The
TV got for repair in Dead condition.
When I powered it, there was no power indicator; and a ‘keee”, ‘keee’
noise heard from the circuit board inside.
A clear indication of short circuited component/s at its main
board. My service experience lead me to
de-solder out the horizontal output transistor, and power it up. I did so, now the power light is there, first it
show green in colour and then after 3 seconds it turns to red colour.
Checked
the horizontal output transistor (TT2140).
Dead short (Collector to Emitter). 
There
might have other reasons too. Without
checking for it, if I replace this transistor, the new one too will get
shorted. So I checked further.
Checked
the frequency of oscillation that comes to the base of the horizontal output
transistor. Found abnormal. Instead of 15625Hz, it shows
45750Hz. This might be the reason for
the failure of the horizontal output transistor. Checked all the pin voltages of the main
system control chroma jungle IC.
Voltages at some pins shows abnormal.
Checked all the solder terminals of this IC. All look fine. Re-soldered all the solder terminals to confirm that there is no dry solder to any of it.
Powered
the set ON. Checked the frequency
again. No change. Show the same as
before. 45750Hz.
Replaced
the oscillator crystal with an exact replacement. Now too, it shows 45750Hz.
Damage
to the main system control chorma IC (TDA8370PS/N3) confirmed. Its step down counter section circuit inside should have some fault. Replaced it.
Checked the frequency again.
Shows correct. 15625Hz.
The
reason for the failure of the horizontal output transistor too is
confirmed. High frequency oscillation
signals from the system chroma IC.
Replaced the horizontal output transistor (TT2140).
Powered the set ON. Ok.
Checked
the set for 2 Hours. No other
problem detected.
