Hello.
I have Space Shuttle that has sat dormit for 20 years. My power supply is good. I am getting 4.9v traveling down the grey wires to the board connector. When I plug it in at 1J17, the logic power drops to .3v. My 12v is fine.. Everywhere on the +5v circuit is .3volts. I have replaced all PIA chips, U11, U43, u55, Q51, D2, D3, and resoldered all the pins at 1J17 and have replaced all the canister capacitors in the circuit. Still nothing. Nothing at the LED. Board had some minor alkali corrosion but didn’t destroy anything from what i can tell.
Im attesting my power lost to a short. I can’t find it. I used an infrared temp gun to look for hot spots.
I found a 6 degree higher temp at u55 so I removed it.

Areas that I have concerns that might be a cause

I noticed that
Connectors 1J1 and 1J2 May have some corrosion underneath that I haven’t addressed.
Could relay K1 have an internal short in it?
Several of the SR networked resistors are not reading to spec. Can those directly short to ground?

I am at a lost with what to do next. I am ready to start cutting traces to isolate different areas of the board to try to narrow down where the trouble is. From what I remember playing the game 20 years ago, the airlock door was acting up, and a flipper was getting weak, and a constant drone hum from the speaker during play, so bad that I disconnected the speaker wire.
Thanks for any help anyone can lend.
Matt

I have 5volts (4.93v) from power supply. I get it through the grey wires to the connector. When I plug the connector onto 1J17, the voltage drops. I actually got the voltage up to 2.5 volts. I started removing everything between L2 and Q1-Q5, several of the caps and I have severed the 5 volt traces to the rest of the board. When I turn power on, I get 2.5 volts at 1J17, and even though I have severed all traces that feed the whole board 5volts, several ic chips are showing .5volts and or .3volts at their +vcc pins.
I have disconnected the 12v by removing L1.
When I removeed L2 completely, I get 5volts through the pins at 1J17 and to the first soldier point of L2. I made a jumper to the other soldier point of L2 and the voltage dropped back to 2.5volts. When I cut the jumper wire. It goes back to 5volts.
Before I started removing several transistors, caps, and resistors, all I was getting at 1J17 was .3volts anywhere on the 5v traces.

Those pin connectors where awful. I have removed the pins and cleaned the surface and reflowed the soldier. Have left the pin ps off for now.