Lg 47lv3700

[fcisolutions]

The LG 47LV3700 I'm fixing seems to power on but I have no backlight, no picture. Power supply has 3.3, 12v, 24v and 36v at the LED. I used a LED tester and seemed to get the LED's to light up but not sure if each strip is working. When I try to power the set, the red standby light on the front of the TV flashes 3 times and then turns blue. Not sure how to proceed.

Images are attached of the boards:

[Ahakim]

Re: Lg 47lv3700

What about sound? connect a video source (a demo for instance) and see..Most probably, leds (one or more) are sick!!

[fcisolutions]

Re: Lg 47lv3700

What do you mean by demo? I need to try each input as I have no idea what input the tv was set to when it went down.

[dskall]

Re: Lg 47lv3700

Press menu and with flashlight do you see anything on screen?

[fcisolutions]

Re: Lg 47lv3700

No ... I took my led tester and while lighting a strip of leds, can't see anything on the the lcd.

[dskall]

Re: Lg 47lv3700

You will need to post your voltages from connector on power board to mainboard with pin# pin id and voltage you get.

[dskall]

Re: Lg 47lv3700

Bad backlights on LG/Vizio are quite common, but you should get an image on screen. Also do you get a flash on the screen when you first turn it on?

[fcisolutions]

Re: Lg 47lv3700

I'm getting 120v dc at the bridge rectifier.

P201
Pin (dcv)
1 - 0
2 - 11.81
3 - 11.81
4 - 11.81
5 - 0
6 - 0
7 - 3.51
8 - 3.51
9 - 0
10 - 0
11 - 24
12 - 3.38

13 - 0
14 - 0
15 - 0
16 - 0
17 - 0
18 - 0
19 - 3.5
20 - 3.5
21 - 0
22 - 0
23 - 24.33
24 - 24.33

J35
Pin (dcv)
1 - 0
2 - 0
3 - 0
4 - 0
5 - 0
6 - 3.26
7 - 3.33
8 - 0

P202 & P203
36 volts with or without leds connected.

No flash when turning on. When I light the leds with the tester, no picture or menu or anything on the lcd.

[budm]

Re: Lg 47lv3700

"P202 & P203
36 volts with or without leds connected."
That does not mean much without knowing the pin names.
Which pin of the LED connector did you measure?
You have 16 strings of LED.
So how did you apply the LED tester to each string of the 16 LED strings?
If yo leave the black probe on the chassis and red probe on the P202 LED+ then turn the TV on, how high did the Voltage jump up to before it goes back down.

http://www.shopjimmy.com/lg-eay62169...pply-unit.htm#
LG EAY62169801 (EAX62865401/8) Power supply/LED driver.

[dskall]

Re: Lg 47lv3700

120vdc on bridge rectifier? What are you getting on your filter capacitor. + and - of 47uf caps. Three at bottom left. With tv powered on not in standby.

[fcisolutions]

Re: Lg 47lv3700

Thanks dskall & budm for your help!!

There are 2 - LED+ pins on each connector. I tested each strip of leds with the led tester by putting my red probe on the LED+ connector and the black lead on the 8 LED-'s on each connector. Each string of leds produced light.

The voltage on the LED+ connector with my black multimeter lead on chassis only gets to 36V without the leds plugged in and the same when I have the leds plugged in.

[budm]

Re: Lg 47lv3700

But did you try test I suggested?
'If yo leave the black probe on the chassis and red probe on the P202 LED+ then turn the TV on, how high did the Voltage jump up to before it goes back down."
The readings on other connectors are not helping much because we cannot tell if you have BL-ON signal or not. We need pin nmaes to go with each pin.
'I'm getting 120v dc at the bridge rectifier."
BTW, how did you measure that Voltage?

[fcisolutions]

Re: Lg 47lv3700

Yes ...

I wrote:
"The voltage on the LED+ connector with my black multimeter lead on chassis only gets to 36V without the leds plugged in and the same when I have the leds plugged in."

The voltage goes to 36 and stays there and doesn't move until I power the tv off. Am I missing something?

[budm]

Re: Lg 47lv3700

That means the Backlight LED driver circuit may not be getting the BL-ON signal from the main board to turn on the circuit so the Boost converter will run and provide boosted Voltage for the LED strings.
That is why we need the pin names to find out if BL-ON is present or not.
And the reason for leaving the probes on the test point before turning on the TV is to catch if the Voltage jumps up or not, if you put the probe on after the TV turn on, then you may not catch Voltage at start up.
BTW, when test LED string, if the one or more of the LED shorted out, the string will still light up, so unless the tester can show the total Vf of the LED string so you can compare the reading of each string and see if they read about the same or not, the Vf will be able to tell if you have bad string or not.
There is protection circuit in the LED driver, it will detect if one of the string has open circuit or short circuit and then it will shutdown, this happen very fast.

[fcisolutions]

Re: Lg 47lv3700

I'll never again NOT post pin names. Thanks budm. It looks the the DRV-ON is what we are looking for eh?

(a little joke... stay away from J35-Pin5 lol)

P201
Pin (dcv)
1:N.C - 0
2:12v - 11.81
3:12v - 11.81
4:12v - 11.81
5:GND - 0
6:GND - 0
7:3.5v - 3.51
8:3.5v - 3.51
9:GND - 0
10:GND - 0
11:24V - 24
12:PWR-ON - 3.38

13:ERROR - 0
14:PWM - 0
15:N.C. - 0
16RV-ON - 0
17:VSYNC - 0
18:GND - 0
19:3.5v - 3.5
20:3.5v - 3.5
21:GND - 0
22:GND - 0
23:24v - 24.33
24:24v - 24.33

J35
Pin (dcv)
1:Reverse - 0
2:N.C - 0
3:SCLK - 0
4:GND - 0
5:SIN - 0
6:SCL - 3.26
7:SDA - 3.33
8:VSYNC - 0

[budm]

Re: Lg 47lv3700

Yep, no BL-ON.
Can we see the whole backside of the TV? Is there a cable between T-CON board and the power supply board?

[fcisolutions]

Re: Lg 47lv3700

No cable from PS to TCON.

[syaoran123]

Re: Lg 47lv3700

Mainboard problem. Very common in LG LV##00 models.

Look up how to reflow the mainboard.

[fcisolutions]

Re: Lg 47lv3700

Tried baking the board today .... 385 for 8 minutes. Didn't power the tv but sure was filling for lunch lol.

[fcisolutions]

Re: Lg 47lv3700

I sent this board off to a repair service and got it back today. It's still doing the same.

I wanted to try and light the led's with the power supply using a jumper but wasn't sure whether this LG model needed a resister and also what voltage to supply.

Please help. Thanks