Response from Jonathan: Eric,

There are several different things that might cause a missing color issue like this. For one, you might try checking the input wiring that runs from the Ms. Pac Man board to the monitor chassis itself. Start off by tracing the video blue wire that run from the harness to your monitor chassis to see if it is making a good connection. According to the Ms. Pac Man harness pinouts, this wire should be located at pin U (pin 17, parts side) on your harness. You can use the continuity check on your multimeter to see if the wire has any breaks in it. Check out our post on Checking Fuses With A Multimeter for more information about continuity. If the wire is making a good connection, you might try touching up the solder on the back of the blue input pin on the monitor chassis. These input pins like to come loose sometimes especially after years of unplugging and plugging in the connector.

If all the input wires are making a good connection on both the harness and the monitor connector ends but the problem continues then you may have an issue with a color drive transistor. It could be that your blue drive transistor is acting up on your monitor and needs to be replaced. It could also be that the blue gun on your tube is not working properly Check out our post on Checking A Monitor Tube for information about both of these issues.

Hope that helps. Thank you for your question and good luck with your repair.