Repair of LG 42LW5700 TA, LED TV, Part 1

I take a look at a faulty TV that does not power on fully, and diagnose the fault(s). I even reverse-engineer some of the back-light circuit.

[@Allan-]

Hi Richard, I watched your Videos on this because my 42LW5700 had just failed this morning. I found I had 3.5 volt, 12 volts and also Power on rail where working, but the Inverter signal was OFF, I had no Sound No Video, no Backlight. It pointed to the Main Board, I tried using my Heat gun to reheat the Main BGA Chip , but had no luck, so I did the Bake it trick, 200 deg for 10 minutes and after leting it cool for 30 minutes, reinstalled the Board and it worked !! Now the test will be to see how long it will last. Thanks for your Videos, they helped

[@richardrudek01]

Cool. I'm glad you were able to get it working (temporarily) again. By the way, I assume your 200 deg reference was in Fahrenheit not Celsius? Having said that, you might be able to prolong the operation by reducing the number of thermal cycles the main BGA is subjected to, especially large and rapid ones. For example, for many people, the largest thermal cycle will occur during first switch on after a cold night - as in your case. Keeping it on all the time might be one way to do that... :) Just to be clear, you should be preparing to replace the TV, and *NOT* replace the main board - unless your aim is to experiment... Good luck.

[@webtax]

baked in an oven a similar mainboard of a 42lv5500 last december, lasted 3 months now is dead with again (same symptoms as yours and as before), tried with a heat gun this weekend since it's less of a hassle but no good so far. Might try again the oven one last time.

[@Allan-]

No its 200 Deg Celsius, Melting point of Solder is 188 Deg , So at the temp the idea is to remelt all the joints. At 10 mins, you turn off the oven and open the door, DO NOT move the board, or bad things will happen. But it worked, nothing melted, basically the surface tension of the solder will hold the components on, of cause the Board is placed in the oven with the heavier components on top and its sitting on top of some cardboard. The LCD originally failed after it had been for an hour or so, it was not from a cold start. At first I assumes it was Cap failure on the Power supply board but they where all ok. It is an experiment and It will be interesting to see how long she keep going.

[@richardrudek01]

Thanks for clearing that up. As I probably said in the video, my concern was the plastics in the connectors. Surface mount connectors *"should"* survive a reflow. But you have to know your plastics for any through-hole types - Power, speaker, etc. Moreover, looking at the PCB silk screening, there are markings that I would normally associate with boards that are wave soldered. But the *lack of* obviously glued surface mount components and wicking pads left me scratching my head. I should probably take a closer look (with magnification). Having said all that, I did want to restrict any reflow specifically to the main BGA package, as opposed to reflowing (potentially) everything. Ah, tinkering is fun...

[@RioBautista]

Thank you Richard for these series of videos. I was able to save my LG LED TV because of this.

[@mehdisaeedi2404]

very very very tnx, god blase u, you helped me to save more than 130$, i just do the Part 3

[@withamara3206]

thank you for your help. can you help me find the motherboard? do u sell it?

[@miguelmdn7]

Mister, where can I get a new main board of Lg 42LW5700 ?

[@romniyepez5206]

Hi, where can I find the mainboard for this kind of LG 42LW5700 ? Thanks in advance.

[@richardrudek01]

Ah..., Google is your friend; maybe... I am *NOT* in this *Business*, so I have no rock-solid answers for you. The problem here is that whilst you might be able to buy a replacement board, unless it is from a reputable source [1], then your throwing good money after bad. [1] One assumes that an LG authorised repair centre could get access to *Genuine, **_unused_** parts*. But the problem is that these places are Businesses, presumably for profit. So with old(?) gear like this, what are you likely to get...

[@alessandralima4165]

Thanks @Richard Rudek, Romni and I took our TV to Local LG's repair service....though somebody from Panama used to call us to follow up the issue...finally they call us yesterday telling that LG doesn't support any more this Model... :-( well...from now on...Sony or Samsung for any electronic device...

[@sajjadmirzaee17]

Hi I am a repairman living in Iran Please help me fix the TVs LG 42 W TV, only its red standby LED light is on and it does not turn on anymore ... I tried to control the remote and the buttons, but it did not turn on Please tell me how to start troubleshooting Thank you very much

[@nahumhernandez6986]

Hello Richard I have a LG 47LW5600 it when off, and it can not turn on... Just red Led is ON, when I press power it bling 2 times and LED goes white but screen still black no image and not sound... Power board and main board looks same as the ONE in your video... Do you have any idea of the failure on my TV. I will appreciate your help.

[@richardrudek01]

Obviously you can take it to an LG Service centre. But if you're capable of repairing, which I can't tell from your profile, then I'd try hooking up a Computer running a terminal program to the TV's RS-232 port, like I did starting ~8:25 in part 4. You will probably need to search for the details for your TV. Take a (cautious) look at the Russian site. Depending upon which firmware version your TV is running, pressing the "F9" key in the terminal program enabled Debug Messages from the TV, and this was from quite early in the power-up of the TV. Though, from about version 5, the debug messaging could no longer be enabled by pressing the "F9" key. Here is a snippet of the debug messages: *Enabling display debug message* 000011.585198:tPostAdd] MAIN_DoPostAddonInitTask Done! Now task is exiting(c4986c) OSA_DeleteTask(taskId = 67) called, tId = 67 _OSA_cleanup_handle. clean thread (67:tPostAdd) 000011.640080:tPostCmm] MAIN Post Common Init Done! 000011.640206:tPostCmm] Stop syslogd... 000011.668631:n1_003 ] *** 00:00:10.545 astmlib: 1 Re-scheduling TSM-disabled watchdog timer 0/15/45 000013.669483:n1_003 ] *** 00:00:12.546 astmlib: 1 Re-scheduling TSM-disabled watchdog timer 0/15/45 000015.669106:n1_013 ] dispRect is set to Full Screen[0,0,1920,1080] ... ...

[@cat-lw6kq]

be careful if your probe slips and shorts out something, I used to work in a tv repair shop and I can tell you bad things can happen.

[@PauloCesar-yn1uo]

Bom dia gostei muito de ver o seu vídeo do jeito que vc explica , por favor mim ajude , tenho uma tv LG 42lw4500 tem áudio mais não tenho imagem, e eu não tenho esquema dela. Onde posso encontrar esse esquema PCB P/N: EAX62865401/8 REV1,0 e qual é o valor desse resistor 102 na placa, por favor traduzir em português

[@rayhindle642]

Hi and sorry to.be negative but you need a mike, sound level too low.........Ray H.

[@chrismath007]

Hi, I have same TV for repair. No Picture. No Sound....Backlight is not turning on. Backlight supply 36V is there. Power and standby functions are normal. Any clue? Thanks,

[@richardrudek01]

Sorry about taking so long to respond, but basically you need to check that you get the DRV-ON signal from the main board. Also, please read my response to roket iskandar.

[@eonflask8904]

Hi I would like to know if you still resolve your issue?

[@waliwalow7180]

Hi ! I've a problem with my TV LG 42LG2100 wich turns off after 2 hours of working and shut down after. I must wait for while before re use it and it's works again. Can you help me please ? Any advise ?

[@richardrudek01]

Unlikely. I don't know anything about this TV - I'm *NOT* a TV Tech. You might try finding and joining forums that do. I can't stand 'em, to be honest. Which is why I learn this stuff myself... Sorry.

[@MichaelGaza]

hi, i have the exact same LG tv... 42lw5700. just this morning the screen went black/grey with some vertical white lines in the middle. i can hear the sounds of the channel it is on but i can't see anything. do you have any idea as to what needs to be replaced here? thanks!

[@richardrudek01]

Two months ago. Wow. I don't know whether I should reply now or not. Sorry. But for anybody else, the fact that you get (good?) audio and appear to be able to operate the TV, just not see the picture, then this obviously is not a main processor issue, like in my repair video. It's *possible* it might be a main board problem, *but* it is more likely to elsewhere. Did you end up fixing it, and if so what was it ?

[@MichaelGaza]

hi. thank you for replying. I went to LG's authorized repair shop in my location and they say it's a panel board problem. And since it's a 3-year old TV, manufacturers do not make parts for it anymore. It's really sad that big companies do not make products like they used to... where replacement parts are always available. They're just in it for the money.

[@richardrudek01]

Yeah, it's real problem that I wish laws would force manufacturers into replacing them, regardless of their stated Warranty periods. In Australia, we have consumer protections that you can't (legally) avoid. But it is a pain to get specific answers to questions like, how long should a TV be expected to last. If I were to use my experience with CRT TV's, then the manufacturers should be liable for 10 years. Obviously this assumes that the TV simply sits on something that is not subjected vibrations, or flying objects (eg remote controls...). But if the manufacturers were forced into this, it would be interesting to see they solved this. For example, would we see them stop using Lead-Free solder; Would they stop using BGA packages, and/or making the manufacturers of BGA devices (like Broadcom) liable, etc. If you'd like a bit of laugh, I'm reminded of Dave L Jones of EEVBLOG video about his *Plasma* TV's panel problem. Some of the "bonding" technology is very similar to what's used with LCDs: EEVblog #52 - Panasonic Plasma TV's Suck (and a Teardown) kzbin.info/www/bejne/fIncY51-g9WplZI

[@MichaelGaza]

yes, exactly. what do you think i should? just replace the main board?

[@richardrudek01]

If it's a panel problem, then No. The Service Manual for this TV, does tell you to replace the Main board as part of the troubleshooting process. But that assumes that the fault is due to improper rendering done my the Main board. But if the repair centre continued the diagnosis, they would have tried a Main board, and then the TCON board (the thing under the shielding, where the stand is). As far as I can tell, after that, it is then the display panel itself. For example, in Dave's video (~ half way through), he isolated the fault down to one of the (many) panel drivers. It's probably a similar thing here, but I don't think we get any connectors that we can unplug to diagnose this any further. I haven't pulled this TV apart enough to know.

[@karanpandya2832]

Sir my TV not starting relya no red indicated blinking but TV not starting plz help power problem aur (MB) mothar board problem

[@eddejesus5420]

Model number 42lw5700-ue the screen got distorted to no picture but it still has sounds.

[@pasmas3217]

did u find anything about fixing it? i got 42lw570s, with similar problem. no picture just some lines that never move, but it still has normal sound any info (cost official and or unofficial, (location), diagnosed problem source...) would be welcome thanks

[@Nimbelwimbel]

Hi Richard, I´m having two LG 47LW4500-ZB with defect backlight, but same power supply like your 42LW5700 inside / main board looks different. For further details and questions I would like to send you an annex with your schematic and my measuring results by email. Is it possible getting your adress? Thanks in advance. Christoph

[@richardrudek01]

Apparently, Google\KZbin does have a private messaging system (different from the commenting system). You just need to "Confirm your name" [1] on your channel, and then I should we should be able to private message each other. But only to point... As your using the schematic I drew up in the first video (and your still alive), then it's fair to say this would be more of a peer-to-peer conversation. I do not like talking to "helpless" people - ah, there are those people skills, again... [1] From the help system: *Send and receive private messages* You can send and receive private messages from members of the KZbin community. The messages system displays your name and photo next to your message, so before you can use it you need to confirm your name on KZbin. Learn more about confirming your name. *Send private messages* Go to the channel of the person that you want to contact. You can do this by clicking their channel name underneath one of their videos. Click the About tab. Click Send message. Type in your private message and click Send. *_Note: If a channel doesn't have a confirmed name on KZbin, it won't be able to receive private messages and you won't see the "Send message" button on the channel._*

[@Nimbelwimbel]

thanks for your quick answer. i did as you said and confirmed my profile name at youtube. unfortunately i can send everyone but not you a private message. any solutions for that problem?

[@richardrudek01]

OK, it looks like the help for private messaging is either wrong and/or incomplete. It might also have something to do with Google+. Not sure. Either way, I found that I can private message my Subscribers. Via "My Channel", from *MY* subscribers list, I clicked the balloon-comment icon on the right of their entry, etc. I could not find a private message thing on your KZbin homepage. So I subscribed to you, just in case you can't respond to my message, using your Subscribers list, like I just did.

[@karanpandya2832]

MODEL NUMBER 42LW5700-TA LG

[@clement3015]

tem como traduzir para português

[@Bennybruss]

my tv of this exact model just stopped working and won’t turn on, red power light just keeps getting bright then going off like a pulse.. any help please anyone??

[@NSVMohith]

You will need a new board.

[@carlosa881953]

Too bad, the Spanish subtitles don't work.I am from Colombia (South America).

[@igoniskandar]

why lg xd it's must be to heat . i was second time to heat it. give information thx mr.

[@richardrudek01]

Hah. Skimming the videos, it looks like I might have left out some relevant information leading up to me heating the "XD" chip. The LED backlight is controlled by the "DRV-ON" signal from the main board. So without this signal, the backlight stays off. In other words, my problem was *NOT* with the Power Supply or the backlight circuit, but with the main board. At this point, many people buy a replacement main board. But this TV was not worth the risk or cost. But it was worth experimenting, so tried "fixing" the main board. After tinkering with the serial interface commands, I suspected an issue the main CPU and started looking over the main board. This is when I realised that the "XD Engine" chip is basically the brains for the whole TV, and it was a large and hot BGA device. This is a significant piece of information because it is well known that large and hot BGA devices have reliability issues after about 1000 thermal cycles. Tin whiskers can also be an issue for devices under stress, such as those with spring loaded heatsinks. So I tried to "reflow" the chip using my cheap and inadequate hot air tool. I *now* know that the "XD" chip (an LGE35230) has 656 balls at a pitch of 0.8mm. What I did should not have worked. But for some reason it did. So I thought it might have been a Tin whisker issue. Actually, it only worked for about one week. This is why I tried it again. But this time, I tried to more closely follow the correct way to reflow this BGA device - preheat, soak, reflow and cool down. Amazingly, even though I did *not* actually achieve a reflow of the "XD" chip, the TV started working again. So this might actually be an internal failure of the chip, and not (just) the BGA interface. Having said all that, even though I got the TV working again, I have not returned the TV because I know it will fail again. Besides the TV was replaced with a new Samsung 40". At this point in time, there is zero chance of me replacing that LGE35230 BGA device, and even if I could, I would be highly suspicious of any chips that I could get to replace it. Somewhere along the way, the NVRAM got corrupted. So the power-on Logo is now some random rubbish, and the back light won't turn on with full power anymore - about 50 Watts instead of 120 Watts. So whilst the TV is quite usable, it will need some more work to correct these new problems. However, I have moved onto other things. I might follow up with another part or two, later. We'll see.

[@igoniskandar]

+Richard Rudek thx alot mr.

[@Daniel-love]

3d smart tv lg 42lw5700 light blinks not start if anyone have solution please let me know

[@amjedmustafa7342]

Did you solve the problem ? How ?

[@SangNguyen-rk7pq]

me too..help me..i live in Vietnam