Completely bizarre monitor problem.

[CHoaglin]

Folks, I have a CRT which is doing something truly strange.

Some text is displayed on the screen.

The top 2/3 or so is displayed pretty much correctly, though somewhat
stretched.

The bottom 1/3 or so is displayed upside down and backwards. In fact it looks
as if the text at the bottom of the screen actually belongs at the top.

I've checked that the yoke is plugged in correctly already. The connector is
keyed and only goes in one way.

If it was a regular monitor I'd just toss it, but it is a 4 or 5 inch CRT
embedded in a piece of process control equipment.

Any ideas what might be causing this sort of behavior? I can take a screenshot
and forward it to interested parties. Does this sound like some sort of bad
deflection IC, or is it likely to be a passive issue (ie: cap job)

Thanks in advance.
-Chris

 

[Sam Goldwasser]

choaglin@aol.comnfgspam (CHoaglin) writes:

Folks, I have a CRT which is doing something truly strange.

Some text is displayed on the screen.

The top 2/3 or so is displayed pretty much correctly, though somewhat
stretched.

The bottom 1/3 or so is displayed upside down and backwards. In fact it looks
as if the text at the bottom of the screen actually belongs at the top.

I've checked that the yoke is plugged in correctly already. The connector is
keyed and only goes in one way.

If it was a regular monitor I'd just toss it, but it is a 4 or 5 inch CRT
embedded in a piece of process control equipment.

Any ideas what might be causing this sort of behavior? I can take a screenshot
and forward it to interested parties. Does this sound like some sort of bad
deflection IC, or is it likely to be a passive issue (ie: cap job)

Not having seen what you are describing, my first inclination would be a
bad cap in the vertical deflection output - i.e., a peculiar case of foldover.

Have you actually looked at the deflection current waveform?
`
Does it change with warmup?

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