LG 55LS4500-UD: Not Staying On

[ECU_Techie]

Hi all,

Ok, so here we have a 55" LED tv by LG. According to the person I got the tv from, they said ever since lightning hit their house they would have an issue getting the tv to stay on. It would come on briefly, some times turning on to the point of the no channel or input detected screen and then the tv would shut itself off and sometimes not come back on.

Upon plugging the tv in myself, they are correct. I got it to turn on enough to display no channel and it turned off and I can't get it to turn back on since.

I did a quick search on this forum for the same model tv and found a thread slightly similar to this. Located here: LG 55LS4500-UD Shutting down

Now they said they bought a replacement power board from ShopJimmy and it did not resolve their problem.

Not sure where to start with this one. Possible main board issue? Could it be the case of an LED in the panel acting up?

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

Measuring the voltages around the power board, the 24V line in the connector going to the main board is not reading anything. Only the two 3.5V lines are. Would the 24V line always read 24V or only if the tv is turned on?

[dick_barton]

Re: LG 55LS4500-UD: Not Staying On

What voltage do you have at PWR_ON (Connector P201) prior to and after attemping to switch on.

[Diah]

Re: LG 55LS4500-UD: Not Staying On

Measuring the voltages around the power board, the 24V line in the connector going to the main board is not reading anything. Only the two 3.5V lines are. Would the 24V line always read 24V or only if the tv is turned on?

its main boards issue, now this LG turn Off because there are no Signal, if you from Menu setting turn off Automatic Standby it will remain on with out signal.

here the service manual start to trouble shooting the main Boards at page 14, as this Coil ( L 3703 ) responsible on 3.3 V of Digital and analog signal.

[Moreno83]

Re: LG 55LS4500-UD: Not Staying On

Indeed a mainboard issue. Just saw the same tv listed with exact same problem. Cant find a signal on all hdmi. Probably bad solder under cpu

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

Thank you so much for the great replies all!

Diah, thank you for that awesome detailed service manual! I checked the L3703 coil and it is reading 3.4V. I then checked the IC3703 nearby which has three pins on the left side and one large pin on the right. The big pin reads the 1.8V while the three left side pins read from top down: 0V, 1.8V, and 3.47V.

Also, to answer your reply Mr. Barton. On the power board at connector P201, the PWR-ON pin reads -0.00 before trying to turn it on and when I try turning it on it stays at 0.00, but the - in front disappears.

Any suggestion on what to test next on main board or should I just go ahead and source a replacement board?

[Moreno83]

Re: LG 55LS4500-UD: Not Staying On

Do you have a flux? If so , place it under the cpu so it will flow the solder. Heat the cpu with a heat gun at close range for 3 minutes. You will see the flux bubble/move around the cpu and if your lucky it will solve the problem.

Will be wise to order a new mainboard just to be sure.

[dick_barton]

Re: LG 55LS4500-UD: Not Staying On

Also, to answer your reply Mr. Barton. On the power board at connector P201, the PWR-ON pin reads -0.00 before trying to turn it on and when I try turning it on it stays at 0.00, but the - in front disappears.

Any suggestion on what to test next on main board or should I just go ahead and source a replacement board?

It does look like a mainboard issue if PWR_ON is not going >2v when trying to come out of standby.

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

Thanks for the follow up replies! I do have access to flux actually. I am lucky enough to be a repair tech at an electronic repair store. The owner has the tools actually for doing small board repair on phones, particularly iPhones and Macbooks.

I attached a photo of the main board. I believe I already know the answer, but just to be sure, I assume the CPU is located under the black heat sink attached to it?

[Moreno83]

Re: LG 55LS4500-UD: Not Staying On

Yes thats correct! Reflow that cpu with of course the heatsink removed for about 3/4 minutes. Watch out that the board does not start bending.

Let it cool for 10/15 minutes

[Moreno83]

Re: LG 55LS4500-UD: Not Staying On

Btw , whats that switch near the white connector? SW200

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

According to the PDF that Diah posted, on page 27 it says that SW200 is part of the SOC_Reset. It reads 3.5V when the power is plugged in. There is no way of accessing the switch with the panel on the back of the TV.

[Diah]

Re: LG 55LS4500-UD: Not Staying On

SW200 for hard reset, just push it for 3 seconds long, tv will restarted as new Install.

between yours MB look some one before diagnosed fault IC101 and took the heat sink and play around, you can see there Silicon going out from both sides which in original LG don't use this silicon.

try reset it,,, reflow it, but in this boards which was under other hands, i suggest to replace it.

[Moreno83]

Re: LG 55LS4500-UD: Not Staying On

So somebody already reflowed that cpu?

[ReeceyBurger123]

Re: LG 55LS4500-UD: Not Staying On

I would say bga solder on this one seen it alot with these Lg XD engine Cpu based boards.

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

Ok, well I will try a reflow of the IC101 chip, but won't hold much hope. I have a hard time getting the TV to come back on again. No signs of a display at all, not even a standby light.
I pushed the reset button in though for 3 seconds to no change. I assume that it appears IC101 is the brain of the TV and might be why there is very limited signs of life in it.
Going into the store today and will reflow the chip there. I'll post back this evening with the results. Thanks again all.

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

Ok, no dice with the reflow of IC101. I will get another main board and go from there!

[ReeceyBurger123]

Re: LG 55LS4500-UD: Not Staying On

Ok keep us updated

[ECU_Techie]

Re: LG 55LS4500-UD: Not Staying On

** UPDATE **

Ok, well this is a success story. Main board replacement came in the mail today and it fixed the issue. TV is on currently and working great! Thank you guys for your input and help on this and I thought it would be nice to provide a resolution to this issue.