LG 55lm4700-ue - Black screen, no image.

[grimacelord]

Came in with no power at all. Customer said a squirrel chewed through a power line in their house and it knocked out a whole bunch of their electronics.

I found multiple bad components on the power board so I just replaced it because it was cheap enough and it did power on after that, but just to a black screen. So I checked out the TCON board and found the fuse was visibly burnt. I found the same valued fuse from another TCON board in my scrap pile and replaced it and tried to power on, but it just blew that fuse as well. So I ordered another TCON board.

Replaced TCON board and still, powers on, but black screen. Fuse did not blow this time. I started checking for shorted capacitors on the TCON board and found three: C208, C209, and C210. I unplugged the left ribbon cable leading down to the panel control board and tested those capacitors again and they were no longer shorted.

So I disassembled the display enough to get to that controller board for the panel and started checking the capacitors for shorts as done by this guy in this YouTube video, (in fact, that's the same TV it looks like. Same layout and appearance and everything. Same problem, too.) but was unable to find any like he was able to in his video.

There are lots of resistors and a few diodes on this controller board as well. I used a magnifying glass to visibly inspect them to see if any had the typical small "pin-hole" burns in the tops of the SMD resistors, but found none. I haven't checked them individually because there is a ton of them and before I put more time and effort into this, do you guys think it's a lost cause or is it worth the time to check each one? Some of them have their value printed on the resistor, but others don't. Without the service manual or schematic or something, I don't know how I'd know what to replace them with even if I did find some bad ones. I tried looking for it, but was unable to find it. So rather than sort of navigate blindly and potentially waste a bunch of time, I thought maybe I'd ask here for some advice before I bothered with it again.

Or maybe I am going about this all wrong entirely. If somebody could help me out, I'd appreciate it. Pics attached.

Voltages:

PWRON: 3.39
24V: 24.62
GND
GND
3.5V: 3.51
3.5V: 3.51
GND
GND
12V: 12.14
12V: 12.14
12V: 12.14
P-DIM2: 1.31

[Diah]

Re: LG 55lm4700-ue - Black screen, no image.

you need to go back to yours OLD PSU and check on which V Line was toasted 12 or 24 V. follow this on your MB, i believe this strike toasted same line on MB

BTW you didn't mentioned the LED Back light.. they are on or off?

[budwich]

Re: LG 55lm4700-ue - Black screen, no image.

so from your "unplug the tcon to panel cable" test, you found that "shorting area". You could try doing a "tape cutoff" method (bit of tape on the tcon connection to block the signal for those pins) and see if this helps get a picture. Lots of posts using this technique. It may not work as it is possible that the smd component on the edge board may still have too much impact on the remaining pins / tracks.... but it costs nothing but time to try.

[grimacelord]

Re: LG 55lm4700-ue - Black screen, no image.

you need to go back to yours OLD PSU and check on which V Line was toasted 12 or 24 V. follow this on your MB, i believe this strike toasted same line on MB

BTW you didn't mentioned the LED Back light.. they are on or off?

Backlights are on. Work fine.

I'll have to dig out the original power board.

[Diah]

Re: LG 55lm4700-ue - Black screen, no image.

Backlights are on. Work fine. .

in this case if you disconnected one by one ribbon cable between T-CON and Panel and there are no half white screen. then dig at MB the case no LVDS Sig / Freq going out from MB