Check FR401 supply voltage for X401 @ collector vert trans and X402
between the two trans is r420 a 5.6 ohm,check for open traces off the vert-trans
As always solder the pots/controls,and with monitor off, clean or
turn the controls back and forth a few times to clean the contacts
then return to spot you started. bad connections and open pots
can cause a few different symptoms..
I just had a G07-904 Hear HV for a second then nothing..
it went into shutdown,killing the Horiz-Drive..
Open fuse.. B+ good, I o-scoped HOT collector
could see messed up waveform at power up.
replaced fly,up and going now..
I use a regular o-scope with a 100 times probe
to measure waveforms on Collector of HOT..
If you monitor the waveform on any HOT you can tell
if the FLy is shorting inside,also a flyback ring tester..
Just sharing my experience,with this repair.
Good Luck!