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Old 07-31-2012, 09:42 AM   #1
Daigoro
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Default LG 42" LCD (42LH3000) T-Con/tab bond problem?

Hello all

While this is probably not a "bad caps" problem I thought I'd post here since there are many other threads on this topic.

Buoyed by my success with repairs to LCD monitors, I have been on the lookout for a faulty LCD TV to play with. Last week I was lucky enough (or so I thought) to acquire a 42" LG (42LH3000-ZA) with what I was told had been an intermittent fault which had becoming more frequent. I had hoped it would something nice and simple like dodgy power supply capacitors, sadly that does not appear to be the case.

The picture is mostly OK on power-up but after 30-seconds-or-so the brightness will fade, accompanied by a black horizontal line, and the picture displays a very slow motion blur - like a psychedelic video effect -evenly over the entire screen. The picture may also exhibit this problem immediately on power-up, with no delay.

Apart from the motion blur, the picture is quite clear. I have tried to capture the effect in the attached photographs.

I have fully disassembled it and checked all the connections. I have also carefully massaged all the tab bonds with the TV powered up but have been unable to identify any bad connections there. (The metal frame actually has some factory-fitted rubber blocks which press against the tape)

From what I've read, it sounds like a tab bonding or control board problem (or possibly main board) but since I haven't been able to resolve the problem by applying pressure to the tab bonds it seems unlikely - but not impossible - that's the problem.

My questions is: could a bad tab bond cause this problem across the entire display or is the control board (or even the main board) more likely?


Any advice gratefully recieved.

Thanks.
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Old 07-31-2012, 09:51 AM   #2
minimania
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

could be a bad lcd panel or tcon board
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Old 08-02-2012, 01:01 PM   #3
exsonyexpert
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

look at ur t-con board if have square i.c with this description as15 or as34
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Old 08-02-2012, 09:05 PM   #4
cadiman
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

faulty panel tab bond will give you the slow motion blur lagging motion etc.

If that is an au-optronics panel you are lucky it still has a backlight.
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Old 08-03-2012, 09:29 AM   #5
Daigoro
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

It is an AUO panel (T420HW04) and AUO control board - if I'd bought this TV I wouldn't feel in any way lucky! This television is only 2 years old and was used in an office video conference system, so it's not like it has had a hard life.

I don't see a chip with those identifications. There are two square ICs: the main one is AUO 12401, and a smaller one, RM5101.

Can't really bring myself to spend money on a replacement board when the panel's in doubt. I may give the control board a blast with a heat gun in case there's a bad connection. Might also do the same to the processor on the main board since it's a BGA - nothing to lose. I'm also tempted to replace the output caps (Samyoung) on the power board since that would be relatively cheap - the voltages seemed OK but maybe they're on the way out. Maybe.

Clutching at straws, I know!

Thanks for looking.
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Old 06-12-2013, 09:33 AM   #6
Daigoro
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

Just thought I should update this thread for the benefit of others.

Having held on to this television for the better part of a year - and even though I had investigated the tab bonds several times without identifying a problem - I decided to go ahead and add some foam pads under the tab bonds (the metal frame already had factory-fitted blocks)...and it worked!

Videos of this problem generally show the display problems resolving when the faulty bond is touched but this was not the case for me. It seems like the TV cannot recover from this fault without a power cycle. Indeed, it has failed again a few times since the repair and simply switching it off and on again has been enough to resolve it. So far.

Kicking myself for not trying it sooner.
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Old 07-08-2013, 05:17 AM   #7
Daigoro
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

Well, this worked for a couple of weeks but it has failed again. So I opened it up expecting to have better luck locating the fault - unfortunately that has not been the case. No matter what I do, I am unable to track down the problem. I have been over all of the tabs several times and found nothing to indicate that there's anything wrong with any of them. So I'm inclined to think, sadly, that it's probably the panel itself - unless anyone has any other suggestions?

Landfill....
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Old 07-08-2013, 06:15 AM   #8
newtothis
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

Well since applying the pabs temp solved the issue the problem must lie with the bonds.... that being said the tv is irrepairable unless the panel is replaced.

Shame but welcome to the world of gambling with tvs lol
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Old 07-25-2013, 06:43 AM   #9
Daigoro
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Default Re: LG 42" LCD (42LH3000) T-Con/tab bond problem?

One more piece of information which might mean something: There are two flat cables which run from the T-con board to another two boards which then feed the two halves of the panel; if I leave either of these two cables disconnected I get half the picture (obviously) but the fault persists regardless of which side is disconnected.

Is this indicative of anything useful, or are the tab bonds on the disconnected side still part of the circuit?


Thanks

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