John wrote:

There's a daughter card, who rectifies the main AC: the voltage across the two
big caps is correct.
Across source and drain of the TOP200YAI - Three-terminal Off-line PWM Switch
there is the rectified voltage. The control input is 0.

On the control line of the opto is not 0, but 0.34V.

It seems that the PSU lacks the "start signal".

You have a power good wire "PG" and a start wire "GREEN" which as to
be pulled to common.. ALso, depending the vintage, you may not have a
"GREEN" wire..

I don't remember the color code for the PG line, I think it was Orange
but don't quote me on that one. It'll be in the main bundle to the
PC board, not any of the hardware power connectors.

Jamie