There is a malfunction in the THT

Hi Hashim.
EHT (Extra High Tension) usually reefers to the 24kv to 30kv, focus and first anode (A1) voltages required to operate the crt (picture tube). These voltages are supplied by the line output stage, primarily the line output transformer (often refered to as the flyback transformer). This transformer steps the voltage up to 8kv and an embedded rectifier trippler circuit tripples this to 24kv dc to supply the final anode voltage to the tube (Hence the big rubber cap and thick cable.
The line output transformer is driven by a smaller transformer (line driver transformer) via the line output transistor.
The driver stage is fed by the hoizontal oscillator circuit.
So we can see that a failure in any part of this circuitry will most often result in no picture. The line output transformer is the heart of the system, it not only supplies the EHT voltage it also has to
supply an LT voltage for the vertical output stage but also the sound output stage.
A Fault in the A1 circuitry would result in a very dark picture but sound ok. Or the picture badly out of focus.
The line output transistor going short circuit results in no picture and no sound with the set shutting down to the standby mode or
hic upping (making a ticking noise. This problem would be amongst the most common and is easily confirmed with an Ohm meter. The line output transformer itself can develope an internal short with the same results (less common). Failure of the line oscillator and driver stages are most easily confirmed with an
oscilloscope. A fault in the power supply will also give these symptoms. To confirm line output stage is functional look to see if the tube heaters are glowing, this supply also comes from the line output transformer. Can you feel the static if you run the back of your hand across the front of the screen (often feels like running your hand through cobwebs. this would indicate that the EHT is present and the fault is elsewhere. Understanding how something
works enables you to find out why it doesn't. If you have occasion to replace a short circuit transistor, be sure to reslder all pin connections to the line driver transformer. I've found dry joints here
to be a cause for random inttermittent failure of this transistor,
Best regards from Vintie.