Samsung UE32F5370SS / UE32F5570 / UE32F5070 LED - No Backlight

[Foppel]

Dear all,

i try to repair a UE32F5370SS with a non working LED Backlight. I checked the voltage for the LED's at the cap. I got 180V. The LED Voltage was 160V. I bought another TV with smashed screen for spare parts. Try to change the Power Supply and the Mainboard and all the cables => Same Error. Now i disassembled the Panel and try to swap the LED Backlight from the Smashed Screen to the other one. The Backlight unit was easy to disassemble. I will check the non working Backlight unit and will post the result here.

Mainboard: BN41-01958B
Power Supply: BN44-00607A
LED Strips: BN41-02032A (LED Interface FHD32" Sharp)

I need the service manual for this TV. But i cant find anything.

best regards - Foppel

[Foppel]

Re: Samsung UE32F5370SS / UE32F5570 / UE32F5070 LED - No Backlight

Damn after i changed the LED Background i smashed my LCD

I found one faulty led in the non working backlight unit (open circuit). And yes they are all in series The led driver is about 160V / 320mA. I counted 45 LEDs. 160V / 45 LEDs give me a voltage of 3,55V for every LED. The current is always the same 320 mA. That means you need a Lab Power Supply with 32V to test the stripes. I use my 20V Lab Power Supply to test the stripes. 21 V was okay to test 8 Leds in Series. If you dont have a big power supply to test you need a lot of time to test every Led once by once

When i was a child i unplug one bulp from our christmas tree lights and everything was dark. It was hard to find which was the faulty bulb after that It's the same with this background LEDs.

cheers - Foppel

[int0x13]

Re: Samsung UE32F5370SS / UE32F5570 / UE32F5070 LED - No Backlight

Hi, did you manage to solve the case finally?

[Foppel]

Re: Samsung UE32F5370SS / UE32F5570 / UE32F5070 LED - No Backlight

Hi, did you manage to solve the case finally?

Yes the Problem was solved. I tested the LED stripes and i found one dead LED. The device worked well after changing the LED Stripe

[budm]

Re: Samsung UE32F5370SS / UE32F5570 / UE32F5070 LED - No Backlight

" The led driver is about 160V / 320mA. I counted 45 LEDs. 160V / 45 LEDs give me a voltage of 3,55V for every LED. " Actually, the Vdrops on the LED string is 45 LEDs x 3 V = 135V, the other 25V is the Vdops on the PWM Controlled power MOSFET and the Isense resistor for maintaining the constant current through the LED string.
BTW, always use power supply with current limiter when testing the LED strips since if the LED strip had shorted LED then the current through the string can be higher than the LEDs can handle.
Also always turn down the backlights level the reduce the chance of LEDs failure.

[dskall]

Re: Samsung UE32F5370SS / UE32F5570 / UE32F5070 LED - No Backlight

And if you are going to be working on tv regularly an led tester is a great tool