Thanks, Patrick, for your ideas.
The regulator board already has load resistors on it that ensure proper regulation at light loads. The big load resistors in the manual are to prove that the supply can deliver into the full specified load. When the PS failed, I pulled one module at a time to make sure that it wasn’t one defective 500 module dragging down the supply. With all modules removed, the supply still won’t come up properly. Like many other Tek supplies, this is an all or nothing supply. If one of the voltages goes down all the others go as well..
The 3 output voltages are derived directly on the regulator card from the output of its transformer. The voltages that I am getting are proportional, so it seems to me that the output transformer is not getting the proper PWM switched 340V from the converter board.
There are 4 wires -- +8V, Com, +25, -25 that feed power from the regulator PCB to the interface card. I did not disconnect these cables, so there is some possibility that the interface card may have a failed component dragging down the supply.
There are some decoupling caps on the interface PCB (that’s the one that has all the connectors to interface to the plug in modules.