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LG 42PC1D Clicking repeatedly

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tom66:
I have a LG 42PC1D to repair. It is clicking repeatedly.

I thought I would have an easy fix when I noticed that 6 of the 3300u/10V caps had gone bad and one 680u/50V had too, all of them bulging. So I replaced them but still no joy, it continues clicking. ESR test on them showed they had gone to about 1 ohm each apart from one which was still in spec (the 680u measured 0.02 ohms.)

It has similar symptoms to bad capacitors. It will click once every 5 seconds (inrush relay) but sometimes clicks two or three times in a second. I have left it for 20 minutes and heated it up with a hairdryer with no luck to get it to start up. Every so often when it clicks the screen flickers, this tells me the Y-sus is most likely okay. When either Y-sus or Z-sus are disconnected it still clicks and the fuses test okay on those boards.

There are three Samyoung 3300u/10V caps which I didn't replace, I will shortly replace them and will post back here if that fixes the problem. There is also a Samyoung 680u/63V which could be bad so I'll pull that and test it for ESR.

Any hints/tips would be much appreciated.

tom66:
I replaced all the 3300u except one I could not reach but ESR was still good. I also removed a 1000u 10V and found it to be failed even though it wasn't bulging... Even after replacing all of these, it's still not working. Any ideas?

cdel:
hi,

did you check all voltages?

i have main and audio video board.

tom66:

--- Quote from: cdel on January 03, 2012,17:48:21 ---hi,

did you check all voltages?

i have main and audio video board.

--- End quote ---

I think most of the voltages are there. I will check later with a scope.

tom66:
Checked the voltages with scope. Very strange: the 5V rail is 4.92V which is fine, but the ripple is about 500mVp-p when the screen lights up. This looks a lot like a bad cap, but I've changed almost all of them. The only one left is a 680u/35V and a lone Samyoung 3300u/10V (but that's in parallel with 4x3300u Chemicon KY.)

Perhaps Chemicon KY is not good enough?

The Y-sus and Z-sus drive signals are all there and look good.

Vs/Va is good.

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