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There are any number of things that could be wrong, 280 volts would definitely upset the camera PSU, so the main psu needs fixing first.
The main ht supply comes from the transformer and bridge rectifier in a conventional fashion. This is then fed to the regulator, a simple chopper SCR, control is on the PCB and SCR on the heatsink below. Use a light bulb as the load and get it about right before inserting the camera PSU, It may be the main PSU will run without the camera PSU present, but you may have to fool the regulator to run without the feed back from the camera. There is a dc link round the camera cable involving the camera on-off switch. When working correctly the start up sequence is as follows:-
Mains on, main psu should settle at a bit less than 180 volts, camera psu fires up and the camera returns a signal to the main psu so that the voltage that reaches the camera is 180 volts. The point here is the main PSU should supply a lowish output until it gets the feedback signal to compensate for loss in the cable.
Check for dead silicon in the main PSU PCB and the SCR on the Heatsink.
The camera PSU is another kettle of fish entirely, again it is a inverter type. Most of the troubles are due to overheating of the main transistors. Check and replace the diodes in the base circuit. they MUST be fast types. 1N4448 more on this later.
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