WG 27K7501 green cuts out

debaser138

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I'm working on a WG 27K7501 medium res monitor that runs but the green will completely cut out. I'm using my TPG to put up RGB color bars and the green bar will go completely black. When it's cold the green will go in and out but after awhile it just goes out completely. I can power cycle the monitor and the green comes right up but after a few moments it's out again.

This neck board had jumpers run for all the color transistors traces since they were burnt up (arcadecup had done work on it a few years back). I reflowed solder on the transistors for the green circuit. I ohmed out all the traces and they are good. I tested the transistors with my DMM and they test fine as well. I also tested the tube and the green gun is fine. I tested the harness from the neck board to the main board and that is good as well.

I'm thinking it could be the LM1203 is failing after it warms up. I need to order one (along with some 2SC3782's to have on hand) before I can dig any deeper into it.

Anyone seen this before?
 
Last edited:
Well, it looks like the tube may be the problem after all. I hooked it up again to my B&K 467 and the heater leakage lamp and the G1K short lamp were coming on when I put it in restore mode. I tried removing the short a few times and now the G1K short lamp flickers on and off. If I lower the HTR voltage, it goes out.

I let it cool down and then hooked the chassis back up. When I fired it up the screen was good for a second and then I heard a crackle in the CRT neck and the screen colors went all weird. Powered it down, fired it back up and now it's working great. Red, Green and Blue all look good.

Looks like this tube may be on it's way out.
 
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