kortex monitor color slowly changing/shifting

starfighter2

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I have a kortex monitor that looks ok, but the colors seem to shift to another color. The yellows for example will slowly shift to an orange and then back again and reds will shift to a different color or red/orange and back slowly and so on. Other than that the colors are bright but something is deffinetly not correct.

I have tried a couple of other boards with this monitor that seem to work fine on another monitors. There is a bob roberts cap kit installed already.

Anyone see something like this before.
 
I've seen an issue where some large (30"+) direct-view CRT TVs will discolor on static bright images, shifting from white to blue or orange gradually the longer the image is up. (I have an old Magnavox TV with this issue.) IIRC it was caused by tired phosphors losing their even response as they warmed up. That doesn't sound like your issue though -- red wouldn't shift to orange.

Can you reproduce the problem with a test pattern, just to rule out a quirk in the game? Let it sit on a solid red for a while and see if a pattern emerges.
 
I can try a test patern, but I have tried this board on other monitors with no issues. So I don't think it is a game issue. I also tried 2 different games with the same result.
Any other ideas on what to check?
 
I can try a test patern, but I have tried this board on other monitors with no issues. So I don't think it is a game issue. I also tried 2 different games with the same result.
Any other ideas on what to check?

Part of the point of the solid red is to see if there's a pattern to the discoloration. It may be a clue.

You've set me on a tangent researching CRT technology. I'm gonna learn something today!

-E- Okay now, I think I have a pretty clear picture on how CRT discoloration happens. Two possibilities:
  • One, it's possible this is being caused by something in the chassis; specifically, a board fault may be causing the color driving circuits to drag each other around a little. This should be pretty easy to test for, if you have a schematic and are comfortable probing a powered up chassis. Watch voltage on green/blue circuits when on a solid red screen.
  • Two, your shadow mask/aperture grille may be very slightly magnetized, causing the beams to get diverted just a tiny bit. If that's the case, the fact that it fades in and out is probably caused by the mask/grille expanding and contracting slightly due to temperature differences. (It might even be a kind of feedback loop -- beam heating up mask, mask expands, more of beam going through mask instead of hitting it, mask contracts, more of beam hitting mask.... to that end, I'd check to see if it behaves differently while cold.)
 
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