Sony TV 1902 GE..NO PICTURE NO SOUND only screen display ie channel Number.

Sony TV 1902 GE..NO PICTURE NO SOUND only screen display ie channel Number.

This is quite old machine over 10 years. The customer complains was that the machine has intermittent picture on and off. Usually if the picture misses they would tap slightly at the back of the TV at the RF inputs. Also the TV used to have a drift on the channel when off (every time they put off the TV they must tune again because they find the channel is not clear).

First suspect – dry joint. I did a thorough check for dry joint and I did all that I could but to no avail. Next is voltage checking around the CRT circuit and I noticed that the RGB collector voltage is high..ie 200 Volts before and after the 15 k resistor. All the three cathode. I measured the RGB BIAS VOLTAGE and I found 0.76 Volts in all three. Hence the reason why the collector voltage was not dropping. ie its like the RGB TRANSISTOR ARE OPEN BECAUSE THERE IS NO BIAS VOLTAGE.

I followed that circuit up the main ic processor and the voltage was the same.. I suspected the ic could be faulty…but before I embark on that mission I was to be very sure it is that ic because it is quite expensive to change.

By the way all other low signal voltage were ok..the 9 v, 12 volts were ok meaning the ic and the turner is getting powered.

I did esr test around the processor ic and changed whatever capacitor I was not happy with but still no change.

Then when fixing the Ariel into its sockets I noticed that it has some effect like if there is some disconnection inside the turner.

I opened the turner and did a thorough re-soldering. Both the inside of the turner and the inside of agc, if, sif, circuit(like the turner) and when I powered the machine. Everything is now perfect.

Conclusion.

I don’t know why this particular TV could cut the RGB bias voltage from the processor ic when there is not input from the turner. Usually in new machine the bias voltage I guess should be ok 3v each but the screen would be snow…no sound and picture though.

Anyway I learnt the hard way that whenever you experience no picture and no sound symptoms the best place to start is the turner circuits(inside and out the turner)…especially dry joints inside the turner and the VCC for the turner( 5 volts-turner, 0 to 33 v- turning voltage and 12 volts-band switching in some model)

The tuner components are usually quite reliable unless the antenna experiences a lightning strike. However, it seems that even after 40+ years of solid state TVs, manufacturers still cannot reliably solder the tuner connectors and shields so that bad solder connections in these areas are common even in new sets.

Also whenever you have a issue with any electronics gadget please take your time to think logically using flow chart to narrow down the problem to the actual circuit…very important even before you open the machine.

That’s all for today

Thank you and stay safe