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Old 07-27-2018, 05:27 PM   #1
mtskibum16
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Default LG 55LW5600 No Video No Sound

I'll start by saying I'm not much of a techy, but my TV is dead and thought I'd pull the thread of repairing it. So keep in mind my electronics knowledge is very limited.

I've spent the last few days reading threads and doing research on what might be wrong with my TV. I did try a reflow (both heat gun and oven) of the main board based on a number of people with similar symptoms with no change.

So there is no "standby light" on when the TV is just plugged in but off. I believe there used to be but I can't be 100% sure. When I turn the TV on (touch panel or remote) I get a "click", the power indicator lights up red, fades off, lights up red again, fades off, then lights up blue/white and stays on. No screen flashes and I can't see any signs of an image with a flashlight in a dark room. I get a "click" when I turn it off.

I have a multimeter and checked P201 (power out from power board to main board) while the TV was on.

L Column/R Column/Voltage(measured)
N.C./Error
12v/PWM/~12v
12v/N.C./~12v
12v/DRV-ON/~12v
GRD/VSYNC_IN
GRD/GRD
3.5v/3.5v/~3.5v
3.5v/3.5v/~3.5v
GRD/GRD
GRD/GRD
24v/24v/~24v
Power-On/24v/~3.3v

Rather than hope that my symptoms where "close enough" to others and keep tinkering, I was hoping to get advice from the experts here. Any help is appreciated. I'll add pictures in a bit.
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Old 07-28-2018, 09:03 AM   #2
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Default Re: LG 55LW5600 No Video No Sound

Can you post pictures of your boards and voltage measurements are easier to read if posted similar to the following.
Without the set in front of us, the more information you can provide the better chance of finding a solution.
Attached Images
File Type: jpg PJ90 Readings.JPG (50.6 KB, 24 views)
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Old 07-28-2018, 02:08 PM   #3
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Default Re: LG 55LW5600 No Video No Sound

Quote:
Originally Posted by dick_barton View Post
Can you post pictures of your boards and voltage measurements are easier to read if posted similar to the following.
Without the set in front of us, the more information you can provide the better chance of finding a solution.
I have attached some pictures of the set. In your example, are those readings on each end of the ribbon or what? I was a bit confused on what the tho columns meant. At any rate, the only that jumped out as odd to me was the last one. Labeled as 24v and I measured 3.3v.
Attached Images
File Type: jpg _SAM0170.jpg (531.8 KB, 18 views)
File Type: jpg _SAM0171.jpg (553.8 KB, 21 views)
File Type: jpg _SAM0172.jpg (553.0 KB, 18 views)
File Type: jpg _SAM0173.jpg (348.4 KB, 9 views)

Last edited by mtskibum16; 07-28-2018 at 02:13 PM..
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Old 07-28-2018, 03:08 PM   #4
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Default Re: LG 55LW5600 No Video No Sound

The connector on the power supply board that goes to the main board has 24 pins.
The exposed pins you can see from the top side of the board are the ODD number pin, if you look at the board you will see Black Triangle marking which indicates pin1 of the connector.
To get to the EVEN number pins you have to use the skinny probes to probe the pins from the wire entrance side of the connector.
L Column (ODD). R Column (EVEN)
pin 23: N.C. pin 24: Error
pin 21: 12v. pin 22: PWM (Dimming)
pin 19: 12v. pin 20: N.C. (No Connection)
pin 17: 12v. pin 18: DRV-ON (same as BL-ON)
pin 15: GRD. pin 16: VSYNC_IN
pin 13: GRD. pin 14: GRD
pin 11: 3.5v. pin 12: 3.5v
pin 9: 3.5v. pin 10: 3.5v
pin 7: GRD. pin 8: GRD
pin 5: GRD. pin 6: GRD
pin 3: 24v. pin 4: 24v
pin 1: Power-On. pin 2: 24v
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Last edited by budm; 07-28-2018 at 03:10 PM..
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Old 07-28-2018, 03:46 PM   #5
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Default Re: LG 55LW5600 No Video No Sound

Quote:
Originally Posted by budm View Post
The connector on the power supply board that goes to the main board has 24 pins.
The exposed pins you can see from the top side of the board are the ODD number pin, if you look at the board you will see Black Triangle marking which indicates pin1 of the connector.
To get to the EVEN number pins you have to use the skinny probes to probe the pins from the wire entrance side of the connector.
L Column (ODD). R Column (EVEN)
pin 23: N.C. pin 24: Error
pin 21: 12v. pin 22: PWM (Dimming)
pin 19: 12v. pin 20: N.C. (No Connection)
pin 17: 12v. pin 18: DRV-ON (same as BL-ON)
pin 15: GRD. pin 16: VSYNC_IN
pin 13: GRD. pin 14: GRD
pin 11: 3.5v. pin 12: 3.5v
pin 9: 3.5v. pin 10: 3.5v
pin 7: GRD. pin 8: GRD
pin 5: GRD. pin 6: GRD
pin 3: 24v. pin 4: 24v
pin 1: Power-On. pin 2: 24v
Thank you for the info! SO on the wire entrance side, there are two rows of wires (so 24 total). Are the even pins the top or bottom row of wires? I hope that makes sense.
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Old 07-28-2018, 04:08 PM   #6
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Default Re: LG 55LW5600 No Video No Sound

Bottom.
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Old 07-28-2018, 04:59 PM   #7
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Default Re: LG 55LW5600 No Video No Sound

Quote:
Originally Posted by budm View Post
Bottom.
Quote:
Originally Posted by dick_barton View Post
Can you post pictures of your boards and voltage measurements are easier to read if posted similar to the following.
Without the set in front of us, the more information you can provide the better chance of finding a solution.
This is the connector discussed above. Hopefully that means something to you guys.
Attached Images
File Type: png Screen Shot 2018-07-28 at 3.55.47 PM.png (23.0 KB, 20 views)
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Old 07-29-2018, 04:32 AM   #8
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Default Re: LG 55LW5600 No Video No Sound

DRV_ON is missing which I believe turn the backlights on and is controlled by the main board.
On some sets if you disconnect the main board from the power supply and switch on, the backlights come on and stay on?
Are you certain you have no picture. Keep pressing the menu button on the remote and check the screen carefully.
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Old 07-29-2018, 10:14 AM   #9
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Default Re: LG 55LW5600 No Video No Sound

I don't see the screen. Just got the room nice and dark and inspected again with a flashlight. I don't see anything.

I tried unplugging the main board and the TV doesn't turn on. I read somewhere about jumping certain pins (maybe with a resistor?) to get the backlights to come on.

So what is the most logical way to diagnose this? Is the no standby light and or the blinking red light in startup any indication of anything?
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Old 07-29-2018, 10:44 AM   #10
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Default Re: LG 55LW5600 No Video No Sound

You could try disconnecting the main board from the power supply and connect any of the 3.5V pins to DRV_ON pin at the power supply end using a 1K resistor and see if backlights come on and stay on.

You may also have to connect 3.5V to Power_On pin if the 12V & 24V are not present using a second 1K resistor.

Last edited by dick_barton; 07-29-2018 at 10:47 AM..
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Old 07-29-2018, 10:54 AM   #11
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Default Re: LG 55LW5600 No Video No Sound

Have a read through this. Troubleshooting Page 53 onwards
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File Type: pdf LG_55LW5600_Training.pdf (12.55 MB, 38 views)

Last edited by dick_barton; 07-29-2018 at 10:57 AM..
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Old 07-29-2018, 11:25 AM   #12
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Default Re: LG 55LW5600 No Video No Sound

Ok I'll try that and read through the info. There are two connectors going from the power board to main board. Do I disconnect both or only the connection P201 I posted?

Last edited by mtskibum16; 07-29-2018 at 11:30 AM..
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Old 07-29-2018, 11:41 AM   #13
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Default Re: LG 55LW5600 No Video No Sound

Ok, I jumped DVR-ON to 3.5v and Power-On to 3.5v. Plug the TV in to the wall and the back lights come on and stay on.
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Old 07-29-2018, 12:39 PM   #14
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Default Re: LG 55LW5600 No Video No Sound

It does look as though you have a mainboard fault with DRV_ON not switching. Can you post photo's of your main board.
Check the voltages on Q504 on the mainboard (Page 76)

Last edited by dick_barton; 07-29-2018 at 12:43 PM..
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Old 07-29-2018, 12:43 PM   #15
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Default Re: LG 55LW5600 No Video No Sound

Quote:
Originally Posted by dick_barton View Post
It does look as though you have a mainboard fault with DRV_ON not switching. Can you post photo's of your main board.
Picture of the mainboard is pic 3 in post 3. I can get better pics of anything specific. Also page 71 of the link you posted has details on it. I'm working on reading through that.

I have attached the readings for Q504 with the TV off and TV on.
Attached Images
File Type: png Screen Shot 2018-07-29 at 12.24.09 PM.png (15.8 KB, 15 views)

Last edited by mtskibum16; 07-29-2018 at 01:26 PM..
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Old 07-29-2018, 03:14 PM   #16
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Default Re: LG 55LW5600 No Video No Sound

+3.3V_ Normal appears to be missing. Can you check what voltage is on pins 2, 6, 7 & 8 of IC505 (Page 73)
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Old 07-29-2018, 10:23 PM   #17
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Default Re: LG 55LW5600 No Video No Sound

This is assuming counter clockwise around the component from pin 1 marked with the dot on page 74.
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Old 07-30-2018, 03:36 AM   #18
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Default Re: LG 55LW5600 No Video No Sound

Quote:
Originally Posted by mtskibum16 View Post
This is assuming counter clockwise around the component from pin 1 marked with the dot on page 74.
Yes that is correct. It looks as either the IC has failed and is not giving out the +3.3V_Normal required to drive the backlights on via DRV_ON or since
this supply goes to many other parts of the circuit as shown on Page 104, one part may be pulling this supply low.

With the set powered off can you measure the resistance in ohms of IC505 pin 8 (+3.35V OUT) to pin 1 (GND)

What is the part number written on top of the IC505
Attached Images
File Type: jpg IC505.JPG (37.6 KB, 16 views)
File Type: png Measured IC505.png (31.8 KB, 13 views)

Last edited by dick_barton; 07-30-2018 at 03:48 AM..
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Old 07-30-2018, 07:16 PM   #19
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Default Re: LG 55LW5600 No Video No Sound

Plugged in (but off): 162.5 ohms
Not plugged in: 12.3 ohms

I'll have to bring an inspection glass home from work tomorrow for the part number. I can't make it out with the naked eye. My wife thinks it's as follows, but I'll verify tomorrow.

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Old 07-30-2018, 08:45 PM   #20
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Default Re: LG 55LW5600 No Video No Sound

Quote:
Originally Posted by mtskibum16 View Post
Plugged in (but off): 162.5 ohms
Not plugged in: 12.3 ohms

I'll have to bring an inspection glass home from work tomorrow for the part number. I can't make it out with the naked eye. My wife thinks it's as follows, but I'll verify tomorrow.

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Is it 12 Ohms readings in both directions of the probes?
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