LG-50PQ6000 clicks and clicks and clicks

[Baileybum1234]

Hi guys,

Im new to this forum and it looks totally cool.

Just to explain my background. Im an audio visual engineer and have an electrical background.

BUT (and a big but) I dont have mutch experience with the inner sides of plasma screens.

I was sent to site to swap out a faulty screen and asked the customer if they wanted me to skip the old unit. Well lets just say I saw this as an opportunity to bag myself a decent TV and learn something about the inside guts at the same time.

The fault seams common it doesnt come out of standby just clicks and clicks and clicks.

I have had a good look inside and all the capasitors on the PSU board look fine. I have ran a DVM across the pins and all voltages appear to go high and then low with the clicking.

Seams to be a tiny relay clicking.

I have removed the PSU board and plugged it in and the same is happening. I dont know if this was a test or not.

It could be a number of things I just need a little prod in the right direction to fault find it a little further.

Cant wait to get stuck in and thanks in advance for any help!

Jarrett

[imp]

Re: LG-50PQ6000 clicks and clicks and clicks

Welcome to the forum Jarrett

Please see this thread for more info about similar problems to LG plasmas:

https://www.badcaps.net/forum/showthread.php?t=18008

From post 14 and forth, it may be the AC detection circuit that makes your set to repeately click.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Nice one imp I will check it out. :0)

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Ok cool it could just be a case of shorting out the 2 optocouplers. My PSU board is different to this one. Its pcb p/n 3pagc00002a-r.

Is there a test I can do to identify the 2 optocouplers i might need to short on the PSU board I have?

Is there a way to test the optocouplers are working or not?

and what do the AC detect optocouplers do? other than detect AC :0)

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

The optocouplers tell the TV it's still plugged in.

You need to check if the AC-DET pin is a solid, stable 5V or 3V. If it is, then your problem is elsewhere.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Exellent thanks Tom. I will check this tomorrow.

Is it a daft question to ask why the TV needs to know why its still plugged in. I guess it sends a signal to an IC or something????

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

Exellent thanks Tom. I will check this tomorrow.

Is it a daft question to ask why the TV needs to know why its still plugged in. I guess it sends a signal to an IC or something????

If the signal goes, it gives the TV time to mute the sound to prevent a "crackle" or "pop" being emitted from the speakers as the audio circuits can go a little "wonky" when power is suddenly removed from them. The fix will mean the speakers will make a pop sound when turned off (unplugged, not put into standby) but it's not a bad thing just a little annoying.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Can they not just be replaced? or is the problem elsewhere? and this is a bodge?

Cheers

J

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

Can they not just be replaced? or is the problem elsewhere? and this is a bodge?

Cheers

J

It is a bodge, and no, I haven't figured out how to fix the issue yet, though I also have a blanket rule on not to pick up any LG "xxPC" or "xxPX" plasmas (unless I get them really cheap) because of the damn sparklies issue which is nearly impossible to fix.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

So the sparklies issue is something unrelated?

I would expect the optocouplers to be driven by something else? I havent been able to get a decent circuit diagram of this PSU board. I would hazard a guess there all simular?? What normally drives the optocouplers?

J

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

So the sparklies issue is something unrelated?

Yeah, it affects all older LG plasmas and is repairable, but expensive, requiring a new control board.

I would expect the optocouplers to be driven by something else? I havent been able to get a decent circuit diagram of this PSU board. I would hazard a guess there all simular?? What normally drives the optocouplers?

J

No schematics available as far as I can tell... The optos are normally driven by a voltage reference/comparator like the TL431, I suspect this may play a part in the failure as Budm and others have found these to fail before, but I'm not certain.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

AC detect pin is definately unstable between 5v and 0v in line with the clicks (relays) maybe 1 second on then off, then on then off ect.

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

OK, that looks like a problem. Check also your 5V STBY and 5V or 6V main voltage.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Ok there is a 5v STBY voltage that fluctuates from 5.2-4.8-5.2 and back around the time the relay clicks every second or so.

On the same multipin connector all of the 5v supply lines are dead and there is another larger multipin connector on the other side of the PSU board and that has 2 pins marked M5V?? there reading 0v DC also.

Am I right in saying the 5V supply is dodgy?

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

No, I think that is fine, and you have the AC detect problem. Can you share a pic of your PSU, from the top and bottom, in very good detail (2000x2000 or smaller, but the bigger the better.) I will try and highlight where to make the mod.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

ok think there attached. I assume your wanting to see the opto isolators so have tried to zoom in on these?

Thanks for your help by the way mate.

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

Boring night in uni dorm at the moment. Can you highlight the AC det pin for me? I can't quite see it.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Ok dont know if this will help. Boring night in dorm? What you studying electronics?

[tom66]

Re: LG-50PQ6000 clicks and clicks and clicks

I am studying MEng Electronic Engineering at Leeds, this is my first night . I can't see the traces on that board near that pin. Can you try taking a picture in sunlight or floodlight room - instead of with a flash? That usually works well.

[Baileybum1234]

Re: LG-50PQ6000 clicks and clicks and clicks

Ok that didnt work but you can see the identification on the board. Also hope this marked it for you.

Jarrett