they don't require isolation transformers. the whole left side of the chassis is the power supply unit (under the cage, if yours still has the cage on it). I personally encourage using an iso though, if you have access to one.
a wide variety of things could be affecting yours. is it making a slight ticking sound when you have it turned on? that could be the result of a blown HOT or the flyback could be bad (inspect for cracks just for fun). the B+ could be out of tolerance cause it needs to be capped. these are actually kind of complicated to work on.
if you have monitor repair experience, you _might_ be able to fix it. otherwise, I would encourage sending it off to Chad at arcadecrt for repair, he'll at least be able to sort out that nightmare on the neckboard for you lol
I had a chassis that still had high voltage, but no heater glow. after messing with that for a couple days I finally noticed that underneath the flyback, the chassis had cracks in it and there were several broken traces. I would additionally inspect the white block resistors outside the heatsink that goes around the flyback. the solder joints on those typically lift up or outright break from the heat put off those resistors, so ensure you have continuity between the resistors and the next points in the circuits.