Possible cause:
There might be a loose connection!
Check the connection of the plug J1 on the main board (see picture).
Check the voltage on this plug while running:
white -> black = 0.5 – 1.0 VDC
green – > black = 15 VDC
brown -> black = -15 VDC
If you don’t have 0.5-1.0V, please check the wiring of this cable, which goes to a small board inside the of the PM HF.
NOTE: Check this plug only when the unit is switched off and discharged!