a manual that I have found (, there is a "East/West Correction" pot on the board VR203. I have tried to turn the pot completely left or right or somewhere in the middle, but this has no effect at all on the actual image.
Could this pot meter be defective? Or is it somewhere else? Any idea what could be wrong?

Your problem is commonly called pincushion distortion, or, as you've identified, East/West correction. It's normally corrected by an adjustment to the horizontal output circuit. However, that schematic you present has the components in the horizontal section starting with the number "3", so VR304, C302. It's the ones in the vertical section that start with "2", and you say you're playing with VR203?

I may just be raising this because i cannot even find VR203 on that schematic :D Can you point out where it is, please?

I'd look at the stuff around the LA7851... capacitors and resistors. it handles horizontal and vertical drive synchronization.

if you check out the datasheet for the LA7851, you can see what pins on the chip do what and focus your search for bad parts in these areas. (out of spec resistors or dried out capacitors.

Many thanks for your replies.
When you talked about pincussion I noticed there is a pot for that too VR304. With that I was able to correct the problem.

I have another problem with this screen I would like to address. There are at the sides of sharp lines some kind of "outline" lines. They usually have the same color as the original line, but with much higher contrast. It's like all graphics have some kind of "outline" in higher contrast to them. This is perhaps best explained with the help of some images I took.

When I lower the general brightness, the effect becomes much more prominent. Giving the screen more contrast and brightness lessens the problem a bit but not to a "normal" level.
Any idea what this problem is called? I was thinking about convergence, but not sure that it's the case. Also I noticed my tube (Segai) does not have any convergence rings at all.
Many thanks for your help.

I tried to hook up a real NeoGeo console with Metal Slug and there the picture is perfect. So it probably has nothing to do with the monitor, but with the PC. I tested on a mame PC running emudriver and groovymame.
I asked this question in the groovymame part of the forum.
Many thanks


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