Screeching, assuming it comes from the monitor, sounds like it's either operating at a too low horizontal frequency or cycling on/off for some reason.
Have you checked the regulator Q801 after the HOT blew? If it is shorted the power supply voltage will be too high and it should shut down or possibly cycle on/off (which might sound like a screech).
Could there be some bad component or solder joint around the control IC?
Or maybe open circuit? A bad connection or bad component related to the horizontal deflection yoke could also mess things up.
What is it powered from? Mains frequency isolation transformer or SMPS?
I helped a friend repair the monitor in a Defender cabinet where the HOT and power supply regulator transistor had blown. Actually it blew up while I was playing the game
After replacing the HOT I powered it up with a lab power supply feeding its regulated ~110V rail but observed abnormal consumption of almost 100W and a funky stretched-out waveform on the collector of the HOT. Quickly shut it down.
The problem in this case was a shorted film cap in the horizontal deflection circuit. Verified operation on a lab power supply after replacing the cap, now drawing about 30W. After replacing the power supply regulator, actually a hybrid in this unit, it worked fine.
Bad guy:
Testing waveforms:
Diff probes to measure HOT Vce and Vbe (Vce is about 1 kV pk so a normal scope probe won't usually stand this).
Works again