No - I'm not good at such things. The only assumption I can make is that the listed voltages - or some of them - assume that the relay is closed.
I know that you have looked at the output from the amps through a scope. I would also verify DC voltage on each amp by measuring wire wrap pin #6 using the chassis as the ground. Ideally you're looking for 0VDC, but not likely to see that. Anything above approx 1.5VDC or perhaps higher is suspect. I expect you'll find no problem - probably less than 100mvDC, but worth checking.
I own 2 of these - neither working when I got them. No relay click. Both had a failed Qk2 relay driver. Both tested good out of circuit on a tester, but failed to close the relay. I believe over time they lose gain and eventually lack the oomph to close the relay.
One also had a failed Ck7, as in the leads fell out, shrunken wrapper and crusty white electrolyte leaking out the bottom.
Access to the solder side is doable, just a pain. Make sure you first loosen the nylon connector sleeve to the selector switch and slide it back on the rod. From the bottom side get as much slack as you can on the wires to the board. Swing the rear panel down over the edge of your bench and remove the screws that attach the board braces to the chassis. Then you cant tilt the board back far enough hopefully to work on it.
First thing I'd do in your situation after assuring that DC offset is reasonable is to replace Qk2 with a 2690. You can R & R that one without disassembling anything. That is if your main interest is just fixing it. But I understand some want to diagnose it more scientifically.
