Quoted from Arvid:
Thanks for the reply. It is this one, directly connected to the PCB? Or is it located elsewhere in the cab?
That's the neck-board of the CRT... that isn't where main power is disconnected from the monitor... you need not mess with that.
There should be a rectangular 3 pin connector... with three wires, white, black and green. Similar to what you see in this picture. Probably on the right side looking into the rear of the cabinet. The one you see in this picture is the power to the computer... but that's what your looking for.
Be careful messing around with that monitor.... especially if it has been powered up recently. The tube (where the HV cable connects to the cup) can hold a charge. If you are going to remove it, you need to disconnect the main power (what you are looking for) and the video cable that connects the monitor chassis to the computer (unplug it from the computer... leave it connected to the monitor for now)... AND the lamp tube power as it is attached to the monitor frame (it uses the same type connector). Once all the cables are disconnected, remove the 4 bolts and lift it out carefully.
Disclaimer on my instructions: I'm assuming it is 100% factory and hasn't been hacked or re-wired. People tend to make a mess of these things when they work on them or do any sort of conversion.