I've got quite a few 70s Gottliebs, but a friend bought a non-working Target Alpha that I ended up working on.
I always pull the bottom relay board out and go through everything. Tighten switch stacks, clean and adjust contacts. After all that, I put it all back together and nothing changed. Then had to pull it out again and go over everything again. Still didn't see anything obvious.
Putting it in the cabinet and hooking it all up, it really came down to the AX, DX and their associated reset relays. Between not latching correctly or the switches not traveling enough, I must have spent 5 hours adjusting those relays. I always hate loosening the screws and sliding them around because that always seems to make it worse.
Well, it's finally working now, but what a PITA! I hate those relays! So who's with me?