CTC197 typical FBT symptom but FB rings ok

RCA F35676MB, CTC197CD, ser 649560677, mfr Dec 1996.

Have you had one of the CTC197 FBT failures where a ring test shows good but the flyback is shorting or arcing internally only under full power?

This set has the "four strikes you're out" symptoms of a bad FBT reported in this group in the past.

Power supply seems okay - in standby have 144 V, plus the lower voltages and regulation appears good. When the power is turned on, the 144 drops to about 100 V each time the set trys to fire up, then returns to 144 or so back at standby.

In previous postings this symptom has been diagnosed as a faulty flyback and most reported that changing the transformer fixed the problem. However, this flyback rings good, and the yoke winding also show no apparent fault. The HOT is okay.

I'm wondering if the CTC197 problems with the FBTs that were repaired by replacement in the past were confirmed with a ring tester, or if the failures showed up only when the HV comes up, as it might be in this case.

Michael (C.E.T.)

Thanks AJ

My experiences with bad LOPTs has been that they either showed at least some visible signs (cracks, bulging, discoloration, dark carbon traces, pin-point arcing to core etc) and/or they fail the ring test. But I'm not discounting the possibility that in this one there could be an internal breakdown only at HV.

When the set came in, I cautioned the owner that it could be the FBT and the instruction was "if so, don't bother repairing". I'm trying to avoid having to bring in a replacement transformer to prove the point as I won't recover the cost of the part in this round. At the same time, I want to be reasonably certain that the diagnosis is correct.

Knowing that this has been the experience of others (failed LOPT but no visible sign s and passes ring test) is reassuring.

Michael (C.E.T.)

LOPT

time