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I have an LED TV with sound but no picture. I did the

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flashlight test and i can...
I have an LED TV with sound but no picture. I did the flashlight test and i can see video.
Submitted: 2 years ago.Category: TV
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Answered in 3 minutes by:
9/19/2015
TV Technician: Anthony_Infotech, Technician replied 2 years ago
Anthony_Infotech
Anthony_Infotech, Technician
Category: TV
Satisfied Customers: 15,375
Experience: 20+ years experience TV expert (field and bench) 9 approved qualifications in TV-ELECTRONICS
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Hello

Welcome

The LEDs are supplied by the power-board and controlled by the main-board its usually the power-board that causes this however if you have a meter you could just check the positive and negative voltages out of the board to the LEDS this will be marked on the power-board or have you done that?

Anthony

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Customer reply replied 2 years ago
Hi Anthony. I did test the voltages coming off of P801, which is the connector that goes from the power supply to the panel. There are 2 LED+ pins and 2 LED- pins. The LED + pins at first power up jump to about 150V then settle at 80V. The LED- pins measure around 25V. In the schematic for the power supply, it shows the voltages and what they should be3.5V
(STBY)
3.325V ~ 3.675V
0.3W Under (15mA) - -
1.4A (0.2~1.4A) (ON condition) ± 5% 250 mVp_p
12V 11.4V ~ 12.6V 1.4A (0.2~1.4A) ± 5% 350 mVp_p
24V 22.8V ~ 25.2V 0.6A (0.1~0.6A) ± 5% 500 mVp_p
LED B+
93.2~118.5V 0.4A (0.380~0.420A)
± 5% -
93.2~118.5V 0.4A (0.380~0.420A)
TV Technician: Anthony_Infotech, Technician replied 2 years ago

I am not sure if the power-board is working correctly there, please disconnect the supply to the LEDs you should see a plug that can be pulled out either of the panel or on the power itself and check those + and - supplies again

Anthony

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Customer reply replied 2 years ago
Ok I made a mistake on the voltages I gave you so I did them again. This is what I get when the tv is turned on and I get the backlight flicker on and get the following: one of the LED+ voltage jumps to 160V then backlight turns off and voltage settles at 80V. The other LED+ pin goes to 105V when backlight flickers, then drops and settles at 80V. The LED- pins one jumps to 110V when backlight flickers and settles at 25v. The other LED- pin jumps to 44V when backlight flickers then settles at 22V. I hope this makes sense.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

so is that minus those voltages?so you will see a minus sign on the meter?

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Customer reply replied 2 years ago
I will get the voltages with connector removed
Customer reply replied 2 years ago
Ok with the connector removed, the voltage jumps to 170V on both LED+ pins then settles at 80V. Both LED- pins stay at around 0.6V.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

I think you may have to swap that power-board as it does not appear to be working properly, use the part-number etched on the board and try www.shopjimmy.com first

Let me know how this works out

A positive rating is appreciated thank you

Regards

Anthony

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Customer reply replied 2 years ago
Ok all the voltages are positive measuring from chassis ground.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

Its should have a negative supply and positive supply please swap the power thank you

Anthony

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TV Technician: Anthony_Infotech, Technician replied 2 years ago

If you are looking for component level repair with this that is not an option you must replace the board thank you as there are surface mount devices and other nasty things preventing this type of repair in most cases with TV its board replacement only even at workshop level

Anthony

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Customer reply replied 2 years ago
Ok I just found this video on youtube its the exact same TV power supply.
https://m.youtube.com/watch?v=Bf5T2wwtydYIs it possible its a bad LED strip? It looks like a lot of work to get access to it.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

Yes it could be but I can only make assessments by the info you supply and the way I see it that power-board is not working correctly, its possible the led array is bad and has damaged the power-board , there is no way to check the leds

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Customer reply replied 2 years ago
With all the lights off when I turn on the tv it looks like all the LEDs are lit. Is there any way to force the LEDs to stay on?
TV Technician: Anthony_Infotech, Technician replied 2 years ago

No they do not work a just being ON they are controlled

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Customer reply replied 2 years ago
ok thanks. I agree can't do board level repair, tried in past and pain in the but, easier to replace board.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

Yes unfortunately its nearly all board replacement now I take your point on the LEDs themselves but the way the sets are designed particularly this manufacturer and samsung they don't build in any help software to guide the technic***** *****ke a blink error report, and also nothing effective for checking so its basically down to experience and I would be swapping that board at this time

Let me know if you need more info

Anthony

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Customer reply replied 2 years ago
Ok I heard that the reason that the voltage jumps to 150V at startup is because one of the LED panel strips has an open circuit.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

Yes that could be but again its not conclusive there are many myth checks with flat panel Tv, the only sure way is elimination of the board, the good thing is in most cases you can send the board back and only pay a restocking charge

Anthony

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Customer reply replied 2 years ago
Hi Anthony. I decided to just take apart the panel to check the LED strips. There was a burnt led and a lot of other non working LEDs. Do you have experience taking these led TV apart. I have the diffuser and other sheets and not sure what goes in where.
TV Technician: Anthony_Infotech, Technician replied 2 years ago

No I don't get involved with that as its too invasive on the panel....sorry its the LED

Anthony

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Anthony_Infotech
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Category: TV
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