Electrical Diagram for the Power Distribution Board

[Al Skierkiewicz]

Chris,
There is a reverse polarity protection device for the power supplies. It is labeled Q12 on the schematic. If that device is open, then I would bet none of the power supplies would come up. There also is a circuit breaker in series with each of the 12 and 24 volt supplies.
If these are very old PDs then there was an issue that a capacitor was too close to the edge of the board. It sometimes would get knocked off and find it's way into another area of the board. These devices are very easy to open up and inspect. Look for missing parts or smoke damage on the board. Also look for evidence of burned circuit traces.