Troubleshooting missing colors

beerbarrel

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Anybody ever troubleshoot a missing color output from a PCB? I'm missing green from my Operation Thunderbolt. I'm curious as to haw hard it is to repair color issues. It's not the monitor btw...that has been verified good. I could use a schematic if anyone has one available.
Thanks,
Tracy
 
Well, the easiest way (without a schematic) is to trace the green wire from the monitor connector back to the PCB connector, then try to measure the green voltage (about 2vdc) at the pad. Then follow it back to see if you can find where it is missing. Most PCBs will have a color processing chip not too far in where the RGB is generated for the monitor. If you have red and blue there, but no green, the chip might be bad.

Usually, I'll see some obvious damage like a burned pad or a scratch on a trace that is the cause of a missing color...
 
Schematics (not mine, and I have no connection with the seller):

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=390187639010


I would trace the green signal from the PCB edge connecter back to the first component. I would expect it to be a transistor. Test/replace that transistor. If it checks out or replacing the transistor makes no difference, trace back until you hit a color PROM. Using a logic probe, verify all the inputs and the outputs that make green are all toggling.

Tracing the path of one of your working colors may be a helpful comparison to figure out what is wrong with your green.
 
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