Peavey 400R 15V regulation issue

[tdlunsfo]

I looked them over with my magnifiers and they were all good. I subbed in an MJ15033 for the 431 and it's pegging the watt meter now. The 431 is OL base to collector and tests as a diode on my cheap china tester. I dunno..

[J M Fahey]

Are you getting a solid +/- 40V at regulator collectors?

Only if loaded.

Itīs a somewhat weird regulator.

Only -15V is regulated , by the 16V Zener reference into 431 base; 430 is hanging from -15V rail, inverted, using 2 x 1k resistors as NFB

Meaning failure comes from the -15V area, the other rail just follows it.