Mitsubishi Diamond Plus 200 insufficient blue

Feb 03, 2011 8 Replies
K

I just got an old 22" Mitsubishi Diamond Plus 200 CRT monitor. The previous owner said that the picture was "greenish". He didn't say anything else about it.



The problem is that the blue color is about one tenth as bright as it sould be, which means the colors look greenish-browning, unless I set the red and green gains down to where I can barely see the image in a normally lit room.



Of course, I tried to set the blue gain to the max setting, but it is still one tenth as bright as it should be, by my estimation.



I opened the unit up and looked inside. It is fairly free of dust. The parts of it that I could see without taking it completely apart didn't show any visible defects such as burned parts, loose connectors, broken wires, scorch marks, et cetera.



Aside from the dim blues, the unit works just fine, and I would like to take a shot at fixing it.



Does anyone have any suggestions for what I should check first, second, third, and so on?



Thanks to all of you.



Graviton.


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S

One thing which sometimes helps, reflow all connections on the board plugged onto the tube.

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N

Try swapping red and blue drive lines. Isolates to the final or earlier stages

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K

I'm not a professional, just an experience amateur, so my tools and skills are limited. Could you provide more details on this procedure?

Thnx.

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K

edited

Also, could someone point me in the direction of a pdf of the service manual that I could download? Preferably for free?

Thnx.

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K

Additional symptom: when it starts up, the blue comes on from the bottom of the screen up, but in less than a second.

Thnx.

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W

Well, I'd start with centering the blue control, maybe the red and green too, then readjust the high voltage "screen" or "G2". You need a grey-bars test signal to readjust the color (first diddle the RGB offsets, to get the darkest bar neutral gray, then change the RGB gains to make the lightest bar neutral).

Some monitors do a lot of this through software, but removing the case back and poking in with small adjustment screwdrivers is the usual procedure. Beware the high voltage (anode) wire; your adjustments have to be made with power ON.

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K

I don't see any hardware RGB adjusters. I've only used the software controls.

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S

It means that the software driver for the blue electron gun needs to be updated.

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