NotTaR of Television Sets : High voltage shutdown due to X-ray prote..  
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High voltage shutdown due to X-ray protection circuits

A TV that runs for a while or starts to come on but then shuts down may have a problem with the X-ray protection circuitry correctly or incorrectly determining that the high voltage (HV) is too great (risking excessive X-ray emission) and shutting everything down.

A side effect of activation of this circuitry is that resetting may require pulling the plug or turning off the real (hard) power switch.

Was there anything else unusual about the picture lately that would indicate an actual problem with the HV? If this is the case, then there may be some problem with the HV regulation. If not, the shutdown circuit may be overly sensitive or one of its components may be defective - a bad connection of leaky cap (or zener).

If the horizontal frequency is not correct (probably low) due to a faulty horizontal oscillator or sync circuit or bad horizontal hold control (should one exist!), HV may increase and trigger shutdown. Of course, the picture won't be worth much either!

One symptom of excessive HV (but not required) is an overly bright picture of reduced size.

The HV shutdown circuit usually monitors a winding off of the flyback for voltage exceeding some reference and then sets a flip flop shutting the horizontal drive off.

On some Sony models, a HV resistive divider performs this function and these do fail - quite often. The big red Hstat block is a common cause of immediate or delayed shutdown on certain Sony monitors and TVs. See the section: Sony TVs/monitors and Hstat.