On Wed, 22 Oct 2008 08:22:07 -0600, (Ken G.) put
finger to keyboard and composed:

I have an old asteroids full size vintage video game .
I has a black & white monitor .

When it first comes on its fine . Within 10 minutes the whole image gets
bigger , things disappear off the edges . The center of the screen gets
a bit darker .
I suspected the hi voltage diode off the flyback and adjusting the hi
voltage pot but replacing that did not help .

I dont have any model #s the monitor has one medum circuit board and
one small board with the flyback in a metal box .

Thanks

The "blooming" does sound to me like a low EHT problem. I'd check the
B+ going to the FBT, and the base drive to the LOP transistor. Make
sure the duty cycle doesn't change. I've seen this happen in an old
IBM monitor as a ceramic capacitor in the horizontal oscillator warmed
up. However, in my case the EHT gradually increased until the HV
protection shut down the monitor.

- Franc Zabkar
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