LG 50pk750-ua bad main

[x_orange90_x]

I just got this tv yesterday and it exhibit the exact same symptoms as the OP in the following thread:

https://www.badcaps.net/forum/showthread.php?t=48150

Power it on and the screen lights up, goes dark after about 2 seconds, and pressing any button lights up the blue led on the tv. The person in the above thread replaced their main board and it fixed the problem. I find that it's way too expensive to buy a replacement on eBay. There are "services" on eBay that claim to repair these boards, but the cost is still quite high.

My question is, what goes bad on these boards that these "services" are repairing? Bad IC? Poor soldering? If it's something that can be done at home I'd like to give it a shot.

I don't have any photos yet because I haven't opened it up yet.

[Diah]

Re: LG 50pk750-ua bad main

BGA could happened on OLD and new TV too... the threat you linked do the same as in POST #21 and #26

[x_orange90_x]

Re: LG 50pk750-ua bad main

BGA could happened on OLD and new TV too... the threat you linked do the same as in POST #21 and #26

Thanks for the reply! Ya I seen those posts about the BGA. I think I'm going to take the board to my brother to try and fix it. He has a soldering station and all that good stuff. He said he can heat it up and reflow it.

[nomoresonys]

Re: LG 50pk750-ua bad main

The lead-free alloy used for BGA solder balls has a melting point of 217ºC and requires a minimum reflow temperature of 235ºC to ensure good wetting. Maximum reflow temperature is in the 245ºC to 260ºC range, depending on complexity and density of the board.

[x_orange90_x]

Re: LG 50pk750-ua bad main

The lead-free alloy used for BGA solder balls has a melting point of 217ºC and requires a minimum reflow temperature of 235ºC to ensure good wetting. Maximum reflow temperature is in the 245ºC to 260ºC range, depending on complexity and density of the board.

I don't know what equipment he has but I know he repairs CRT TVs and monitors, and old video game consoles. He said he can do it.

If I were to install a small fan on the heatsink (if ample room), would I have it pulling air off or blowing onto the heatsink? I could probably wire it to one of the USB ports right?

[nomoresonys]

Re: LG 50pk750-ua bad main

It's nice if the fan fits inside, some cut a hole the shape of the fan thru the back cover right where the heatsink is and put it there, prolly a 5 volt case fan would work if you want to use a usb port of tv, I think blowing air directly on it is best.

[Diah]

Re: LG 50pk750-ua bad main

to the age of this TV and its known fault and the heat it generate 100% its reflowed before at least 1 time.. in this case if didnt work then need Pasta and stencil to reball , only Pasta will work not ball

[x_orange90_x]

Re: LG 50pk750-ua bad main

to the age of this TV and its known fault and the heat it generate 100% its reflowed before at least 1 time.. in this case if didnt work then need Pasta and stencil to reball , only Pasta will work not ball

I highly doubt it was ever serviced. I got it from an older couple and they said the HDMI went out first, so they used rabbit ears and then eventually that quit working too. Now it does pretty much nothing besides power on.

Random side question though, does anyone know if the stand has to be removed to get the back cover off? I hate how some TVs you have to lay flat and remove the stand to get the cover off. My 60" Samsung has an access panel that can be removed to get to all the boards while it stands upright.

[Diah]

Re: LG 50pk750-ua bad main

yes you need.. and a punch of screw LOL

[x_orange90_x]

Re: LG 50pk750-ua bad main

I just had my brother do a reflow on the BGA and replace the thermal pad. I'll report back after I've tested.

[x_orange90_x]

Re: LG 50pk750-ua bad main

Put it back together last night and it worked! I have noticed though that the image seems faded, lacking bright whites and dark blacks. Colors look good and the picture quality is great, but the tone/temp is just off. I messed with the settings and nothing completely fixes it. If there is only a single thing being displayed, for example the loading symbol in Mario Kart 8 Deluxe, it's very bright and vibrant. As soon as the rest of the screen is populated, everything gets dimmer and pale.

Could this be weak capacitors, or is it just an old tired panel?

[x_orange90_x]

Re: LG 50pk750-ua bad main

I have been reading about LGs having overly aggressive Automatic Brightness Leveling and/or Temporal Peak Luminance. I think that's what's happening with the dimming, but as for the lack of bright whites I still have no idea what that's about.

[diif]

Re: LG 50pk750-ua bad main

Poor quality reflow perhaps.

[Diah]

Re: LG 50pk750-ua bad main

Poor quality reflow perhaps.

+1 reflow not 100% succeed..
tell yours Brother to add load at the middle on the CPU,

[x_orange90_x]

Re: LG 50pk750-ua bad main

I'm reluctant to agree that it's from the reflow. Have you guys personally seen this happen? It looks something like blue light filter or Warm temp settings, but only over white. Everything else is vivid. And speaking of vivid, I find changing the picture mode from vivid to sport helped a lot.

All of these results are on a single HDMI and single source. I haven't had time to test OTA or another device/input. I will try later today to see if it's across all inputs.

[diif]

Re: LG 50pk750-ua bad main

I've not seen it as I have BGA rework machine with a bottom heater.
It reads like a poor job though.

[nomoresonys]

Re: LG 50pk750-ua bad main

Skip the vivid mode, that's what kills backlights early.

[x_orange90_x]

Re: LG 50pk750-ua bad main

Yeah, on LEDs I always set them to vivid and manually turn backlight down to about 70%. This is a plasma though, so no backlights to worry about.

[nomoresonys]

Re: LG 50pk750-ua bad main

Oh, my bad failed to register the P.

[x_orange90_x]

Re: LG 50pk750-ua bad main

I played around with it more yesterday. I connected an antenna for OTA tv and adjusted the settings more. It actually looks great now. The only real issue I have with it is the auto dimming. I can't seem to find any info online about a service menu for this tv, so I can't disable the feature. I have turned off the eco setting however. I know on the OLED models they have Temporal Peak Luminance and/or Automatic Brightness Leveling in service menu. Maybe LG locked the options in the plasma models 🤷