I just got a non-working Space Invaders. I turned it on and checked for voltages everywhere. All the boards have +4.1, so I moved to the power supply. this is what I found:
TP1 +7.67 (Supposed to be 6.5 on -49 board) controlled lamps
TP2 +205 (+230VDC) displays
TP3 +9.91 (+11.9VDC for +5) for boards
TP4 +6.1ac (+7.3VAC) gen ill
TP5 +44.3 (+43VDC) solenoids
I'm aware that low voltages (4.1) at the boards can be caused by a bad power regulator on the SDB, but given that it's only being fed 9.9 instead of 11.9 (TP3), I think that may be the issue. I've heard that if TP4 is out of spec, and it is, that the transformer may be bad. The odd thing is, When I tested the F6 fuse holder for 115, I found out that with J1 and J3 disconnected and the fuse in, which is the correct 3A slo that doesn't blow, that I can't find a voltage on either side of F6 fuse's holders, but if I take out the fuse I can suddenly measure 116.5 on one of the fuse holders. The other fuse holder traces to a J2 blue wire that goes to the power switch. Interestingly, with the F6 fuse out, the voltages at the transformer return to normal. 7.3 for instance for TP4. I've verified with online pictures that the J2 connector wiring and the wiring to the back of the power supply board (as2518-49), is correct.
Shorted transformer or power switch? Where does the 116.5 go?
Any suggestions would be greatly appreciated.