What could cause a handful of dead phosphors seemingly overnight? RCA MM36110

[old_tv_nut]

Originally Posted by RCATUBES

...
Sometimes on startup there is a brief vertical flash in the center of the screen, but it's an inch or two ABOVE these burnt-out phosphors so I doubt that caused it...

I'm guessing that one time your vertical flash wasn't very tall and fell on this spot, burning it, but I have to say I've never seen a color CRT burn like this.

Has anyone else seen a color set get a burn from deflection failure? Does this set maybe have a spot killer circuit that's not working?

[vol.2]

Originally Posted by old_tv_nut

Does this set maybe have a spot killer circuit that's not working?

That was my thought. I remember watching a YT video about center burn-in being caused by a bad cap that eases the shut off process when the beam collapses, or something like that anyway.

In any case, the burned spot in the center of the screen basically looked like that.

[RCATUBES]

Originally Posted by old_tv_nut

I'm guessing that one time your vertical flash wasn't very tall and fell on this spot, burning it, but I have to say I've never seen a color CRT burn like this.

Has anyone else seen a color set get a burn from deflection failure? Does this set maybe have a spot killer circuit that's not working?

Yeah, I've posted this question in a few places and screwed up spot killer circuit seems to be the leading theory. I'll have to dive into the service manual tonight and read up on that.

At this point I've basically written off the tube as a loss. Since the black spot is dead center, it's going to be very distracting any time there's a solid color in the middle. And its extremely distracting on 31.5khz inputs where there's not big thick scanlines to help hide part of it. But I'd still like to get the chassis working properly to prevent further damage, and also because I've started searching for anyone who might have a dead MM36100/36110 with a good tube that I could use for a replacement.