Aha! Okay, this is probably cool. Here's what I would do:
1) remove the harness from the board, just in case.
2) remove the AC power going in to the power supply.
3) Remove power from the marquee fixture.
4) Replace the FAST BLOW main cabinet fuse and replace it with a slo-blo, 5A. If you don't have one, just use a nail. Normally I wouldn't suggest this, but because the monitor is already fused, this should be okay.
At this point the only powered thing in this cabinet SHOULD be your isolation transformer.
5) use the lightbulb fuse on the monitor, or replace the fuse. If you use the lightbulb, and it comes on bright, just wait a second, it'll probably go dim and the monitor will fire up.
Here's my guess: the fast blow fuse is being stressed way past its blowing point almost immediately. 3A is pretty low, and that sudden draw could certainly kill it right away. At the very minimum it should be a 3A slo-blo so it has recovery time.
With nothing else hooked up, the only point of failure at this point is the monitor. If you use the lightbulb fuse it might take a second to come on as the caps charge. Of course, kill the power right away if anything starts to smoke.
