Okay let’s do this.

I was thinking why it would go dim and lose its zoom clamp. The dim is because the electron gun isn’t doing its job. The zoom is because the horizontal and vertical coils aren’t doing their job.

What drives both of those? The Flyback transformer. 100% certain the flyback went out on it.

I’ve read that if a CRT fails it’s most likely to be the flyback regardless. Which makes sense because that transformer cranks the ~120 volts input to somewhere between 10 and 30 thousand volts. there’s a whole lot of really damn tiny wire in there that’s prone to burning out.

So, what to do about this…

Internet suggests adding more loops to the coil; impossible as any crt from the last 15 years is sealed.

Internet suggests doing some weird thing to revive the crt; sounds bs but here’s the link, see what you think: http://ezinearticles.com/?How-To-Restore-Picture-Tube-Without-using-a-crt-tester,-restorer-or-rejuvenator&id=548647

My suggestion is to replace the flyback; but that’ll be damn hard. You’d have to find an exact model AND get it off the board without ruining it or killing yourself. Flybacks have a circular pinout that’s ****ing hard to work with imo.

Then there’s also the inherent risk of playing inside a CRT to consider. The majority of the parts in there are extremely high voltage; the sort of stuff that’ll kill you instantly.

You could always pull the main red cable from the flyback off the CRT (ground off the CRT first, it’s a giant capacitor) and put it near a ground. Turning the thing on should show an arc about 1-3 cm long.

If it doesn’t arc then the flyback is confirmed dead.

If it does make a nice big arc, the electron gun or deflection coils are dead.