I picked up a non-working 1978 Bally Black Jack project a few weeks ago and I'm finally getting around to it this weekend. Power on and GI comes on but MPU won't boot (solid LED). Disconnected all boards and started with the power supply. Fuses are intact and at the correct values, and all test points on the rectifier board show proper DC and AC voltages.

I now have J3 on the rectifier board and J3 on the SDB connected. TP1 and TP3 on the SDB show only 2.2v instead of 5v. All other test points on the SDB show their correct values. Figure this will be the starting point of the repair journey. I've re-pinned all of the connectors on the SDB and rectifier, but no help.

I'm looking for guidance on what to check next, hopefully something specific to do to hone in on the low 5v circuit (vs. shotgunning and replacing a bunch of parts...I'm not very handy yet with a soldering iron on a PCB). Note: The SDB in this machine is a Stern SDU-100 Revision A (blue masking). I don't have another spare SDB at the moment to stick in there and see if it progresses any further.

Thanx in advance for any guidance...

wayout440 - I've replaced C23 and performed the ground and +5 mods as outlined in the link you provided, but I'm still getting only 2.2VDC at the 5VDC test points TP1 and TP3. What's next....replace all the caps I'm afraid?