Lost Color on a Vision Pro MTG-1901CN

talmazor

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I'm using a Vision Pro MTG-1901CN monitor with an original cocktail version Ms. Pacman. The game displays properly but none of the colors are showing except blue. None of the color adjustments on the neck seems to make any difference. HELP!!!
 

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Well, first turn the blue down. Make sure contrast on the remote is up. None of the color pots for red and green on the neckboard do anything? Have you checked the video cable? Hooked it up another game to make sure it's not something weird with your game?
 
I had the game hooked up to another monitor, which had a vertical hold problem, but the colors were perfect so I know the game is fine. The pots on the neckboard do nothing. You can turn the blue all the way up or down and the screen does not react, this is the same for all the other neckboard pots.
 
Someone had mentioned that there are chips on the board that control the colors, and they can go bad. Anyone have an idea of where these are?
 
Someone had mentioned that there are chips on the board that control the colors, and they can go bad. Anyone have an idea of where these are?

They're probably talking about the LM1205....location I201. I'd also check the color driver transistors...Q551 drives red, Q552 drives blue, and Q553 driver green. These are on the neck board.

Edward
 
It could be shorted open or shorted closed. Typically , the middle leg will short out to an outer leg. Replace it if so. Transistors are cheap

I personally have no experience with this monitor and it's issues. But I would check the transistors and verify the pots are all working properly

.02
 
Need to check the 3 watt resistor 4.7k
r564 it could be open and Q552 the Blue video Trans
One way to test the trans is swap it with another video Amp
like Q551 to see if the problem moves to the red and the blue is good.
R564 may look over heated, need to test the tube if you got a tube checker.
 
Update:.... tested another chassis on this tube and the tube is ok. Check the transisistors on the neck baord and all have similiar readings and are not shorted. check resistors and all are in spec. hell i even moved this chassis to another tube and same blue. Looking at the diagram the video gets processed by a chip on the chassis. I got the # off of it ,

LM1205N. a quick google shows its a video chip. Any idea where to get one and has anyone had this issue. Chassis is super clean and from one of the last crts made and would like to save it if possible.
 
Could be the ic,try to disconnect the Blue drive at pin 17
is it still all blue?
See if the voltage is higher on pin 17,compared to G and R pin 20,26
All rgb outputs should be around the same voltages,with video test pattern.
Its a common ic check other neck boards for ic to try.
 
Update:.... tested another chassis on this tube and the tube is ok. Check the transisistors on the neck baord and all have similiar readings and are not shorted. check resistors and all are in spec. hell i even moved this chassis to another tube and same blue. Looking at the diagram the video gets processed by a chip on the chassis. I got the # off of it ,

LM1205N. a quick google shows its a video chip. Any idea where to get one and has anyone had this issue. Chassis is super clean and from one of the last crts made and would like to save it if possible.

First check to see what the blue input and output pins are on that chip, then check the voltages on them. Compare it to what is coming out for red and green. There are some diodes, resistors, and transistors between the input pin and that IC that could be the problem also...
 
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