PV Mark IV 16ch head scratcher

[Gtr_tech]

Bought onna these for a giveaway price. Repaired 2 channel strips that were out, still has a problem with the monitor sends sending DC to the meter board, but thats not the part that worries me. I checked the rails to the op amps and I'm getting *twice* what the rails should be......around +/- 30v. These should be 15v rails. Now I've checked the pass x-istor for the +15 (ok) and the 7905 to-3...not shorted. 15v zener is OK, all resistors and other semi's check ok. 4558 op amp was subbed as well. Ground is solid. So aahhh....WTF? The problem is common to both rails so it seems ground integrity would be in question....seems ok to me. I'm about out of ideas here.

Anyone seen this before?

[Gtr_tech]

Fergit it.....I pulled everything out of the flight case and splayed it out on the bench. Ended up be'n the 7915 reg breaking down under voltage and throwing everythring off.

[Enzo]

Glad you found it.

The 7915 is the whole basis of this supply. The 7915 provides the -15, but the +15 regulator circuit is discrete and runs off of and tracks the -15. SO if the -15 goes nuts, then so will the +15.

Schematic is too large to post here. Drop me a line if you want it.

[Gtr_tech]

I have the print for the mark IV board. Just a PITA to t-shoot in the case. Once I marked the component designations on the reg pcb it was obvious. I'll save the "points" for a future use