Thank you for providing this awesome resource. I am brand new to the hobby, and dove in with 2 early 80's Williams games. Firepower and Comet. My electronics experience is limited, but I have a decent technical aptitude and know enough to get in trouble (and even enough to get out of trouble sometimes.)

Current problem: Comet center ramp lower switch(#50) is not responding.

I have checked the switch and confirmed continuity back to 1J8-8 and 1J10-8. All other switches in the row are working, but the only other switch in the column (playfield tilt #49) is also not responding.

According to Hawes in the System 9 Troubleshooting Guide, I should examine the 2N3904 at Q13 and possibly the 9R 10-pin 4.7K ohm SIP at SR8. The transistor is 50 cents, and I assume the resistor SIP won't break the bank either, but I'd like to understand how to test this circuit rather than just swapping parts.

(1) Does this strategy make sense? Is the SIP likely to be bad? Should I just swap out the transistor or both parts while I have the board out?

(2) Is there an easy or proper way to test these components inline?

Thanks in advance.

Thanks for the tip about shorts. I was fairly diligent in my testing of the switches and harness and found no shorts. I'm not seeing an always-on (short) condition, but rather that the switch never registers. I'm pretty certain it's a driver board problem.

The System 9 reference on pinwiki looks like an excellent resource! Off to read now...