Oh thanks Tautech I just got around to taking it apart. The only problem i could find on the power PCB was the 6.3A fuse melted. The sense resistor on the output board measured ok. I was afraid the transformer winding was toast too, but it just reads 80m-ohm anyways.
I replaced the fuse and it all works again.
I believe this happened when I tried powering a stereo, that uses a 6V regulator, as a reference for a bunch of op-amps. And I had already seen that when powering it off a single channel, w/ the correct 7806, but some big capacitors missing...the 7806 would be driven low by the op-amps, which is not something I'd expect, but it did/does.
On the day I think it happened, the 7806 was unhooked, and I went to use the 5V CH in it's place, then I noticed I had no more 5V-CH. That was the 1st time in ages I used it. So that's all I can think of. How that wiould burn out a 6.3A fuze tho, IDK.
For ages I've been using Ch1 for the 18V rail, and Ch2 for the 6V ref rail, instead of a 7806, and that works ok. I need to try that stereo with all the correct caps in place, and then the 6V ref should be powered up before the op-amps get going.