VOGONS


First post, by Rita's Cafe

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This 15" NEC VGA CRT monitor has recently started exhibiting some strange issues with the picture. Sometimes the green channel is absent other times it appears that the blue and green are absent. More commonly all channels are present but the picture appears dark on the top and bottom halves of the screen with a small horizontal area in the middle that is still bright. See attached photographs for a better explanation.

The issue presents itself after a period of operation. Sometimes this can take two hours to show up. Other times it will happen within five minutes of use from a cold start.

The attached photographs show test patterns in 640x480 and 800x600. Interestingly running “edit.com” in DOS shows the issue but the command prompt appears fine.
All photographs are of DOS applications. The same issues have occurred using a different motherboard and two other GPUs.

Information about the monitor:
NEC Multisync XV15
The RGB amplifier is an LM1203.
Purchased three months ago and worked flawlessly for the first two months.

Hopefully somebody here will recognize these symptoms and be able to point me in the right direction. What is causing this and how do I fix it?

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Reply 1 of 4, by pentiumspeed

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Solder joints breaking. Visually check and resolder all boards. Yes all.

One right location when solder joint break will blow up and burn out possible irreplaceable part.

Cheers,

Great Northern aka Canada.

Reply 2 of 4, by Rita's Cafe

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pentiumspeed wrote on 2021-10-11, 21:47:

Solder joints breaking. Visually check and resolder all boards. Yes all.

One right location when solder joint break will blow up and burn out possible irreplaceable part.

Cheers,

Thanks, I'll try reflowing everything this weekend.

I find it strange that I can switch back and forth between command prompt and edit repeatedly and every time the screen issue will show in edit but not in command prompt. As far as I know, they both run at the same resolution just different things on screen. Perhaps this is a clue as to where the problem area is but I don't know enough about CRT workings to tell. Being that sometimes the green channel is all that is absent is it safe to assume the first board to look at is the board which both the VGA cable and tube connect to?

Reply 3 of 4, by pentiumspeed

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lost color is on CRT board itself, you will see a cracked solder joint. Helps if you have a magnifying glass. And good idea to check the large board that is under the CRT as well.

Problem is, you may have metal shielding covering the CRT board that needs to be removed to see them.

Cheers,

Great Northern aka Canada.