Monday, January 27, 2020

14-inch China made CRT television screen colored with a black slip at the bottom of the screen now repaired:

I received this television from a customer who wanted it checked and the screen had spots and the bottom of the screen had a blank slip across the screen which made the height narrow.

Usually if there is something on the screen it can help the technician locate where the problem is even without opening the set.

In the case at hand since the screen height is affected we can conclude that the vertical circuit has a problem.

Therefore, after opening the set I will proceed straight to the vertical circuit.

This television was using the popular ic LA78040 which is attached to the heatsink using a bolt as you can see below.

I scanned the vertical circuit with my naked eyes with the main suspect in mind being capacitor, especially those with top part swollen and I was not lucky.

I pulled my ESR meter and I bumped on 3 capacitors which ESR was too high to any electronics device on the surface of the earth.

The capacitors were C450(100uf/16V), C451(100uF/35v) and C456(4.7 uF/50V as you can see them below.

Looking with your naked eyes you will see they all look very innocent until you use the esr meter will know that things on the ground are different as you can here below.

The 1000 uF above is now reading a capacitance of 26pF, the ESR reading is beyond my meter range.

Capacitor 456 rated 4.7Uf/50V above is now reading 0.15K ohm, this is again abnormally high.

After replacing the three capacitors now it is time to test and after applying the power his is what I saw.

The television is now back to normal and even the colored spots are gone.

Thank you

Stay safe

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