I've got a Stern Galaxy (my first/only pinball machine) with a problem for which I cant seem to identify the root cause. Specifically, the game's left and right outlanes have a rollover star button target that awards either 5,000 or 10,000 points, and each says "10,000 points when lit" on the playfield. The light is supposed to be lit if spot targets elsewhere on the playfield have already been triggered (left outlane needs one target hit, right outlane needs a different target hit). The problem is the outlane star button target lights never light up, even when the conditions have been met to award the 10,000 points. However, the star targets do in fact seem to award properly the 5,000 or 10,000 points, as appropriate, when I look at the score counter scores. So the switches seem to be fine, and the logic seems fine, and its scoring fine, its just that the lights never light (neither the left nor the right lamps ever light).

Here's what I've done so far -- I've swapped the lamps and tested continuity at the lamp holder. I've also confirmed the wiring back to the lamp board is good, and the connector and the pin on the lamp board seem good as well (in terms of connectivity as verified by multimeter). Also, I've eyeballed the transistors on the lamp boards associated with the two outlane lamp circuits in question and they seem sound, but I've not yet tested them (not really sure how in fact, I think I'd need a logic probe, possibly?). I've also pulled the board and looked at the back and don't see any obvious damage to the circuit flows.

Any suggestions for next steps on what to try next? Thanks very much!

Thank you so much!! This both extends my knowledge with these things as well as gives me a path forward for testing. I’ll try your suggestions and reply back with findings.

Well I performed the troubleshooting as suggested by Quench and this seems to very clearly point towards the SCRs as the problem. All other tests illuminated the targets in question, but when applying a jumper to the gate middle legs of SCR Q28 and SCR Q13 neither target illuminated. To insure I was doing this test correctly I tried the same procedure with another, unrelated SCR gate lead, and I could get the appropriate associated lamp to light. So, I'm assuming replacing these two SCRs is in order, right?

Quench do you (or does anyone) know the right part number to order from Marco or some similar such place for appropriate replacement SCRs? I believe this would be listed on the Stern 1981 parts catalog, but I do not have one of these. The wiring schematic I have for Galaxy is annotated to give the part number for some of the SCRs on the lamp board, but not for SCRs Q28 and Q13.

Thanks again!

Great, thanks again and I'll post back again once I get new SCRs in place, hopefully saying problem solved..!