TV TURNS ON, AND GOES OFF, AS SOON AS IT IS SWITCHED ON
This is a common fault to most of the CRT based [picture tube based] televisions. As we switch the set ON, by its power ON/OFF switch, the standby LED light once and the set turns fully Off state.
In
most modern televisions, the main system control IC is so programmed
that, as soon as it detects a short circuit in the main board, the IC
will detect the situation, and sill send a stop signal to main power
regulator section to switch the entire system OFF. This is a protection process.
The main cause for this fault is with the horizontal output section of the set. To make it sure, just disconnect the B+ power supply rail [usually come between 90 to 130VDC]. Connect a filament type bulb in series with this line to ground. Use a 100W bulb. Switch on the TV at this condition. If the bulb shows a glow, and stays lit, measure the voltage between the main B+ to earth. If
it is almost OK, make sure that the horizontal output section has the
fault. If the bulb does not glow at all, make sure that the fault is
with the missing B+DC line. Check for it.
If
the bulb glows constantly, and when you connect the B+ line, the power
supply switches OFF after a moment, concentrate on horizontal output
section. There are three components to be suspected. The first one is it
LOT [Line Output Transformer], the second one is line output
transistor, and the third one is a deflection yoke. Among
these, fault to deflection yoke is very rare, almost 1%, we can say.
Fault with the horizontal output transistor and LOT are common.
Desolder out the horizontal output transistor from circuit. Switch ON the TV. If standby light stays lit, and B+ voltage is OK. Make sure that the horizontal output transistor is leaky. Leaky means, it will have its internal junction [Collector to Emitter or collector to Base], has shorted.
There are tow reasons for this transistor to get shorted. The first one is of overheat. The second one is with some shorted extra high tension windings inside the LOT.
