Thursday, April 19, 2012

Electronics query by Mr. Patrick, Electronic repairer from South Africa

Hello Mr. Humphrey, thanks for the e-book I did receive it and I didn't have much time to let u know that the very 1st day u sent it I did receive it. It’s a great read & I’m so happy that now I can tackle any TV set. 

There is one strange thing though I wanted to ask you although I haven’t read much about vertical ic, I was fixing this Chinese made TV with single horizontal line be4 I bought your book so I did changed the vertical i.c LA78040 with a new one & replaced all the filter capacitors to this i.c rated 1000uF 35v and I did check the vcc pin 2 & 6 were getting 24 & 23 volts respectively.

I checked underneath the circuit board for any dry joints using magnifying glass & there was nothing but I still got the single horizontal line, then with sheer luck I had another TV (Sanyo model) with the same matching pins of CRT neck board of that Chinese swapped it together and there was no single line but the screen had raster lines at least the screen was full though not visible I think requiring some tuning.

My question is: is this how this Chinese screen dies or there is something I missed? Thanks

Hi Patrick,
From what you have said I pick that you changed the whole tube, I mean you took the motherboard of the china TV and fixed it into the Sanyo tube…if this is what you did then the only thing /component that added value for the vertical circuit in the swap was only the vertical yoke and I believe this was the only component which was suspect…

So I suggest you test the vertical yoke with a fly back tester or check if its open with analogue meter or even loose connection at the CRT neck( I have seen one of the wires to the CRT neck loose/just hanging or dry joints at that place.

For now I don’t suspect a bad tube…Bad tube has nothing to do with the horizontal line across the screen…this is the work of the vertical circuit.

Regards Humphrey

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