Attach for reference you will find the block schematic made regarding the Transmitter ON command and the 120 Hz require from the Power Supply Board 1-2 to enable the power ON in the transmitter. Below the required signal levels to enable the Power Supply Board 917-0315-001 and turn it ON with B+ voltage, also attach power supply schematic:

TRANSMITTER ON or PS ENABLE J3 Pin 1 = 0Vdc
This is on the 24 pin Molex connector, this will allow the PS ENABLE to Ok condition. Refer to attach Transmitter ON command being sent from the Controller board to the Interface pcb which this will split the signal to each of the 5 power supplies on AM-5E, AM-6A and AM-10A models.

PWR SUPPLY CONTROL J3 Pin 9 = +5V

CARRIER CONTROL PWM J3 Pin 5 = +5V
This has to be a square wave signal which as you increase the power level in the transmitter the working wave cycle becomes longer. You can also measure this signal at the Controller Board's test point TP11 & TP7, this controls the power output on the power supply, normally should measure +5V when Tx is running at full max 10KW power level and controlling the power supply.

POWER SUPPLY FAULT J3 pin 4 = 0Vdc
The controller gets a signal from the power supply J3 pin 4 that indicates that there is a power supply fault, this shows up as a red indicator on the control panel. If 0Vdc, will have to trace back from 24 pin harness #212 thru the ECU Motherboard to the final destination on the Controller board.

120Hz SIGNAL J3 Pin 8 = 120Hz signal or +4.4Vdc
On the Controller board it can also be check at TP12 using an Oscilloscope, refer to 120Hz circuit pdf.

AC OK & ENABLE SIGNALS at U12 Pin 1 & 2 = +15Vdc

These are all the required signal inputs the power supply needs in order to run, strongly suggest to trace back to the Controller Board to find out where any of these signals is being dropped.