shake 33 power amp in protect e01

I have a Sony Shake33.

It is stuck in protect e01.

The repair manual says that it could the main amp board or the power supply. Here is the description: "The overcurrent condition to MOSFET occurs by a defect of MOSFET or defect of PS output line."

So I want to check the power supply first. Since I cannot power up the amp as it disconnects on boot, I can unplug it as it is modular and it boots fine. The test procedure doesn't require high-end testing equipment just a multimeter. The readings on the pins that come from the power supply are all good with the exception of the 1 st pin. It shows -22V when it should be 16V~23V. The actual power supply schematic says "pin1: V3+ (DC+16V~23V) _ (ref-V1)".

My question is what is V3 and ref-V1 from the above formula? Am I testing this correctly?