Thursday, September 9, 2010

JVC Television Dead 21”

One day I was brought a dead JVC TV to repair; when I pressed the power ON button, I could hear the degaussing coil engage as usual on power on.





 I opened the set and I measured the voltage across the main capacitor. No voltage was found-absolutely zero volts. Alas what is the problem now? All over a sudden I heard a loud crack sound and noticed a resistor has broken down—see resistor R904 above across the degaussing coil- what was it doing there in the first place(anyway in most set its written optional but in this case it was there)

I never had a chance to know its actual value to date. It was also very hot and broke into pieces.

After that the voltage was able to flow up to the control chip (STR-F6653). Now pin 1 is 318V dc which is normal in this case but there is a funny reading on pin4( start up VCC pin) it should be 19 volts but on my meter it was reading less than 12volt and pulsating-usually when you find lower voltage than expected and pulsating means there is a shorts on that line.


So I lifted up the VCC pin 4 and the voltage increase to 25volts. With that I concluded that that I.C was shorted on that pin.

I replaced the I.C together with Posistor and the unknown resistor which burst into flames instantly on power on. The resistor value which I figured was low resistance almost caught fire.

So I decided to leave this resistor completely and only replaced the I.C and the Posistor and the TV started running on like new. To date I have not replaced the resistor and the customer has never come with any complain. Isn’t funny sometimes we remove components to make a machine to work again.

What was the use of the resistor in the first Place. Remember in all this the fuse never shorted. Could it be even the Posistor was good also? Because there is no way a Posistor can short and the fuse does not blow....

A word of Advice:


Never disable the x-ray protection circuit because this can cause serious x-ray radiation which can harm the user- Always think safety first in whatever you do.


4 comments:

  1. interresting weblog and information. Keep up the good work.

    ReplyDelete
  2. Oh thank you, and God bless you.

    Regards Humphrey

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  3. woww.. :) we both got d same xperience(lettin out d burnt resistor & powerin up)..But this will mess up in some cases..

    God Bless.

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  4. Sure Jim, we should not do it on the X-ray protection circuit.

    Have a nice day

    Humphrey

    ReplyDelete