REPAIR of 21 inch TV with a single horizontal line

jefflumiri (34)in #life • 7 years ago

The TV belong to my friend; he talked to me several months ago about his TV which was having some white lines across the top part of the screen. I told him the TV needed urgent repair but he ignored, I forgot about it until he came to me one morning for the same problem, this time, the problem had worsened. The problem had changed the TV had a single line across the screen. I i took my usual mini kit, small digital meter and a screw driver. I opened the set and went straight to the vertical circuit.

I did some scanning around the components there but got no physical sign of stressed component. So I took the board with me to my work shop for further testing, on my workbench I pulled my ESR meter because I was suspecting a faulty capacitor. This is because his first complaint was white lines across the top of the screen which is usually caused by capacitor failure. Within two minute I was able to pick capacitor C451 (100uF/35V) which had its ESR gone to the roof.

A normal capacitor of this value should have an ESR reading of less than 1 ohm on ESR meter but it was now reading 34 ohms. As you can see the capacitor looks very innocent and that is why I always request new technicians to invest on an ESR meter. I salvaged another capacitor from a junk board and installed it.

After getting this capacitor I was very happy and I didn’t continue trouble shooting, the following day I was back to his place with the board, after installing the board and powering up with my eyes fixed on the screen I was a disappointed man..No change.

Very fast I concluded that since this capacitor is very critical to this I.C then most probably its faulty lead to the destruction of the vertical I.C.

So I replaced this I.C and I was now very sure that I had solved that problem once and for all. I applied power to the TV and again looking at the screen still the problem was not solved. This is when I decided to get more serious with this repair and to start with I decided to go to that circuit (vertical) and solder out one leg of each component and test them one by one. I started with resistors and I got a resistor which read open to my meter but looking at the colour marking did not make sense to me. The resistor had a reference R461A

I tried to look for a circuit diagram which is close to this TV model and I bumped on this China TV circuit diagram.

To my surprise this resistor actually act as fuse for the vertical circuit and once it opened means the supply to the vertical circuit was cut off hence the horizontal line on the screen. This also made me to conclude that the I.C could have actually shorted and that is what caused this fusible resistor to open.
After replacing that resistor I went back to the owner and reinstalled the board still not sure if I got everything right this time and after applying the power this is what I saw.

Lesson learnt is that it is not good practice to take any repair assignment as yet another easy task. I believe if I did voltage testing around that circuit I could have picked this resistor on my first attempt. Anyway I learnt my lesson and the customer was happy to see his TV come back to life.