Need Some Repair Advice LG 47LG50

[69sixpackbee]

T-Con Voltage Measurments

I took some reading off of the T-con with my DVD player that was playing a movie and I got the following readings in no particular order:


Gamma
1-9 ~.32V
10-16 .75V
17 .3V
18 0V

SDA 3.2 V
VIN 12.3 V
SCL 3.27 V
TST PGM 0 V
POL 1.62 V
ASTH .003 V
ATP1 .2 V
SIN2 1.63 V
A_STHR .001 V
B_STHR .006 V
VST .4 V
VGL -5 .56 V
VDD 3.2 V
VCOM 5.36V
VGH 17.49 V
VGHP 19.68 V
V33V 3.23 V
V12V 12.3 V
V506V 5.42 V
Pin 192 0 V
DRL1 3.2 V
0E1 . 87 V
STV .003 V
CKV 1.82 V
VSCM 5.35V

From what I was gathering in like postings this looks like a bad T-con, yes?

Thanx again for the help!

Bud

[aaronwt6]

Re: Need Some Repair Advice LG 47LG50

Yeah. Looks bad to me.

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

That's what I thought.
Thanx!

[69sixpackbee]

Re: Need Some Repair Advice LG 47LG50

It's alive!!! Got the new T-con board and that was it. I had to replace the main board and the T-con both. Thanx again to all of the knowledgeable folks who lent a hand from this great forum!

BTW, I took a chance and got a replacement main board that although was for the exact same model set, the part number was slightly different and it works just fine my main board was an EAX42405502(5) and I put in one with the same # but with a suffix number (11) and it works just peachy.
For a $75.00 investment I've got a pretty nice 47-incher!

Thanx again,
Bud

[dead66]

Re: Need Some Repair Advice LG 47LG50

OK, TV unplugged, then disconnect the white flat ribbon cable between the T-CON and the MASTER INVERTER board (left board), then power up the TV to see if the backlights will come on.

Hi,I have the same TV with no back lights, just a quick flash when power on. If I remove the white ribbon from the tcon to the master the back lights come on and all light up with no flickering. Would this mean the bulbs are arcing or do I have a board problem? I am new to repairing tvs but have fixed several for friends with bad caps or shorted mosfets, but this is the first one I have run into where there is no visible damage and the boards all look good. Hoping you could point me I the right direction to start trouble shooting. I am good at small component replacement and soldering, so if it is a board problem I would take a shot at repairing instead of replacing, but I have not been able to locate the problem, making me think I may have a carbon tracking and arcing problem with the bulbs or a weak transformer triggering the shutdown of the back lights. My plan is to test all the transformers next, but wanted to see if someone with knowledge could explain what maybe happening with this one, before I go barking up the wrong tree. Thanks, new to the forum, and I fix things for friends and neighbours as a hobby as I enjoy trying figure out how things work, and how to solve problems.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Hey Guys I picked up one of these sets today, with no backlight. A quick assessment says the trouble is in the inverters or tcon, I found this thread and pulled the ribbon between the master and tcon as Budm suggested and I get good backlights as the above poster did. Ive gone though the master inverter and the transformers ohm test ok, fuses intact. Im curious what the ribbon does, it has 2 lines that say dim, and all the centers are ground. It is curious that it lights fine without that ribbon.
Caleb

[budm]

Re: Need Some Repair Advice LG 47LG50

The T-CON control the backlights level based on the scene of the video so they can claim the TV has high contrast ratio which is not real.
I would use without that function, it is bad when you watch movie that has dark seen like space scene, it gets way too dark and cannot see any star in the back ground and if the scene changes a lots from bright scene to dark it looks like the screen is flickering. Leave that out if you can do without it.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Ok well if that is the case I have something else wrong as well, with it unhooked it turns on with backlight but still doesnt show menus, tcon has 12v on both sides of fuse, as well as 3.3 leaving the reg. However gamma test points show no voltages at all. I would be fairly certain the tcon is shot, but am getting no sound after hitting the input several times. Will try hooking up a source to see if it has auto mute.

[budm]

Re: Need Some Repair Advice LG 47LG50

Yes, does sounds like bad T-CON which also explains why you do not have backlights due to the control signal from the T-CON is forcing off the BL line.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Shopjimmy is out of stock but I found one pretty cheap on ebay, hopefully it isnt hosed. Will order it up and let you all know how it works.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Well, got the "new" tcon in and have the exact same symptoms, with the jumper to the inverter pulled it comes on with backlights, have 12v and 3.3v present on the tcon, but no attempt at display. No voltages on the gamma test points on this one either. Pulled the main and looked it over, didnt find anything obvious. found what appear to be 3 voltage reg on the back side of the board, will be testing them out next. any other ideas, this main appears to be pretty rare, found some other size versions of it I might be able to swap out the eeprom.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Tested out all the vregs on the main and all were within spec, finally got it to output sound after messing around with the input button a bunch.... back to the tcon.

I found a mosfet with 12v on one side and nada on the other, bypassed with a 1n4148 to see if I got a display and what do ya know I got lines. So some progress, mosfet is a spp9435. It has 12v on the gate, is it safe just to bypass it with a jumper for testing purposes? I used the diode as a safety measure, but I'm sure the mosfet has much less voltage drop and thought maybe that's why I was getting lines on the display? What do you think? Tagged mosfet in picture below

[budm]

Re: Need Some Repair Advice LG 47LG50

It is P-CH MOSFET, so the Gate must be at least 3V less than the Source pin for it to be on.
You can force on by connecting the Gate pin to ground through 500~1K resistor.
It is not getting the ON command from one of the ICs on the board.
There are many Voltage test points on the board also, for I.E.
VD33V (3.3V), VGL, VCOM, VGH, etc.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Learned something new today, didnt know that about P channel fets -thanks for that Bud. soldered a 330k resistor from gate to ground and now have the same lines I had with the ebay tcon. Im not sure whether this means I have trouble beyond the tcon or if they are just both bad.
Tried rocking out lvds connector and the lines move.

[budm]

Re: Need Some Repair Advice LG 47LG50

Do you mean 330 Ohms? Do you get 12V now on the Drain pin?
I would say you have bad T-CON.

[Caleb]

Re: Need Some Repair Advice LG 47LG50

It actually was a 330k, was the first one I found. and yes it does turn on the fet. Interestingly enough I have a Toshiba that ceased working again, I opened it today to find it uses the same tcon, after fixing an open resistor on the power board I swapped out the original tcon from the LG into the Toshiba and it works just fine. I put the known good tcon into the lg and it still has same issue.

So my next question, does the lvds cable usually have any switching info from the main? I thought it was just power, gnd and video signals.

[budm]

Re: Need Some Repair Advice LG 47LG50

If you can get the spec sheet of the panel, it will have pin out of the T-CON board.
Can you locate the sticker on the panel?

[Caleb]

Re: Need Some Repair Advice LG 47LG50

Here's a picture of the sticker

[budm]

Re: Need Some Repair Advice LG 47LG50

Well I am running of idea, I looked at the spec sheet and it does not seem to have control signal pins.
New main board?

[Caleb]

Re: Need Some Repair Advice LG 47LG50

I was thinking it was likely a scan driver failure, I am seeing main board sending out lvds voltages, cant really test them without a good panel though. If i unhook the left ribbon to the panel I get half white half lines, if I unhook the right ribbon I get half black and half lines. I guess I will have to take a look at the panel drivers to see if there is anything amiss.

pulled the top cover and dont see any scorching or burnt ics, since this has the same tcon as the toshiba if I lined them up back to back would it be safe to tie in the lvds from toshiba to the lg? that should tell me if the panel is ok or not.