A buzz in both channels

[Paul Birkeland]

If you had a whacky voltage, then maybe there could be a dead part on one of the PC boards.  Likewise, a failing transformer is going to throw out some odd voltages. 

Loose hardware can also create the problem you're experiencing.

[Skipperrik]

I just checked the resistors on the low voltage board and the 2.47Kohm at the RC position measures 28.9 ohms. This is the opposite side from the one that had the bad regulator. That side measures fine.

What could cause the regulators to go bad?

Here are the voltage figures from the low current board:

IA  150
OA. 64.0
KregA. 4.3
bRegA. 150.1
IB. 169
OB. 63.4
KregB. 1.54
bRegB 168.2

[Paul Birkeland]

Those are not working voltages.  The 1.54V at KregB is no good, and bregB is also not correct.

This can happen if the A side high current C4S feeding that side is shorted and dumping excessive current into the regulator, from a miswire, or potentially from a failed 431 regulator.

The 2.49K resistor does not go in the RC position.

[Skipperrik]

Sorry, I mistyped. It’s the 2.49Kohm resister at R3.

I’ll replace the regulator and see if the voltages straighten out.