LG 39LN5700, TV shuts off immediately after being turned on, no picture

[pgram]

I was originally planning on scrapping the TV, but as I am without a descent TV at the moment and I figured I would give it another look.

The situation: When testing voltages on the 18 pin cable connecting the power supply to the main board I accidentally shorted 2 pins. Before the TV would turn on, but there was no picture (the LED back light burnt out), after shorting the pins the TV won't even turn on (its red LED that indicated it off just flashes off then on again when the TV is power button is pressed.

Is it still worth repairing or was I right with my original assessment to just scrap it? The TV has had steady use over a 2-4 year time period, it was left on at least 2-4 hours a day.

[budm]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

Hard to help without seeing the whole back side of the TV so we can see all the boards and how they are connected together and the pictures of the connector you shorted together.

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

I shorted leads on the backside of the power supply board at the 18 pin cable (that connects the power supply board to the main board). I was (stupidly) trying to check voltages at the cable connector pins on the backside of the power supply board while the TV was plugged in. I'm not entirely sure what was shorted as my view was obscured.

These are the voltage readings I am getting now at the 18 pin cable (TV plugged in & powered off with cable to the LED backlight disconnected). This is on the topside of power board, from top to bottom:

1: -
2: 0.2
3: 0.2
4: -
5: 23.6
6: -
7: 3.46
8: 3.46
9: 3.35


Pictures:

I highlighted the cable in the first picture and drew a read arrow to the area that where my multimeter lead caused the short. Let me know if you need pictures of anything else.

[dick_barton]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

The connector has 18 pins. With the power supply disconnected from the main board can you put the voltages read alongside the Pin 1 -> Pin 18

Edit
Some of the solder joints are not looking to good.

[budm]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

http://www.shopjimmy.com/catalogsear...?q=LG+39LN5700

OK, the connector P201 on the power supply board has a chart to tell you what each pin is for, we need you to list the pin number, pin name, and the DCV reading when the TV is NOT turned on yet and AFter the power switch is activated.
You have ODD pin that you can get access from the top of the board, the even pins can get access using small probe poking into the socket back side.
DCV readings examples:

Pin 1, PWR-ON = ??? V (TV OFF), ????V (TV ON)
Pin 3, 3.5V = ??? V (TV OFF), ????V (TV ON)

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

The connector has 18 pins. With the power supply disconnected from the main board can you put the voltages read alongside the Pin 1 -> Pin 18

Edit
Some of the solder joints are not looking to good.

Power Supply voltages at the 18 pin connector when disconnected from the main board:

17 (GND) 0
15 (12V) 0
13 (12V) 0
11 (GND) 0
09 (24V) 0
07 (GND) 0
05 (3.5) 3.45
03 (3.5) 3.45
01 (PWR-ON) 0

18 (GND) 0
16 (N.C) 0
14 (12V) 0
12 (GND) 0
10 (24V) 0
08 (GND) 0
06 (N.C) 0
04 (PDIM) 0
02 (DRV-ON) 0

The solder joints on the back of the Power Supply do look a little rough. I had originally started removing components to keep as a backup when I planned to scrap the TV, but resoldered them back on after I decided to give the TV a second go. The Weller iron I used has seen better days (I have a newer iron, but it wasn't getting hot enough to melt the solder consistently).

OK, the connector P201 on the power supply board has a chart to tell you what each pin is for, we need you to list the pin number, pin name, and the DCV reading when the TV is NOT turned on yet and AFter the power switch is activated.
You have ODD pin that you can get access from the top of the board, the even pins can get access using small probe poking into the socket back side.
DCV readings examples:

Pin 1, PWR-ON = ??? V (TV OFF), ????V (TV ON)
Pin 3, 3.5V = ??? V (TV OFF), ????V (TV ON)

These were the voltages on the odd pins:

1st reading : voltage change after power button pushed

17 (GND) 0
15 (12V) 1.7 : 3.1 > 1.2 > 1.7
13 (12V) 1.7 : 3.1 > 1.1 > 1.7
11 (GND) 0
09 (24V) 23.7 : 23.1 > 23.7 > 0 > 23.7
07 (GND) 0
05 (3.5) 3.4 : 3.3 > 3.4
03 (3.5) 3.4 : 3.3 > 3.4
01 (PWR-ON) 3.3 : 0 > 3.3

More pictures:

• Close up of the back of the Power Board near the 18 pin connector
• Close up of the front of the Power Board near the 18 pin connector
• Close up of the front of the Main Board near the 18 pin connector

[budm]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

It looks like the switched 12Vdc circuit is damaged.
Need to do board tracing next to see how switched 12V is generated.
Pictures provided by shopjimmy.

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

It looks like the switched 12Vdc circuit is damaged.
Need to do board tracing next to see how switched 12V is generated.
Pictures provided by shopjimmy.

Thanks for the pictures, this helps me out a lot. I didn't get a good picture of the back of my Power Supply Board before I started removing components.

To start with the obvious issues, it looks like I may have made a mistake in two places when resoldering components.

I've made 4 comparison shots with the shopjimmy board on top and mine on bottom. The first two pictures look like they could be an issue, not sure about the latter two. In the last picture, the orientation of the blue thingy on the left and the 3 resistors in the center are reversed (although I believe the orientation of the stuff on my board in this photo is the same as what it was when I removed the board).

I'll keep looking to see if there's anything else that I may have messed up.

[dick_barton]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

Hello pgram,
You are in desperate need of a new soldering iron or tip for it. since you really need to finish off those joints tidily or they will cause you more problems than you started with.
Can you check D208 on the underside of the board by the connector. Is R226 missing off the board?

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

Hello pgram,
You are in desperate need of a new soldering iron or tip for it. since you really need to finish off those joints tidily or they will cause you more problems than you started with.
Can you check D208 on the underside of the board by the connector. Is R226 missing off the board?

I'm not sure I have a replacement tip handy for my Weller soldering iron. I've been looking for one for a while and have not had any luck, none of the local electronics stores had any in stock when I went looking for parts a month or so ago. I do have another iron, but I haven't had a lot of luck with it so far. I might try changing the tip on it.

I don't think R226 was ever on the board, it's not shown on the replacement at shopjimmy that budm just linked to. What is the issue with C210 and D208? I'm not seeing any major differences from other nearby connectors and I didn't touch either with the soldering iron.

[dick_barton]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

The 12V supply is missing so you need to start to check components and although I'm not 100% certain I think D208 is a diode in line with the 12V supply. It wouldn't hurt to check all your diodes and zener diodes in that area.

C210 looks as though its got a solder blob stuck on it which can be wiped off.

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

I checked all the diodes I could find nearby and I didn't find any that failed open circuit (didn't remove them from circuit though). Scratching my head on what to check next, I haven't been able to find a service manual / schematic for the TV. I found a service manual for the Asian market model at a similar size, but it had different layout in the schematic.

These are the readings from I got with my multimeter in diode mode:

Front of PCB:

D101  1 , 492
D105  1 , 492
D203  185 , 1500+
D205  185 , 1500+
F100  0 , 0
R222  601 , 1240
ZD102 1 , 682
ZD102 511 , 1
ZD103 716 , 1
ZD105 1 , 710
ZD202 618 , 1

Back of PCB

D206  690 , 182
D207  1183 , 609
D202  609 , 1
ZD203 0 , 709

Voltages readings (18 pin cable to main PCB disconnected):

450v 68uF capacitors (across legs)
 EL9 to C111: 167.6v 
 EL10 to C110: 167.6v
 EL51 to C109: 167.7v
C209: 3.4v
C222: 0v
IC202: 23.5v (at pin 2 / V-in)
P203 0
P202 0
P802 1.54
F100 (fuse) 0 on both sides (something seems off...)

Voltages readings (18 pin cable to main PCB connected):

P202 0.182
P802 0.113
LED+ 83 (P801?)
LED- 0.16 (P801?)

I found my original voltage readings from before I shorted the 18 pin connector as well. These readings make me wonder if the problem is really on the Power Supply board, the readings when the TV was powered off were almost the same:

93.2~118.5V output
Input listed as: 100-240~ 50/60Hz 2.0A
Output listed as: 133.2V - 0.37A 39 Inch

TV on:
LED+ connector: from 232V down to 214V (cycling voltage)
LED- connector: from 21V down to 15V (cycling voltage)
P801: from 232V down to 214V
P802: from 19.5V down to 16.8V

TV off:
LED+ connector: 81V
LED- connector: ?
P801: 82.2
P802: 0.36

At the 18 pin connector (P201):

Odd pins with TV on:
17 (GND)  0
15 (12V)  11.8
13 (12V)  11.8
11 (GND)  0
09 (24V)  22.7
07 (GND)  0
05 (3.5)  3.4
03 (3.5)  3.4
01 (PWR-ON) 3.3

Odd pins with TV off:
17 (GND)  0
15 (12V)  0
13 (12V)  0
11 (GND)  0
09 (24V)  0
07 (GND)  0
05 (3.5)  3.3
03 (3.5)  3.3
01 (PWR-ON) 0

Also, I attached some pictures I made for reference.

[budm]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

What do you use to create that x-ray version?

[budm]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

The 12V is generated by the buck converter 8-PIN DIP IC202 (and associated parts L201, D206), it takes the 24VDC input (looks like pin 2) and down converted to 12VDC.
We need the P/N of that IC.

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

What do you use to create that x-ray version?

I noticed the PCB was translucent, so I shined a lot of light on one side of the board and took a photo of the other side. Then I used GIMP (image editor) to flip the photo and overlay it onto the one from shopjimmy.com.

The 12V is generated by the buck converter 8-PIN DIP IC202 (and associated parts L201, D206), it takes the 24VDC input (looks like pin 2) and down converted to 12VDC.
We need the P/N of that IC.

IC202 P/N: NR891D (1-1-3 DC/DC Converter ICs NR887D/NR891D)

I wasn't able to find anything using the labeling on L201. I'm not sure what the label is on D206, maybe "B86 264P" (it's very difficult to read). I added P/Ns for the ICs, a rectifier, mosfets, and some other stuff to the second photo.

[thoma]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

http://televid-sib.ru/index.php?board=165.0

LG SMPS schematics Registration required!!

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

http://televid-sib.ru/index.php?board=165.0

LG SMPS schematics Registration required!!

Thanks for the link, unfortunately it doesn't look like they have anything for the TV's Power Supply (EAY62810401 / EAX64905301) or L201 (it's labeled with "13S-DD06 FL 121218 F"). A Google site search didn't give me anything useful.

At the same time, the Forum is post, ie Administration checks messages for compliance with these rules after their publication, in connection with what is possible when a particular message may be offensive, inappropriate content, and have parties agree to bear all risks associated with it. 9. Do not use in the name of various kinds of decoration themes (characters, intended only for visual highlight topics, but do not carry the semantic load)

In addition, it is forbidden: placing and discussion of materials of a pornographic nature, placing advertisements, discussion of politics and politicians.

Hard not to laugh reading this in the registration requirements when they have a big old Colorado down in the lower right hand corner, seems ridiculously contradictory.

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

http://televid-sib.ru/index.php?board=165.0

LG SMPS schematics Registration required!!

Actually I take back my earlier reply. I couldn't find the exact Power Supply Board schematic there, but I think I may have found one close enough to use as a guide. This one looks to have a lot of the same P/Ns (see attachment). Thanks for that link.

The screenshot was taken from the schematic for the "Power supply + LED drv LGP32-13PL1 EAX64905001 EAY62810301", I think it's this board.

[pgram]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

More measurements after looking at the schematic in my last post:

Voltage readings with TV plugged in, but powered off:

J44: 23.7v
C217: 4.7v
IC202 pin 7: 4.1v
R233 (both sides): 0v
L201 pin 1: 0.18v
L201 pin 8: 0.18v


Resistance measurements:

IC202 pin 4: 0 Ohms
L201 pin 5: 990 Ohms

I've attached an updated picture of the top of the Power Supply PCB with better labeling.

[budm]

Re: LG 39LN5700, TV shuts off immediately after being turned on, no picture

What resistance do you have between pin 3 and GND?