I did a 7805 replacement once, but I didn’t take any pictures and I sold that one a few years ago. I removed EVERYTHING in the +5V regulator circuit, Q1, Q2, Q3, Q15, Q16, D3, D4, D24, C1, C2, C3, R2, R3, R4, R5, R6, R7, R12, R13, VR1. I believe I soldered the 7805 in the holes for Q3, but only one of the three pins was connected where it needed to go, so I cut the traces from the other two pins and soldered a couple wires to where they needed to go. It worked great, but the 7805 got a little warm. It didn’t ever seem to get hot enough that it would need a heat sink though. Wish I had some pictures. It may seem like a lot of work, but I think it was still easier than trying to debug that old regulator circuit. There is no point in touching Q18 on the –5V side until you are sure the +5V is solid.
I am looking to solve the power issue completely once and for all in the Poly-800. What are the parts that I can order for repair and replacing existing ones?
I listed Q1, Q3, Q16, Q18 and a 7805 for now. Anything else I should pay attention to? Any modern parts are welcome.