PDP8E 3.75V on Omnibus issue

[Nick Allen]

Hey everyone, thanks for always serving as a great sounding board and 
source of advice!

I have an issue with a PDP8E which has an issue with the power supply.  
The -15V, 15V, and 5V are good, and my Bus Loads board is good, but for 
some reason the power supply is bringing down the 3.75V signal from the 
bus loads to 0V (this is the DC VOLTS OK grey wire from the power supply).

I'm having troubles finding the schematics of the PDP8e power supply, 
also any suggestions on what could be pulling the 3.75V to 0V (tested 
multiple Omnibus backplanes, and bus load boards, so I'm fairly certain 
it's the PSU).

All help is MUCH appreciated, thanks!