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I think it needs to be replaced. If it were a pre-war TV, or even a 15" color set, maybe I'd try to fix the FBT. But in this case, they're available with some patience and searching. My experience is that it DOES speed up the ruin of the FBT if the TV is operated on a higher line voltage (such as by setting the "LO-NORM" line switch to "LO" when it's been in "NORM" all the set's life. Also, a fast way to destroy an RCA flyback is to set the HV adjustment any higher than it was. I leave it alone, even if the HV is measuring low.
When a new FBT is found and installed, I'd suggest checking the horizontal oscillator circuit in case it's stopped or running at a weird pulse (scope it at the plate pin of the Horizontal Oscillator tube with the horizontal output plate cap removed). A problem with the horizontal oscillator will heavy-load the output tube and burn up the FBT. If you want to do a quickie check, get a plain old neon tester and hold it next to the cap (neon tube itself; not the leads), near the cap of the H. Output tube while the set is warming up (cap installed on the H. Output). If the oscillator is working, the neon should glow as soon as the tubes warm up, and comfortably before any damage would happen to the FBT. If it doesn't light, your oscillator isn't running, or there's something loading down the horizontal output.
Charles
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Collecting & restoring TVs in Los Angeles since age 10
Last edited by kx250rider; 04-15-2009 at 10:10 AM.
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