LG CRT Television mode RT-21FB55VE picture top squashed.

I received this television in my shop with the complain of having the top part of the screen squashed and the part of the picture with dark stripes.

I applied the power to confirm what the customer said and this is what is saw.

Usually when troubleshooting television problem which is able to power up one can easily narrow down the faulty circuit just by watching the screen.

In the case at hand I could see there is a problem with the vertical height of this television and whenever you see the screen is not full upwards or it full but with dark stripes this point to the vertical circuit not doing its work well.

With that initial observation I decided to open the set and headed directly to the vertical circuit.

Because there was something on the screen I was sure the vertical i.c was still alive but working under poor working condition.

For ics to work well they require good supply and without any ripple. So any supply which is not clean will cause i.c. to have a lot of stress.

All ics used DC current and therefore to get clean Dc, capacitors are used to make sure ics are feed with clean DC.

The moment the capacitor fail to do his work well this will usually affect the smooth running of ics which eventually fail completely.

Most technician when they find a television with a single horizontal line rush to change the vertical ic and think that they have solved the solved only for the customer to come back again after a few days with the same problem

This is because the technician solved the symptom but not the cause.

The rule of the thumb is that hardly does an ic die alone, there must be a cause and most of the cases the problem is the capacitor.

So I opened the set and headed straight to the vertical as show above.

I scanned the top of the four capacitors within the vicinity of the vertical circuit and all of them looked okay according to my eyes and no sigh whatsever to make me suspect they are not innocent.

So I decided to pull out my esr meter and do esr testing on the capacitors around that circuit.

 

Because they were very few capacitors around that circuit I only took less than 2 minutes to check the capacitors and I was not happy with the capacitor C415.

To be sure that this is the culprit I decided to download the circuit diagram of this model which was readily available online and looking at the location of this capacitor I could see that it is indeed used to filter the vertical circuit supply as you can see circuit diagram below and therefore I was sure that this was the one causing the problem.

As you can see this capacitor is filtering the positive supply of the vertical ic(+14v)

I replaced the capacitor and after applying power I was happy to see the screen was now full vertically speaking as you can see here below.

Thanks guys, see you in the next class

Humphrey Kimathi