check your rectifier bridge and see if you have an open diode. also open F901 and just measure the voltage there, that way you aren't running the chassis.
you should have over 130vdc ish (depending on your actual line voltage level.) if it's 60 ish there, you have an issue in your line input and/or bridge rectifier
check the B+ pot, sometimes they get crud in them. note it's position then spin it back and forth a few times and get the crunchys out.