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Comment by kazinator | Hacker News Reader

> The cruel joke? In business mode, the picture was fine. The problem, whatever it was, manifested itself only in casual mode: the mode all the games used.

Curious terminology.

A high resolution text mode being stable, but a low-res graphics mode going haywire is almost certainly an issue with the display adapter and not the cathode ray tube.

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EGA was "dual-sync": in the 200 line modes, it ran at 15 kHz, whereas the 350 line modes ran at 23 kHz. While it's quite possible that the card had the problem, it's also possible that CRT was the problem. If the components drifted out of spec, it might no longer be able to correctly sync at 15 kHz, especially after warming up.

The problems being described sound like capacitors that have gone bad in the deflection circuitry. In the world of arcade machines, which run CRT monitors for hours on end every day, this failure mode is very common, and it shows as a "curl" on one or more sides of the display.

The tube itself probably wasn't the problem. Trouble with the electron guns usually means a dead tube, or a dead color. Problems related to sweep are outside the tube.

If he had a problem that appeared as overheating, the first thing to try is freeze spray. Find out what component is temperature sensitive. It's probably a capacitor.

It's not that hard to work on a CRT unit. You have to discharge the second anode voltage after powering off. (I was once trained to repair analog radios and TVs. This is now a totally useless skill.)

I'd blace my bet on the deflection circuits (horizontal output transistor). I had similar problems with a more recent CRT, where the top right corner of the image started to shake frantically after a few minutes if you switched to high resolution modes.

EDIT: It seems I didn't catch any of the details right... the author's display was probably not multisync and developed problems in the low resolution mode. Oh well.

With the risk of going OT, I have an deal old monocrome monitor (Zenith ZVM-121) that died on me shortly after feeding it 220 V @ 60 Hz from a step-up transformer. How does one go about fixing such? Are there any place that will still repair them?

I love those remote debugging sessions :)

I have never seen those circuits so can't comment on what could be wrong, but if cooling the monitor helped I think it wasn't EGA's fault.

Too bad the OP didn't keep this machine.

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