Re: Lg 55ga6400 trying to power on but turn off completely
I paid $119 plus shipping on eBay from seller "tvpartologist." Some of the regular TV parts shops had listings for less money (around $75) but were all out of stock.
John_Clark
Member
Last Activity: 08-23-2018, 01:30 PM
Joined: 08-18-2018
Location: Charlotte, NC
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Re: Lg 55ga6400 trying to power on but turn off completely
Replacement (eBay used/tested) main board installed and TV works.
Thanks again for all your help! I learned a ton from this thread so I really do appreciate it.
JohnLeave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Thanks to both of you! You have been a tremendous help and the documents Bud provided me were also extremely helpful. That TCON training document was great. I wish I'd seen it while I was looking for the power supply traces from the TCON fuse to the main board as it showed exactly where they are.
I will either get this main board fixed or replace it and will update here with the results when I get it done. It doesn't look like Nick has my main board on his list. Mine is an EAX64872104(1.0)
Also,...Last edited by John_Clark; 08-21-2018, 07:42 AM.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
That's what I was thinking, too. I'm just reading the TCON training document. Thank you for that--very helpful! On page 27 it talks about running the Panel Test. Would it be worthwhile for me to do that just to confirm I get a pattern on the screen? I think this is a 3D set so I'm not sure if it has that feature on the TCON or not...My TCON looks a bit more complicated than the one in the document.
I'm fine with buying a main board for this set but I really want to be right since it's not mine. I'm confident...Last edited by John_Clark; 08-20-2018, 10:37 PM.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
OK, I was able to turn on the Drain which does power up the TCON board but still no picture or sound. I do hear a click at the TCON board when I do that. I also plugged in the small connector at the LED driver board which causes the backlight to go out but when I turn on the Drain on that MOSFET to power up the TCON board the backlight comes on and stays on even after removing the 100 ohm resistor from the gate. I still have the DRV-ON and P-DIM depinned at P201.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
I've noticed something else about that cap (C2435) right below the transistor (Q2407) in my pic above that has me puzzled. I've checked it for a short just using my DVOM and it's not shorted but when I power up the TV it's showing 12.46V on right side, same as my 12V rail (expected) and 12.41V on the other side (not expected.) There's not another cap on the board with the same voltage on each side. They're all normal voltage on one side and 0V on the other. Is that normal or is it possible it's just a bad cap on the main...Last edited by John_Clark; 08-20-2018, 06:40 PM.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Yeah, I'm 50 and it's taking more than one pair of glasses to see these numbers and traces. Guess I really should buy a loop...but I digress...
I managed to trace it back to pins 48-51 on the white connector ribbon cable. I'm not too good with marking up photos but I gave it a good try. I'll explain what I'm seeing in attached pic.
I have traced back from pins 48-51 at the lower left of picture and found that it goes up to the transistor up toward the top of the picture. At that transistor there...Last edited by John_Clark; 08-20-2018, 03:29 PM.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Thank you! Sadly, eyesight is the first to go when you start to get older! I looked that board over more times than I can count and did not see the F101 plainly (though very small) written there. There is no power on either side of that fuse so as I suspected there is no voltage going to the TCON board. The fuse appears to be good and there is no short to ground on either side of the fuse....Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
I've looked all over the main board and can't find which wire should be the 12v output from the main board to the TCON board. It has to be on one of the ribbon cables but the terminals are so tiny I don't want go probing every one and possibly short something out.
I have probed all over the TCON board, mostly on each side of the larger surface mount caps and can find no voltage anywhere on the board. I cannot find a fuse anywhere on the TCON board, either. Would it be a good assumption that power is not making...Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Attached is a pic of the TCON board. I see lots of very small test points on it and I could certainly probe them with a scope but without some service info/diagrams how do I know what I'm looking for? How fast are these signals?
Also, I'm a little confused at the progress so far. Am I correct in assuming that my power supply is good, my display driver board is good, and my backlights are good, and that I am now just trying to determine if either the main board is bad or the TCON is bad, or both? With no DRV-ON...Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
I'm reading through your TV troubleshooting guide again (it always helps to read again after you learn more about the systems) and I'm getting the the very dark screen with no pics and no sound and almost like there is no backlight but the backlights are working.
Is that indicating a problem in the TCON board as well? (per #4 in the guide) I guess I better pull the cover on that board.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
All I have is the backlight. No picture and no sound.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Got it. So I still have the DRV-ON and P-DIM depinned at P201 (A-DIM is plugged back in but I think you mentioned it's probably not used and I get no voltage on it at any time.) As suggested, I unplugged the small cable from the TCON to the driver board and turned it on. I am now getting a backlight that comes on and stays on. Progress! Is this indicating just the failed main board? It's probably worth a new main board but I just don't want to take a chance of damaging a replacement main board. If I plug in either the DRV-ON...Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
The small board that appears to have the wiring leading into the display has a connector from the PS board to it and then has a 14 pin connector from the board into the display. That 14 pin connector has a red wire on each end at the #1 and #14 pins and then black in between. I've looked at the voltages on those. The red wires go to around 40V when initially turned on and then settle in at 24V. When turned off the voltages slowly drop to zero. The black wires go to 3.3V and stay there. Again, this is with the DRV-ON, P-DIM,...Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Yes, I get 4.35v on the P-DIM and DRV-ON but only when I depin the DRV-ON wire at P201 between the main board and PS board. If I simply unplug P201 it I lose the 12 and 24v power supplies as well having nothing on the P-DIM and DRV-ON.
Edit: A-DIM stays at 0v no matter what.Last edited by John_Clark; 08-19-2018, 11:02 PM.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
OK...where do I find the standby power output pin? I don't see one labeled that way. The PWR-ON pin is the only power pin I see. There are two 3.5v pins that are hot when plugged in. Are those the standby power you're referring to? I tried the same thing using those for power but still no backlight.
I also noticed that when I depinned the wire from the main board to the DRV-On pin at P201 on the PS board that the DRV-On pin on the power supply jumped up from 88mV to 4.35V. Is that significant?Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
That's kind of what I figured. I did the resistor jump testing you suggested at P201. I depinned the connector and put a 1K resistor from the PWR-ON to the DRV-ON (BL-ON) pin. No backlight. I then put a 1K from the PWR-ON to the P-DIM and still no backlight. So, unless I did it wrong (feel free to correct me) I think it's toast. I'm not replacing backlights and a main board.
Thanks for all the help! I do it just for the learning and I learned a fair amount from this so it's very much appreciated.Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
How likely is it that replacing the main board will fix it? Is there something else that could also be damaged that would take out a new main board if I replace it?Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
...thus why I guess I should have started a new thread. It's not the power supply board at all, right? I kind of suspected that when I found all the voltage rails good. Time for a new main board, I guess. Is there any way to determine what has failed on the main board? Finding diagrams of these boards is near impossible, though I did find a diagram of the power supply board on a russian forum yesterday.
Thanks,
John...Leave a comment:
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Re: Lg 55ga6400 trying to power on but turn off completely
Here are some photos of the TV and the boards.
Thanks!...Leave a comment:
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