1

This is on an IBM 5154.

enter image description here

Dark grey next to light grey produces a white line between the two. This is noticeable on a color bar test, but is even worse in SimCity (making the text impossible to read).

enter image description here Note the white vertical line down the center (there's also a bright line to the left of the light grey but it's not as bright).

If I adjust contrast to the minimum, the white goes away, but then brown is no longer brown and the 'light' colors are identical to the 'dark' colors.

enter image description here

Thoughts on what this might be? I might try adjusting the red cut-off and LSB, since I notice it's on the boundary of where red is when I turn the brightness way down.

enter image description here

Here's SimCity with the blue and green cut-off at minimum:

enter image description here


Edit: I replaced ~9 or so electrolytic capacitors on the video board, all of them in the PSU, and tested those on the CRT board (all good). None that had any effect whatsoever.

  • I wonder if a bad capacitor in the monitor could cause this? Or a low quality video cable? – traal Jul 23 '18 at 4:30
  • I replaced all of the electrolytic capacitors in the power supply, but that didn't make a difference. Whatever it is, it's only present when the contrast is > 0. – Sydius Jul 23 '18 at 6:02
  • That looks to me suspiciously like a cabling problem to me. If you can show how the 16 colors of text look in front of a cyan background, that may help clarify things. I would expect the RGBI signal would get converted to an analog RGB signal almost immediately upon receipt, and it looks as though there may be some problem before that occurs. – supercat Jul 30 '18 at 21:16
3

You should inspect red HV amplifier (usually positioned on board that plugs on CRT) there should be some suspicios capacitors.

  • Thanks. I replaced the power supply caps already, but not any others. I'll take a look. – Sydius Jul 24 '18 at 3:16
  • There's a small board directly attached to the CRT. It has one electrolytic capacitor and three of some other kind; I was able to test all four in-circuit and they were all very close to their expected value. I also replaced ~9 or so electrolytic capacitors in the "video board" in the path of the red, green, blue signals. None were bad and it had no effect. None were high-voltage, either, though (~35V at most), so maybe they weren't the problem ones. – Sydius Jul 29 '18 at 23:22
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This is caused by the higher voltage swings needed for high contrast causing the RGB guns to go out of alignment.

It's usually due to ageing/leaking capacitors. As a first step I'd try replacing all electrolytic capacitors. Most hardware of this age is going to have bad caps in it. Replace with quality ones (e.g. Nichicon). You may then have to recalibrate the monitor a little using the pots inside, but with luck it might be work.

  • 1
    Thanks. I did replace the ones in the power supply already (there were two blown line filters), but that didn't make a difference. I'll go ahead and replace all of the rest... – Sydius Jul 24 '18 at 3:16

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