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However, if you discover an inch layer of filth inside the TV, the HV could simply be shorting out - clean it first.
In most cases, these sorts of faults will put an excessive load on the horizontal output circuits so there may be excessive heating of the HOT or other components. You may hear an audible arcing or sizzling sound from internal shorts in the flyback or tripler. Either of these may bet hot, crack, bulge, or exhibit visible damage if left on with the fault present.
Most modern TVs do not regulate HV directly but rather set it via control of the low voltage power supply to the HOT (B+), by snubber capacitors across the HOT, and the turns ratio of the flyback. The HV is directly related to the B+ so if this is low, the HV will be low as well. Faulty snubber capacitors will generally do the opposite - increase the HV and the X-ray protection circuits may kick in. However, low HV is also a possibility. The only way the turns ratio of the flyback can change is from a short which will manifest its presence in other ways as well - excessive heating and load on the horizontal output circuits.
While a shorted second anode connection to the CRT is theoretically possible, this is quite unlikely (except, as noted, due to dirt).