I had a Space Shuttle that was working, but lamps corresponding to IJ7-9 were extra bright and staying on when they should not. I changed out the MOSFET IF9Z34N at Q30. (This was a while back so unfortunately I do not recall what the previous Mosfet was testing.). I had upgraded this section of the board per VID1900s thread with Mosfets and zero ohm resistors. The game worked great and only recently developed the brighter lamp column.

When I plugged in and turned on the pin only the GI came on and the game would not go into attract mode. I switched the on/off switch fast a couple of times and it still would not boot. Interestingly the lamp column IJ7-9 would flash VERY bright when operating the on off switch. No other feature lights would operate. On the board the LED would flash 7 when I would switch the on off switch fast. As an aside I also replaced 7408N at u53 and replaced as I had accidentally damaged it the previous chip when removing. This produced no changes.

So prior to replacing the Mosfet the game booted and played, but not now. I could use some advice on what next to test. I have checked the resistor behind the PIA and it tested ok. (SR4 I believe? The game is not in front of me at the moment.). Should I check PIA next next? What results should I see on my logic probe? I can post a schematic in a bit. Thanks

This is the part of the schematic I am referring to. I assume the PIA is the next thing to test. Should pin 17 be pulsing high low? Any input is appreciated. Thanks

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I am an idiot. I forgot to have the coin door open when cycling the on off. Goes into attract and starts just fine. However I still think there is something up with the lamp matrix. The lamp column IJ7-9 is still to bright. The game does not light the correct lamps to spell "tilt" and "space shuttle" correctly. Still looking for advice.

Q22 is testing good. Sorry that was not in my original post. U53 was replaced with new as noted above. I tested it anyways... Pins 4 and 6 alternated high/low very fast. pin 5 always high. I believe this is correct? Pin 5 is the blanking signal which should be high and the PIA would pulse the voltage at pin 4 to bring it down from 18v to 6v? Correct me if I am wrong here.

Finally getting back to posting this just to finish up the thread. I tested Q22 again this time with my logic probe. Definitely pulsing differently than the adjacent transistors, indicating it was bad. Funny when I tested with my multimeter I remember it testing within spec. In any case the logic probe indicated it was definitely bad. I replaced it and all is working well.