Hantarex US250 Power Supply help needed

[Level42]

Picked up the Double Axle cab I had bought some time ago yesterday. As said by the seller it doesn't start up and gives a whistling sound.

The unit is powered by a Hantarex US250 switching power supply. This supplies power to the entire cab, so Marquee TL light, Monitor, PCB and coin door lighting.

When I turn on the power, the TL lights up and works fine. The monitor also seems to work OK (considering the "static" sounds I hear from it). The lighting of the coin doors starts up for a moment, then dies.
This is the same with the Power Led on the supply itself. Ive measured the voltages and the supply seems to start OK initialy and then dies. It also produces an unhealthy whistling sound.

All fuses are OK. Because of the age of the cab (1991) I was thinking about dried up elco's.
When I remove the connector going to the PCB's (the one carrying +12,-12,+5 and -5V) the situation stays the same, so I guess the supply doesn't require a load to start up.

Anyone has some experience repairng something like this ?

I also checked the resistance on the +5V and GND leads (going to the PCB) and this is only 50 ohms...I think this is quite low, but maybe this is normal ?