50" LG Plasma TV issues

[vortalexfan]

Hello Everyone a friend of mine gave me their old (from 2012) 50" LG Plasma Smart TV model 50PM6700 that when you go to turn it on it clicks on like its going to power on and you get a grey colored screen for about two seconds with a flashing red light and then the TV just clicks back off with a steady burning red light again.

I had looked up the symptoms online and one forum said that the power supply board had an issue with C802 on the board and that replacing that capacitor fixed the problem for most people and some people it didn't.

I was wondering if anyone else on here had a similar experience with a similar TV and had any ideas as to what would cause these aforementioned symptoms.

Thanks.

[dr.ido]

I don't know that exact model, but the following applies to a lot of LG plasma TVs -

Disconnect the main board (the one with the HDMI /etc inputs on it) from the power supply.

Connect power - without the main board connected it will power up. If you get the grey screen and it now stays on then the power supply and sustain boards are probably ok.

Find the AUTO_GEN pins on the controller board - short these pins and the controller board will generate test patterns. This will confirm that you panel, sustain boards and power supply are good.


Most of the time the main board is the problem. Often you can reflow the main IC on the mainboard with a heat gun and this will fix the problem.

[vortalexfan]

Originally Posted by dr.ido

I don't know that exact model, but the following applies to a lot of LG plasma TVs -

Disconnect the main board (the one with the HDMI /etc inputs on it) from the power supply.

Connect power - without the main board connected it will power up. If you get the grey screen and it now stays on then the power supply and sustain boards are probably ok.

Find the AUTO_GEN pins on the controller board - short these pins and the controller board will generate test patterns. This will confirm that you panel, sustain boards and power supply are good.


Most of the time the main board is the problem. Often you can reflow the main IC on the mainboard with a heat gun and this will fix the problem.

Thanks for the tips. I found the auto_gen pins you were talking about, mine unfortunately had no pins present and it was marked ext_auto_gen on mine so it seems mine wasn't meant to automatically generate test signals. But I'll still try what you said though about testing the tv without the mainboard connected and see how it works. How would I reflow the solder around the main chip on the mainboard with a heat gun? The main chip looks like it might be surface mounted and has a large heatsink over it that's covering the solder connections for the main chip to the mainboard.

[vortalexfan]

OK So I replaced the capacitor that I had read elsewhere that was supposedly the problem and it still is acting up, so I tried powering on the TV without the main board hooked up to the TV like you suggested and it wouldn't even power on or even attempt to power on without the mainboard hooked up.

Here's a picture of the TV's mainboard posted below. Is the big black square heatsink in the middle of the mainboard the main chip you were talking about? If so then I don't see how I could reflow the solder on that chip because of it being surface mounted plus the heatsink would probably destroy the chip if I hit it with a blast from the heatgun.

[dr.ido]

If the power supply is ok it will start up without the main board connected - Obviously without the main connected the LED will not come on.

If the power supply does not start then you either have a bad power supply or one of your sustain boards is shorted and that is causing the power supply to shut down.

Apply power with only AC in connected to the power supply. If it is ok it will start up and you can measure the voltages. If all the voltages are where they should be then your power supply is probably ok.

Connect the power to the sustain boards one at a time and repeat the test.

EXT_AUTO_GEN is correct. Short these points (I just poke a piece of wire in the holes) and the controller will generate various test patterns.

It is the main chip under the heat sink. I remove the heat sink, apply liquid flux around the edges and heat it with the heat gun for a few minutes. Then I let it cool for a while and hook it up again. Success rate so far is 7 out of 10. If they start up I leave them running all day/night. All the ones that were still working the next day went out to customers and didn't come back. Those that failed did so pretty quickly.

That said, there is no point heating the main board if you can't get it to power up and make test patterns.

[vortalexfan]

Originally Posted by dr.ido

If the power supply is ok it will start up without the main board connected - Obviously without the main connected the LED will not come on.

If the power supply does not start then you either have a bad power supply or one of your sustain boards is shorted and that is causing the power supply to shut down.

Apply power with only AC in connected to the power supply. If it is ok it will start up and you can measure the voltages. If all the voltages are where they should be then your power supply is probably ok.

Connect the power to the sustain boards one at a time and repeat the test.

EXT_AUTO_GEN is correct. Short these points (I just poke a piece of wire in the holes) and the controller will generate various test patterns.

It is the main chip under the heat sink. I remove the heat sink, apply liquid flux around the edges and heat it with the heat gun for a few minutes. Then I let it cool for a while and hook it up again. Success rate so far is 7 out of 10. If they start up I leave them running all day/night. All the ones that were still working the next day went out to customers and didn't come back. Those that failed did so pretty quickly.

That said, there is no point heating the main board if you can't get it to power up and make test patterns.

OK So when the mainboard is disconnected from the power supply does the TV power up on its own without needing to hit the power button? If So then I think the TV is working like it should and it is like you said and is just a matter of needing to reflow the solder on the main chip on the main board because with the mainboard disconnected from power and the TV hooked up to AC Mains the TV makes the sound of powering up (a clicking noise) and it doesn't make the second clicking noise of powering off after a few seconds like it does when the mainboard is attached to the power supply board. the only problem is that I don't have anything small enough to insert into the auto_gen jumper holes to see if it produces a test pattern or not.

So I'm assuming that when the TV powers on without the mainboard in the circuit the screen is supposed to be blank unless you have it do the auto_gen function?

Also what setting did you use on your heatgun to reflow the solder on the main chip on the mainboard, in otherwords what temperature setting did you use? Because I don't want to get it too hot and I don't want it too cool either.

[dr.ido]

Yes, with the main board disconnected it will power up as soon as it is plugged in. If you don't have the ext-autogen pins connected there will be no picture. You may see a grey screen depending on how bright the lighting in the room is.

I strongly recommend using the ext-autogen to confirm that your panel is good - Nothing is worse than than fixing one fault only to find your panel has dead lines/pixels or a bad buffer - though if it was your personal set and you know the picture was fine before the main board failed you can rule this out.

I have used a hot air station set at 350 degrees celcius and a generic hardware store heat gun that isn't calibrated set to max.

[vortalexfan]

Originally Posted by dr.ido

Yes, with the main board disconnected it will power up as soon as it is plugged in. If you don't have the ext-autogen pins connected there will be no picture. You may see a grey screen depending on how bright the lighting in the room is.

I strongly recommend using the ext-autogen to confirm that your panel is good - Nothing is worse than than fixing one fault only to find your panel has dead lines/pixels or a bad buffer - though if it was your personal set and you know the picture was fine before the main board failed you can rule this out.

I have used a hot air station set at 350 degrees celcius and a generic hardware store heat gun that isn't calibrated set to max.

Yeah I bought a $20 dual temperature heatgun kit complete with all of the different attachments and what not and I was using it on the low setting (1000W 700°F) which didn't seem to be hot enough to melt the solder so I used it on the high setting (1500W 920°F) as per your suggestion and it finally melted the solder for me so I think it might finally be fixed now just need to plug it back into the back of the tv and see if it works now.

[vortalexfan]

A little update, it seems that even after reflowing the solder under the main chip on the mainboard on this TV 3 times it still refuses to power on, but the good news is that I know for sure that a mainboard failure is definitely what's wrong with this TV because I disconnected the mainboard from the power supply board and jumpered the test pattern generator jumpers and the TV Screen lit up like it was supposed to, no bad pixels or anything, which means everything else on the TV works like it should just not the mainboard.

And since the TV didn't come back to life after 3 attempts at reflowing the solder on the main chip on the mainboard I'm kind of wondering if the main chip itself isn't bad which if that's the case I will probably just have to keep an eye out on ebay for another replacement mainboard for this particular model of TV and hope that the replacement board still works.

UPDATE: I didn't have to look for very long as a mainboard for this tv just showed up on ebay for sale today for $60 or best offer and I submitted an offer to the seller, so hopefully I'll be able to get this TV up and running by the end of this week if the seller accepts my offer.

Also I looked up a manual for this TV on the LG website and apparently this is a 3D SmartTV!

[vortalexfan]

UPDATE: I got the new board installed and the TV is working great!

I even ordered the remote for it and a set of 4 Passive 3D Glasses for it and so far I have about $50 into the TV which isn't bad!

I've been watching Star Trek Reruns on it and they look great on it because of Plasma's inate ability to mimic the color tones of the old CRT TVs.