Lg 47 led flashes then goes off

[deegee2016]

Hi all,

I have an LG47ODUE that shows LG Logo then goes black under torchlight image is visible.

Power supply board tests:

Standby voltages: in order on connector:

9) Ground - Ground = 0.0v
8) 12v - NC = 11.95v
7) 12v - 12v = 11.95v
6) Ground - Ground = 0.0v
5) 24v - 24v = 24.77v
4) Ground - Ground = 0.0v
3) 3.5v - PDIM2 = 3.54v
2) 3.5v - PDIM1 = 3.55v
1) PwrOn - DrvOn = 3.42v

Most voltages not present until standby button is pressed

Led Connector Tests:

106v down to 82.2v at led connector on both lines. LEDs connected

115v down to 82.2v at led connector on both lines. LEDs disconnected.

Diode Side Test: (red probe to cathode side and black to test points at led connector)

97v and decreases - cathode side of diode to test point at led connector.

LEDs have been checked out of the unit on a DC power supply two strips at 30v all LEDs work.

Work has been carried out previously as jumpers on led strips. Work fine out of unit on DCPS.

I had image but no backlight.

Could this be a caps issue???

Does the TV need all LEDs connected to work correctly (ie) cut out if not enough LEDs for load.

Obviously 88.2v is not enough to drive the leds



Anjy help will be most welcome

Regards Dee

[dick_barton]

Re: Lg 47 led flashes then goes off

Can't find any reference to LG470DUE. Are you sure it's the correct model number. Do you have any photo's of the circuit boards.
From the information provided it looks like you may well have led problems.

[budm]

Re: Lg 47 led flashes then goes off

82V is the feeding Voltage to the boost converter. We need good clear pictures of the whole back side of the TV showing all the boards and then good clear straight shot pictures of the top and the bottom side of the power supply board.
How many LED strips are there and total Qty. of the LED's?

LG47ODUE????

"Work has been carried out previously as jumpers on led strips. Work fine out of unit on DCPS.

I had image but no backlight.

Could this be a caps issue???

Does the TV need all LEDs connected to work correctly (ie) cut out if not enough LEDs for load."
What do you mean by jumpers on LED strips?

[deegee2016]

Re: Lg 47 led flashes then goes off

Thanks for the reply.

Its an LG 47" LED TV Panel model LC 470DUE(SFR-1)

Links to photos below.

https://ibb.co/eHwjuQ
https://ibb.co/j0BZuQ
https://ibb.co/dpMZuQ
https://ibb.co/i9oEuQ
https://ibb.co/eiWZuQ



My led install:
https://ibb.co/i9oEuQ

Previous repaired led install:
https://ibb.co/eiWZuQ

[deegee2016]

Re: Lg 47 led flashes then goes off

Hi again lads will sort requested info and get it up for viewing .

Led rows: 6 x two strips of 5 LEDs and 4 LEDs

Backlight strip: 94v -1331 47" Row 2.1 (Rev 0.7) R1-Type 6916L-1174A

Power supply: EAX64905501

AV Board: EAX647970031(1.2)

As stated there was previous work carried out which was not disclosed .

I have replaced approx 8-10 LEDs and all strips work fine on DCPS.

Also will only a few rows plugged in work or do they all need to be on for the load . ie too few and over voltage .
Thanks dee

[deegee2016]

Re: Lg 47 led flashes then goes off

Power Supply underside:


https://ibb.co/bv1UeQ
https://ibb.co/hoVpeQ

[dick_barton]

Re: Lg 47 led flashes then goes off

Schematic for the power supply.
http://electronicshelponline.blogspo...schematic.html

You need all the leds connected and working for backlights to come on.

If you are certain that all the leds are operating correctly then I would check the interconnections between led strips for continuity since this also tends to be a weak point.


Leds suitable for the panel available from
http://www.ebay.co.uk/itm/like/33200...1899735&crdt=0

[deegee2016]

Re: Lg 47 led flashes then goes off

Thankyou Mr Barton for the link .

So two or three only won't work it needs all connected and all LEDs functioning to stay illuminated.

I don't have steady voltage at led connector it should stay at 94v or thereabouts but it decreases.

Even with led connector pulled out .

[dick_barton]

Re: Lg 47 led flashes then goes off

Panel spec for backlights state 99.9V +/- 8.1V operating

http://www.panelook.com/LC470DUE-SFR...ter_20159.html

[budm]

Re: Lg 47 led flashes then goes off

'94V' printed on the strip is NOT the LED Voltage, that is the PCB compliance UL94V..

[budm]

Re: Lg 47 led flashes then goes off

'Led rows: 6 x two strips of 5 LEDs and 4 LEDs'
So 6 x 9 = 54 LED's, since you have TWO LED driver circuits that means each circuits drives 54/2 = 27 LED'S x 3V = 81V forward Voltage per each string of the LED.
81V forward Voltage + Vdrops of the PWM controlled MOSFET + Vdrops on the current sensing resistor which means the Boosted Voltage should be a little over 100V.
This is what you need to do:
1) LED connector is in place.
2) TV is off
3) Keep the meter black probe of the chassis.
4) Red probe on the LED connector pin 1 (LED -) then turn on the TV and see how high the DC V goes up to and wait 5 seconds to see how low it goes to, report the reading, turn the TV OFF.
5) Red probe on the LED connector pin 3 (LED +) then turn on the TV and see how high the DC V goes up to and wait 5 seconds to see how low it goes to, report the reading, turn the TV OFF.
6) Red probe on the LED connector pin 5 (LED -) then turn on the TV and see how high the DC V goes up to and wait 5 seconds to see how low it goes to, report the reading, turn the TV OFF.
7) Red probe on the LED connector pin 7 (LED +) then turn on the TV and see how high the DC V goes up to and wait 5 seconds to see how low it goes to, report the reading, turn the TV OFF.

Similar board;
https://www.badcaps.net/forum/showthread.php?t=64503

[deegee2016]

Re: Lg 47 led flashes then goes off

Thankyou Budm for your help with this. I usually work on iphones so this is quite new to me at the moment.

I will get the voltage output readings for you in a bit and post with board image with results.

I have one strip that's been jumpered that I need to rectify first and all strips should be good before the test.

Once again thankyou

[deegee2016]

Re: Lg 47 led flashes then goes off

Hi all,

Well I'm back with readings.

I have repaired the backlights and they stay on now.

Voltages are as follows:

Red probe to pin 1 led + = 105v high / 99.6v low

Red probe to pin 3 led + = 106v high / 104.8v low

Red probe to pin 5 led - = 27.7v

Red probe to pin 7 led - = 29.9v

Problem I'm having now is all I can see is white spot glows no image .

I must admit I may have put the difusser sheets back to front , I have kept them in correct order can this cause this issue?

Thanks again for help.....

[budm]

Re: Lg 47 led flashes then goes off

So what did you do to fix the backlights and make them staying on?

"Problem I'm having now is all I can see is white spot glows no image ." Please show us the screen shot of what you describe.

[deegee2016]

Re: Lg 47 led flashes then goes off

Thanks for replies, Well I replaced 35+ LEDs individually with my hot air station 10 secs at 280c airflow 40% .

I had the diffuser in front of the filters. I now have picture, sound with a little ghosting on 3 LEDs duevto lenses reflector spacers being removed on previous repair.

The picture is fine once the picture is on playing movie etc but when on menu you can see a few spots. Not cost effective to replace full array which is what I would have liked to do on this occasion.

Thanks again