Need Some Repair Advice LG 47LG50

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Tried to edit previous post to add pics of the inverter boards.
I will get the LCD number for you.
Thanx!

[selldoor]

Re: Need Some Repair Advice LG 47LG50

Well I can see a number of fuses and a lot of zero rated resistors which can be checked like fuses. So they are all an easy test - meter on ohms should all test the same as touching probes together. Test all the fuses first make sure you dont miss one

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

I went over them under my benchtop scope and checked all the ones I could see. That was the first thing I did. All good. I spent no less than 20 minutes on each board. I even pulled off one of the XFRMR's just to see how it is configured. I like to really dive into what I am doing. This is a habit i have from restoring vintage audio gear. I do not like to mis anything and especially like to see what makes it tick!
When I get this set up and running once the problem is solved you can bet I am going to be making a BOM for Mouser to get all replacement caps.

Thanx,
Bud

[johnboy1313]

Re: Need Some Repair Advice LG 47LG50

You may have a cracked bulb or one or more that are on their way out. If you don't get anywhere with the inverters try opening the panel.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Here is the panel that's in this TV:


It's a Chi-Mei panel. V470H1-L03

Thanx!

Bud

[budm]

Re: Need Some Repair Advice LG 47LG50

OK, per spec: "Note (4) When inverter protective function is triggered, ERR will pull low" You do have HIGH of 3.3V. I would it to go low and stay low after the backlights come on and then go into protective shut down to tell the main board it has problem. Need more thinking on this one. You can possibly have bad lamps, but I would think it will stay (latched) low.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Well then,
I think in the interim I am going to wait on that Chinese CCFL lamp tester I ordered today and then get back to it. Don't really want to rip the thing apart if I don't have to. If you have anything else you can add to this in the meantime please, by all means!
I did pull all of the lamp connectors from the inverter boards and tried firing it up. No difference. Do these inverters need some sort of continuity between the tubes to keep the error logic from happening?

I'll get back to this in a coupla weeks. I need a breather from it anyway. Too many pressing jobs on the bench and this was just a WTF anyway job since I dug this out of the trash anyway.
Thanx again to all who have helped thus far!
Bud

[69sixpackbee]

Testing Inverter Function With External Triggering Supply?

I have a quick question that might help others with a "general" inquiry about inverters. I am trying to diagnose a possible inverter issue with this 47" LCD television and in the meantime I was thinking of temporarily cutting the BL_ON wire and supplying it with another external 3.3VDC source to see if the lamps illuminate briefly. I will also temporarily disconnect the ERROR line as well for the test. Is this okay?

Thanx,
Bud

[budm]

Re: Need Some Repair Advice LG 47LG50

That will be fine, some people use 1K resistor between the 5V STBY power supply pin and the BL_ON Pin (cut or remove the wire going back to the main board of course).
There are circuits on the inverter board to detect if one of the lamp is not connetced, of once the lamp is fired up with starting voltage but fail to stay on, or the lamp draw too much current, that will cause the inverter to go into shutdown protection mode, so it will only take one bad lamp to be bad to shut down the circuit. This detection happens in the first 3 seconds if something is not right in 3 seconds, it will go into shutdown.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

That will be fine, some people use 1K resistor between the 5V STBY power supply pin and the BL_ON Pin (cut or remove the wire going back to the main board of course).
There are circuits on the inverter board to detect if one of the lamp is not connetced, of once the lamp is fired up with starting voltage but fail to stay on, or the lamp draw too much current, that will cause the inverter to go into shutdown protection mode, so it will only take one bad lamp to be bad to shut down the circuit. This detection happens in the first 3 seconds if something is not right in 3 seconds, it will go into shutdown.

Cool!

I'm gonna try it then.

Thanx as usual, BudM!!

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Didn't work. Nada, zip, caput. I tried tying both inverter board "ON/OFF" together and triggered them with a 3V source and with the ERROR lines clipped and not a peep. I then pulled the ribbon cables that connect the master and slave boards and tried it again. Same result. I pulled the ribbon cable from the T-con to the master inverter board....same result.
It should have done something I figured at this point. Not a damn thing! I have good +24 and GND's at each board.
Now I am just unsure at this point what is up. I will end up pulling it all apart and check all 20 tubes by hand and if those are all good I am pretty much stuck.
If I cannot find something obvious at that point then it is off to its intended original destination....back in the dumpster!
By the time I end up throwing boards and lamps to this thing I could just have well saved my coin towards a new one!

I generally don't concede to defeat but the aggrivation isn't worth the effort.
Thanx again to all who have helped!
I'm leaving these things in the future in the hands of the more capable than I.

-Bud

[selldoor]

Re: Need Some Repair Advice LG 47LG50

I tried tying both inverter board "ON/OFF" together and triggered them with a 3V source

What does that mean exactly?

What you are supposed to do is cut the blon wire from the main board (in such a way that it can be resoldered then plug the socket back in to the power supply so you have the other pins connected then you connect a 3 volt battery negative to the chassis ground on the set and positive to the blon pin on the power supply.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Hi, selldoor,
I can elaborate a bit further. I snipped the "ON/OFF" wire at the cable connector coming from the header on the PSU down to the master inverter board and I snipped the wire from the "ERROR" terminal as well to preven it from sending any erroneous shutdown signal back through (this was my thinking anyway). I pushed the on button and waited until the TV was fully booted (dimly glowing blue LED in the front panel) and the SMD mounted green status LED was illuminated solid on the main board. There was 24VDC going to the inverter and slave boards at this time. I then added an external 3VDC source to the snipped and stripped wire leading DOWN to the master inverter board. Nothing happened. I then snipped the OTHER wire going to the "ON/OFF" terminal leading to the slave in hopes that maybe that needed the same, simultaneous voltage signal. Again nothing. Interestingly, the silkscreened nomenclature of both boards' pinouts do not match when I trace down each individual wire. For instance, the wire on the "ON/OFF" header at the PSU goes directly to the terminal marked "ERROR" on the master inverter board. This is what is even more confusing
I then tried it again this time after pulling the ribbon cables that join the two inverter boards. Same scenario. Okay, I then pulled the small ribbon cable that goes from the master to the T-con. Same end result.

My thinking, (which I'm certain is skewed at this point) is that if the DC voltage is present at the inverter board(s) and you then apply the start signal, in this case the "ON/OFF", should it not start the oscillator circuitry and fire the XFRMR's primary side with the correct 24VAC at the corrected Hz level and thusly fire the bulbs?

It seems pretty elementary and I was hoping that all of the complicated "shut down" circuity was truncated at the board by eliminating the error signal that runs through the PSU and back into the main CPU which then, in turn, would send the TV in error mode.
Am I coorect in thinkin or am I all F'ed up here?

Thanx!

Bud

[selldoor]

Re: Need Some Repair Advice LG 47LG50

I am sorry I am sure it makes sense to you but I just cant follow it.
Initially you said you ere just going to cut the blon wire and feed 3v to it instead.
Budm said OK and I thought yes ok but then you have done something entirely different that I have never heard of anyone doing before. Budm has already said the error status need dropping from 3v - probably to less than 1v so feeding 3v to it (if that is what you did makes no sense (to me)
Wait for another opinion by allmeans but I suggest you heal all the wounds and try what you initially said following what I said in post 32 I have seen that work many times before.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Okay, I did exactly as you said to the letter and still nothing. I used a new 3.2V button cell battery. Got a good 3.2V to the ON/OFF terminal and fired up the set. After it was good and booted I checked the voltages back at the header on the PSU. The only voltage I am getting now is just the 3.2 that was being fed by the battery. I shut it off, pulled the plug and took the battery off. Fired it up and it is devoid of ANY control voltages now. Just the +24 at the 5 pinouts along with the 5 GND. Now I guess something is awry within the main control board which, was my first suspicion, for the fact I initially had no pic, no sound and no backlighting.

I think this set is hosed. So many components on the main board I am just going to pitch it and buy another good used board. Guess Ill keep going until I find the culprit. Still seems odd, however, that I cannot "tickle" the inverters to get some fire to the tubes.

I will inspect all of the tubes in the mean time.

Thanx!

Bud

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Update:

I pulled all of the CCFL's and they all test good.

Time to start throwing boards at this thing I guess. I'll start with the main board since this seems to be the origin of the initial problem.

Thanx again to all!

Bud

[selldoor]

Re: Need Some Repair Advice LG 47LG50

You need to be careful in matching the board exactly with the old one.
If is is a pull I think it should be out of a set with the same make and preferable same size panel. Tell the vendor what its needed for and ask them if it is suitable. Try and get it on work or return basis.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Okay, guys...here's an update on this PITA TV.

I got another main board and plugged it in and, Viola! everything came on. That's the good news...of course it has to be followed by the bad news, right?

The picture is so bright that I can barely see anything displayed on the screen. All of the remote functions work as do the side buttons. I can go through the menu functions and I can make adjustments. I went into the picture sub menu and set the backlighting all the way to zero and while the screen did dim quite a bit the images were barely visible.
All of the audio and everything elseis fine except the picture is just a big fluorescent lamp.

Now what?


Thanx,
Bud

[budm]

Re: Need Some Repair Advice LG 47LG50

The pictures look washed out? Can we see the screen shot? It sounds like the GAMMA Voltages are not right, it is either the new main board needs to be setup or something in the T-CON Gamma voltage problem.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

Okay...

I attached the screen shots. I took some voltage readings on the header at the PSU that goes to the master inverter cable. I took two consecutive readings. One at 100% backlight and the other at 0%

100% readings:

BR1 = 1.739V
ON/OFF = 3.412V
PWM DIM = 5.09V
ERROR = 3.287V

and at 0%:


BR1 = 1.736V
ON/OFF = .847V
PWM DIM = 5.05V
ERROR = 3.285V

Interesting swing on the ON/OFF voltage

I got a board from a (he seemed anyway) knowledgeable TV guy and he said it *should* work. My board had a different suffix number than the one he supplied me even though they look identical with the exact same chipset and from the same model of TV. Maybe this is the issue?
My original board is an EAX42405502(5) and the one I received is an EAX4205502(11).
I have included pics of the orig. and the replacement.

Thanx again for the help! I am getting closer *fingers tightly crossed*

Bud