LG 37LD490 - Glitching picture.

[tn245]

Re: LG 37LD490 - Glitching picture.

Reflow mainboard.

Are you guys doing reflows and counting on them as a lasting repair? What kind of methods are you using? I've got an LG which is failing when warm which I've narrowed down to main board. Tempted to reflow the processor with hot air station but much of what I've read points to reflow being only a temporary solution. What do you all think?

[jondoe]

Re: LG 37LD490 - Glitching picture.

Reflowing the CPU is a bare minimum kind of repair, you're hoping the solder balls reform well and the chip continues to function, until the same cause of the problem resurfaces, i.e. hot/cold stresses. Ideally, you want to re-ball the CPU with leaded solder balls which are less likely to fail over time.

I don't repair anything for commercial gain, just as a hobby really, so a long lasting, 100% repair job isn't something I'm too concerned about, I don't have customers, this particular TV cost me nothing.

I used a cheap Chinese rework station (998D), nothing special, but it's fine for tinkering purposes.

[tn245]

Re: LG 37LD490 - Glitching picture.

I'm usually selling on what I repair so would prefer to know that it's not going to die again a few weeks later. Interested to hear others experience with longevity of repair and reflow tips.

[jondoe]

Re: LG 37LD490 - Glitching picture.

If you want an idea of a more complete job, this video will show you;

https://www.youtube.com/watch?v=EZzQBcbaUms

I guess it depends on the length of warranty you apply to your work. I've re-flowed a Macbook GPU in the past, I gave it a 90 day warranty, with the money back if it failed in the same way. More than a year later, it's still going.

[jondoe]

Re: LG 37LD490 - Glitching picture.

After a great deal of testing, the picture and inputs continue to work. It does still have one problem.

I bought a replacement remote as the previous owners had long ago lost the original, claiming it never worked very well so they stopped using it. The replacement is very intermittent, as a test I used a universal remote and they too is intermittent, so the assumption is it's the TV.

For the hell of it, I've ordered a very very cheap spare IR sensor board to swap out, but while I'm waiting, does anyone know if this is a common fault? I read the voltage on the IR receiver, it's voltage would fluctuate when receiving a signal, so I'm hoping it's not still a problem with the main board.

[dick_barton]

Re: LG 37LD490 - Glitching picture.

If you have access to an oscilloscope you should be able to monitor the IR pulses being received by the set.
Also worth checking the voltage on the IR board is within spec.

[jondoe]

Re: LG 37LD490 - Glitching picture.

Unfortunately, I don't have a scope, I haven't graduated to that level of tinkering yet

I could see from the voltage fluctuation on one leg of the sensor it was registering the constant signal from the remote, when you let go of the button it would settle to a stable voltage, although I have no idea what the voltage for the IR board is meant to be as I never could find a service manual for this TV.

[vinceroger69]

Re: LG 37LD490 - Glitching picture.

what voltage do you have going to the ir board when the sets working maybe then check it again when the sets playing up that should rule out a supply voltage problem to the ir board

[jondoe]

Re: LG 37LD490 - Glitching picture.

On the IR sensor itself there is 1.58v and 3.0v on two of the three legs, the 1.58v leg varies depending on signal.

There are a few voltages coming into the IR board over the 12 pin connector, 3.3v being the highest I noted.

[vinceroger69]

Re: LG 37LD490 - Glitching picture.

next time it plays up be nice to see if the supply voltage does drop at all probs the 3.3v one.
Im not sure if a fault on the mainboard could cause this issue/fault i wonder if its also worth doing a factory reset and see if that helps with the issue at all.

[jondoe]

Re: LG 37LD490 - Glitching picture.

It's one of those annoying faults where for 70% of the time use the remote fine, but then some times it takes 3 or 4 stabs at the button for something to happen. This tends to be the same from cold start or while toasty and warmed up. I can't seem to find a pattern to it. I have tried a factory reset, when I tested the Ethernet it also updated itself to a newer firmware version, still the same.

Although I can't find the exact service manual I've found one for the TV with the same chassis. In that I can see the main chip LGE3556C doesn't have any obvious references to IR, although I think the following;

IR_INT : GPIO_23
IR1_IN : GPIO_25
IR2_IN : GPIO_29
IR_OUT : GPIO_26

could be it? I'm really not sure. It's possible I've just been unlucky and all but the remote was "fixed" during the reflow.

[vinceroger69]

Re: LG 37LD490 - Glitching picture.

its a pity are replacement main boards cheap and available for this set? whats the mainboard number/s used in this tv.

[jondoe]

Re: LG 37LD490 - Glitching picture.

EAX61531909 (2) is the board number, they seem to be a little thin on the ground, probably because people can't be bothered with a reflow/reball.

It's possible the 2nd hand IR board will fix the issue, but it might confirm the main board is duff, it's 50/50

[vinceroger69]

Re: LG 37LD490 - Glitching picture.

have you done a reflow on all solder joints on the ir board also where the ir board joins the mainboard

[jondoe]

Re: LG 37LD490 - Glitching picture.

I've tested continuity on the sockets and the cable, they seem OK but I guess I could give them a little attention with the iron, wouldn't hurt!

Attached is a picture of the IR board, it's pretty simple looking, I've tested the zeners, caps and the resistors, they seem ok, although I've not tested the two transistors.

[vinceroger69]

Re: LG 37LD490 - Glitching picture.

as you say if the old owners complained it had issues to it has to be the ir board or mainboard does this set have side buttons do they all work ok? if so i guess you can use them but if your like me you like a 100% fix no faults etc.

[jondoe]

Re: LG 37LD490 - Glitching picture.

The side buttons work fine 100% of the time, they plug into this board, so some of it is working. I assume that the button signals go back to the same place, so maybe it's the IR side of the board thats iffy. They said they'd used it with the side buttons for a long time and just used the Sky remote to change channels. It was when the HDMI's stopped working and the picture was tearing they gave up on it completely and gave it away.

I do prefer a 100% fix, the panel in this TV is pretty decent in terms of picture quality, so it would be a shame to ditch it when I'm so close to the finish line.

[jondoe]

Re: LG 37LD490 - Glitching picture.

OK, swapped out the suspect one for the 2nd hand one and its even worse. Other than allowing the TV to come out of standby once, none of the remote control buttons function at all. Swapping the original board back in allows gives me back most functionality...

I've given it a stern look, but it refuses to cooperate.

[vinceroger69]

Re: LG 37LD490 - Glitching picture.

i would send your new board back and get a refund i wonder if somehow this board needs to match the mainboard? seems odd it just turns it on

[jondoe]

Re: LG 37LD490 - Glitching picture.

I've attached a picture, they could be twins! It's very odd, I tried them both in and out a few times, no change in function.

The mind boggles!