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Old 02-12-2013, 07:10 PM   #1
Hopsing64
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Default LG 42LK450-UB No pic/No sound

Hi,
I’m new to fixing TVs. I usually just stick to computers. I have an LG 42lk450-UB. It got hit with a power surge. The red standby light comes on when plugged in and when powered on it will flash twice and then turn blue. I get no picture and no sound. The backlights do not come on at all and I cannot see a picture when shining a light on the screen. I checked the caps with an ESR meter and they are fine. The two large caps (82uf 450v) are bigger than what I normally deal with so I don’t know the specs on them. I got a .22 on the ESR and in standby 168v and powered on 388v. I checked both fuses on the power board and the one on the t-con board. I measured all the voltages at the connection between the power board and the main board.
12v – 12.3 Err - .07
12v – 12.3 P-dim - .01
12v – 12.3 A-dim – 2.91
3.5v – 3.4 Inv on/off – 0.3
3.5v – 3.4 3.5v – 3.4
20v – 21.6 3.5v – 3.4
Power on – 3.2 20v – 21.6
20v – 21.6

Not sure what to test next. Thanks.
Attached Images
File Type: jpg main board.JPG (945.9 KB, 43 views)
File Type: jpg power board.JPG (1.83 MB, 45 views)
File Type: jpg tcon1.jpg (1.43 MB, 32 views)
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Old 02-13-2013, 08:24 PM   #2
Hopsing64
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Default Re: LG 42LK450-UB No pic/No sound

I was just reading Randteks post that included a "main board simulator jig" that he made. I made one and my backlights work. I also checked the fuse on the t-con board. It is good, but there is no power to it when the tv is off or on. Is there anything on the main board or the t-con board that I can test to see if it is one or the other?
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Old 02-13-2013, 09:16 PM   #3
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Default Re: LG 42LK450-UB No pic/No sound

"Inv on/off – 0.3" your main board is not sending the Inverter on signal. You can force it on using 3v source, once you get the backlights to come on, if other section of the main board is working, then you should see the pictures and get the sound OK, if not, then you have multi problems on your main board.
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Basic LCD TV and Monitor troubleshooting guides.
http://www.badcaps.net/forum/showthr...956#post305956

Voltage Regulator (LDO) testing:
http://www.badcaps.net/forum/showthr...999#post300999

Inverter testing using old CFL:
http://www.badcaps.net/forum/showthr...er+testing+cfl

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http://www.badcaps.net/forum/showthread.php?t=24809
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Old 02-13-2013, 09:43 PM   #4
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Default Re: LG 42LK450-UB No pic/No sound

I can only get the backlights to come on by jumping them when the main board is disconnected from the power board. If the main board is hooked to the power board, then no backlights.
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Old 02-13-2013, 10:13 PM   #5
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Default Re: LG 42LK450-UB No pic/No sound

What you have to do is to isolate the Inv on/off wire by cutting it and feed the one end that is connected to the power supply board with 3v to turn it on, that way the main board will get all the voltage feeding it and you will not have 3v backfeed to the main board. You can slice the wire back together after the test.
At this point I think you do have main board problem, should look and see how much it will be and hopefully the T-CON is not damaged either.

Last edited by budm; 02-13-2013 at 10:15 PM..
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Old 02-14-2013, 06:59 AM   #6
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Default Re: LG 42LK450-UB No pic/No sound

I snipped the inverter wire and hooked it to a 3.5v wire on the power supply. No backlight. But if I unplug the main board I get backlights. Main board and t-con are reasonably priced on eBay. Ill probably order a main board after work and see what happens.
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Old 02-14-2013, 08:45 AM   #7
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Default Re: LG 42LK450-UB No pic/No sound

"But if I unplug the main board I get backlights" That condition does not make sense since the power supply will need Power on – 3.2V (which is what you have on post1) from the main board to turn on the power supply.
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Old 02-14-2013, 04:07 PM   #8
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Default Re: LG 42LK450-UB No pic/No sound

Sorry. In my haste to get out the door this morning, I left out a sentence. I get no back light with the inverter wire attached to the 3.5v wire with the main board plugged in or not plugged in. I ran another wire from the 3.5v to Power on and got no backlights with the main board connected but get backlights when main board is unplugged.
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Old 02-14-2013, 04:21 PM   #9
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Default Re: LG 42LK450-UB No pic/No sound

I have a mainboard with a non-working tuner for that TV that I would ship you for the cost of postage. If it solves your problem you could solder your tuner onto the mainboard I send you. At minimum, it could narrow down if that is your problem. If you don't need to use the tuner, you could use the board as is for HDMI and component inputs. PM me if you are interested. I'd guess it would be less than $7 to ship it to you.

The coax had broken off of my tuner and I couldn't find just the tuner and ended up ordering a complete mainboard to fix mine. That is why I am left with a mainboard with a broken tuner. The coax connector broke off of the tuner.
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Last edited by DakotaKid; 02-14-2013 at 04:35 PM..
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Old 02-14-2013, 04:43 PM   #10
Hopsing64
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Default Re: LG 42LK450-UB No pic/No sound

This is my board number EAX64113202 (0). How hard is it to solder on a tuner? Where about you located? I talked to the owner of the tv earlier today, and he's having withdrawals from not having a tv for 8 days.
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Old 02-14-2013, 05:39 PM   #11
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Default Re: LG 42LK450-UB No pic/No sound

I am located in the Kansas City area. If my board solves the problem you could go ahead and buy a complete board if you wanted instead of soldering. If mine doesn't you'll know it's the other board you need and it only cost a few bucks to find that out.

I've replacd 4 or 5 tuners, all successfully. The most tedious part is desoldering the old one little by little, slowly lifting it as you go. You need some good desoldering braid so you can remove as much solder as possible as you go or it will take forever. Just take it slowly. Soldering it back on is easy.


At least this gives you an option to help problem solve.

Last edited by DakotaKid; 02-14-2013 at 05:43 PM..
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Old 02-14-2013, 07:36 PM   #12
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Default Re: LG 42LK450-UB No pic/No sound

How interchangeable are main boards? I see main boards on ebay from different size and different model tvs with the same part number as mine. Does everything need to be exact or is ik if just the part number matches?
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Old 02-14-2013, 08:10 PM   #13
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Default Re: LG 42LK450-UB No pic/No sound

No easy answer to that...it depends. Sometimes a board revision might add somethign as simple as a heat sink or more complex like a jumper wire or make a component change to correct something found in the field. Sometimes it's a vendor change. In this case, one thing that is clearly different is the tuner. My board has a micro-size tuner, about .5"x1" whereas your tuner is full size. Also, I notice that your board is December 2010 and made by LG whereas mine is June 2011 and made by HannStar. This all may or may not matter because it MIGHT be functionally compatible. I don't think you could ever get someone to say it would work, you'd just have to try it if you wanted. Problem is, if mine didn't fix yours you wouldn't know for sure if it is because your other board is bad or if it's an incompatibility between the versions of our boards. It would be a shot in the dark. Only you can decide if it's worth trying. I, of course, accept no responsibility if you do decide to try my board and it causes your TV to release its magic smoke. If you can find an inexpensive matching board I'd probably go that way.
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Old 02-15-2013, 03:21 AM   #14
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Default Re: LG 42LK450-UB No pic/No sound

Numbers stamped on boards, or on stickers on boards often cannot be relied upon as "part numbers" In some cases, the number on the board is the part number of a bare board, with NO components installed. For some manufacturers, the *actual* part number of the board is also related to the software/firmware configuration of the board. In cases like these, some boards may be interchangeable, IF you know the proper settings to change, and how to get to them. To have the highest likelihood of having the board you purchase work, it needs to be from the same model and version (if used) number.
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Old 02-15-2013, 07:08 AM   #15
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Default Re: LG 42LK450-UB No pic/No sound

Agree completely! And there is no consistent standard applied across or even within manufacturers. I will sometimes try a similar board while troubleshooting but as I advised Hopsing, that can only help if it DOES fix the problem. If it doesn't fix the problem you still don't know if your original board is bad or if it is just a revision in firmware/components/etc causing a functional difference in the "similar" board that is keeping it from working.
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Old 12-09-2015, 01:53 PM   #16
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Default Re: LG 42LK450-UB No pic/No sound

I have read quite a bit on this and am a little confused. I have the same TV with a similar issue. Power light is red. When the TV is turned on, it blinks slowly twice and then turns blue. I can unplug the cable from the power supply (caps and fuses test ok) and the screen flickers before going off. I read about jumping the 3v wire to excite the thing. Can I have a little more detail on this. Everything I read is that my main board is bad. I don't thing this TV is work the $100.00 for a used one on Ebay.

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Old 06-19-2019, 07:59 PM   #17
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Default Re: LG 42LK450-UB No pic/No sound

Reviving this old thread as I'm having the same issue with the same model. LG 42LK450 - standby light comes on red and turns blue when power is turned on but no picture. Voltages on the DC side of the power board are almost identical to the OP except I only get .03v on Inv On/Off when powered on. Main boards for this model seem to be becoming extinct, and the few that I've found run about $100 and I just don't know if the TV is worth that. So I was curious if anyone had one laying around they wanted to part with cheaper than that... or if someone could start me in the right direction of identifying the component on the main board that's causing the problem? Thanks in advance.

Last edited by homeslice976; 06-19-2019 at 08:01 PM..
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