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Old 26th Nov 2019, 8:22 pm   #1
Retrorepair
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Default Computer monitor focus issues

Hey guys, me again

I have a small 13" AOG "Spectrum series" vga monitor which more often than not starts up with reall poor focus but gets better over time, however sometimes it will start sharp and lose focus.

It's really odd behaviour and I can't work out what it could be, it's otherwise fine.

My first instinct was caps with poor esr (often my go to assumption as you'll have noticed, often correct though) but the random behaviour.. I don't know.

Would anyone hazard a guess what I may be looking at?
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Old 26th Nov 2019, 8:55 pm   #2
Maarten
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Default Re: Computer monitor focus issues

Maybe the tube socket or the focus pot (integrated to the LOPT).

The brand is probably AOC. For reference to possible known faults, you could look up the model number and possibly FCC ID, both on the label on the back.

AOC is a brand name owned by TPV, it may even be the name they started under - I haven't found out that piece of early (for Taiwan anyway) history.

Last edited by Maarten; 26th Nov 2019 at 9:08 pm.
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Old 26th Nov 2019, 9:00 pm   #3
AC/HL
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Default Re: Computer monitor focus issues

Does it have a spark trap of any description?
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Old 26th Nov 2019, 9:05 pm   #4
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Default Re: Computer monitor focus issues

That's probably in the tube socket.
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Old 26th Nov 2019, 11:00 pm   #5
cmjones01
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Default Re: Computer monitor focus issues

I had a VGA monitor, branded Viglen but could have been made by anyone, which suffered a related problem: the picture would go dark and take ages to brighten up. The cause was a faulty first anode control on the line output transformer. The focus control was also on the line output transformer, so I'd guess it could suffer a similar problem. Does tickling the focus control make a difference?

I scrapped the monitor rather than trying to find a replacement transformer, but that was in the days when these things were worthless.

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Old 29th Nov 2019, 2:52 pm   #6
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Default Re: Computer monitor focus issues

This fault is going to be very close to the focus pin or LOPT as others have said. It won't have anything to do with capacitors in this case.
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