Old 465: Dot appears when flipping on the power, immediately disappears.

[Eisen Feuer]

Hi everyone! I have a scope that was working flawlessly on both A/B channels (I was using X/Y mode with both channels to visualize audio) until after a while, the scribe started to disappear from the screen. Fiddling with some controls and power cycling would bring it back, but the only time I can get anything displaying now is the first quarter of a second after pulling the power switch on, I get a quick quarter-to half inch left-right squiggle of bright light a little bit above screen center which appears sometimes to be scanning toward center. The dot's brightness is relatively constant if you're not starting it cold, and doesn't seem to obey adjustments to the Intensity knob.

I wasn't performing any strange or high energy tasks on it when it was going bad, just feeding it line level stereo audio (10V or less?) out of a phone. I did have it vertically oriented though (screen looking at the sky), if that matters.

I tried:
Beam finder does nothing.
Scanning around every position imaginable with the position knobs.
"percussive maintenance"
lots and lots of switch flipping


I'm here crossing my fingers there's some enthusiasts out there to tell me this is a dime a dozen problem they've seen a thousand times
I'm technically inclined but if things descend into looking at schematics in the manual you might lose me.

Thanks to anyone who replies! I don't at all mind putting a $20 Paypal bounty for the first comment that leads to a fix!