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(In a "past life", before throwaway TV's, I was a TV repairman, certified by a couple of brands.) There is a circuit that senses the (approx. 30KV) voltage aplied to the picture tube anode, using a voltage divider to feed a reduced voltage (pulses) to the monitoring circuit. If the HV IS exceeding design limits, the circuit "kills" the HORIZ oscillator circuit, effectively shutting down the TV 'till it's shut off, and the circuit rests. ("X" rays can be produced if the CRT's andode voltage exceeds safe limits.) So, the first scenario is that the safety shutdown circuit is behaving properly, and there's a power supply regulation problem. Too much B+ voltage (typically runs around 130 volts), and there will be too much HV, and the safety circuit will kick in, shutting the set down. The other scenario is that the safety shutdown circuit itself has gotten a bit of a "hair trigger" attitude with age, and is needlessly shutting down the set. EITHER scenario is commonly caused by an electrolytic capacitor that has either become "open" or "leaky". (OBVIOUSLY, there can be MANY different causes for this behavior BESIDES one or more 'lytics.) Figuring out WHICH of the dozens of 'lytics that MAY be going bad requires a service manual (at the very least, a schematic), and some knowledge of working on the innard of a TV without getting zapped by the 120 VAC "live chassis" parts, the B+ power supply section, and the HV section. Oh, yeah, and an "isolation transformer". DON'T mess around in there, unless you have the safety knowledge, a service manual, and an isolation tranformer.
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