LG 42PC1D Clicking repeatedly

[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]

hi,

did you check all voltages?

i have main and audio video board.

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.

[cdel]

 

if the all voltage are ok wild guest problem on eprom or main board.

[tom66]

if the all voltage are ok wild guest problem on eprom or main board.

Yeah, need to consider that.

Any easy way to eliminate the power supply?

Just checked the 680u for ESR and it measures 0.03 ohms so I put it back in circuit.

Also checked diodes and FETs - all okay.

Right now I am very confused by this power supply, and don't quite know what to make of it.

I have the service manual for the TV, but no schematic for the power supply. If anyone has one, that would be much appreciated.

[cdel]

i have main board if you wanna try give  me a big shout.

[tom66]

i have main board if you wanna try give  me a big shout.

How much?

[cdel]

£30 for audio video and mainboard including post.

[tom66]

£30 for audio video and mainboard including post.

You have me interested, sending a PM.

[tom66]

I found a 1.8V regulator on the main board that was putting out only 1.3V. However, I'm looking carefully at the datasheet (SC156515M) and it may be simply that it is automatically switching over (if ADJ > 0.2V, it uses that voltage; otherwise, it uses internal feedback resistors.) Will have a look later at the divider resistors, if any, to determine if it is faulty or not. Seems to power a main processor of some kind.

The package looks extremely difficult to remove as it's got a nice large thermal pad; so I may just replace the entire board if I find one faulty.

Tried resetting eeprom to no luck.

[tom66]

Sadly, I changed the main board & AV board, but it's still not working.

I noticed that when the Y-sus or Z-sus connectors are unplugged the voltages do not rise... when they are plugged in they are correct. Don't know if this is significant.

Going to have one last look at it, before assembling it and selling it for spares. I have spent nearly £100 on this with no luck so far. You win some, you lose some...

If anyone is interested, let me know. Comes with a recapped power supply and two new boards.

[tom66]

It's FINALLY fixed. It was the AC detect, something with it was wrong. No matter, I just bridged both optocouplers (the two on the board where the dot faces the other way) and it's now working perfectly. Low level sparklies & image retention, but nothing a bit of tweaking can't fix.

[cdel]

congaratulation.