I have recently gotten a hold of several Samsung TVs with bad backlights. Unlike LG TVs which shut down the backlight if failures are detected, Samsungs will continue to run leading to failure of almost every LED. Damage to the power supply could also occur. For most Samsung TVs, disconnecting the cable from the main board to the power supply board should light up the backlights. Here is a list of models and the corresponding LED strip part numbers I have encountered .
UN40EH5300FXZC, UN40H5203AFXZC – both use a 3 strip setup with 2 angled strips and 1 straight strip. Part numbers LM41-00001V/ LM41-00001W or D3GE-400SMA-R2/ D3GE-400SMB-R2
UN46H5203AFXZA, UN46EH5300FXZC – LM41-00001X / LM41-00001Y or D3GE-460SMB-R1 / D3GE-460SMA-R2 or BN96-28769A / BN96-28768A I have encountered damage to power supply BN44-00771A (traced to a bad diode D9801C) on one TV.
This TV attempted to turn on (the front LED would flash) but there was no backlight. With the main board cable disconnected from the power supply board, the backlights came on confirming the power supply and backlights were good. This test indicated the problem was with the main board. Searching the part number BN94-05113J on ebay found a few expensive used boards and one repair service indicating the board suffers from BGA connection failures on the main processor. Shopjimmy had a long list of substitute boards and I was able to find a more reasonably priced one searching the BN97-06022A part number. This board part number was BN94-05038B and was from the 40″ version of this TV UN40D6000SF.
With the new board installed, the TV turned on and also didn’t need anything changed in the service menu.
This model didn’t have built in wifi (requires dongle or wired ethernet) and youtube is no longer supported.
This TV turned on but the backlights were very dim. Disconnecting the cable from the main board to the power supply board had the backlight light up but at the same dimness. Probing the connector to the LED strips with an LED tester got very low voltage and unusual readings. Searching the power supply part number BN44-00771A on Shopjimmy got a warning that this model was prone to LED backlight failure.
With the TV apart, I could test the strips directly and over 50% of the LEDs had failed. Some were visibly black. I have found new replacement strips on Aliexpress (search 2013SVS46) which have been ordered.
With Samsung TVs, the power supply appears to not shut down the backlight when there is a LED failure unlike with LG TVs. This appears to lead to a higher number of LED failures since people will continue using their TVs. Hopefully, there is no damage to the power supply board with so many shorted LEDs.
I previously had to do a full backlight replacement on model UN50EH5300F with one or two LEDs out on every strip.
Update: The strips came in and TV has been repaired. I checked the screen settings and the TV had been running in Dynamic mode which runs the backlights at maximum brightness. There is an option in the settings to apply the picture settings to all sources when I reduced the backlight level to 12.
The LED strips I purchased from Aliexpress were from seller KCLCD Store and the brand is Rzconne. It was shipped using tracked epacket.
When the power button is pushed, the front LED blinks but the TV doesn’t turn on. Unplugging the main board from the power supply, the backlight flickers. Checking the strips with an LED tester, they all test good.
The voltage across the leads on the big main capacitor go the expected 390VDC. Checking other voltages, B5V was at 5.2V but B13V was unstable drifting around 11V +/- 1VDC. Since B13V supplies the LED driver IC, this unstable voltage was causing the flickering.
The power supply board was BN44-00645D and I found a schematic for BN44-00645A. The suffix is usually a different revision but compatible part number.
Checking the components around the unstable part of the circuit, the capacitors all tested good.
Since I couldn’t find the fault, I ended buying a replacement board on Aliexpress. With the new board installed, the TV powered up.
I have a stand for a 50LN5750 that was missing screws from the base to the upper support. The manual describes them as P4 x 25mm. They are actually pan head Phillips self tapping screws (4mm diameter). LG part number appears to be FAB31740201 and a part site wanted a whopping $5 each with $10 shipping. Found some good suspects on Ebay shipped from China (search M4x25mm self tapping) but ended up finding some locally from a LG dealer. In a pinch, the closest imperial screw is a #10 – 1″ which is 4.8mm diameter and the thread pitch is a little wider. The screws to mount the stand to the TV are standard metric machine screws and the part numbers can usually be found in the user manual.
Got this monitor in which didn’t turn on. It uses an external AC power supply as most LED monitors. The TV has only one main board inside and I was able to find a used on on ebay. Part number BN94-07215A.
When the replacement arrived, the monitor behaved exactly the same and didn’t turn on. I then noticed the connector to the LED backlight had broken off and was not making contact to the edge lit strip. I disassembled the panel down to the strip but improperly mounted the connector back and overworked the solder pads. During testing, something shorted on the main board as well and I had burning component smell from it.
There is a small blue led in the bottom right corner and it can be configured to be on with the monitor on or in standby. If you don’t know the current setting, it can be confusing to determine if the monitor is on or off if the backlight doesn’t come on.
Since I had the second main board, I was able to find a replacement edge lit strip on Aliexpress.
Once installed, the monitor worked with everything put back together and I am able to upgrade from my reliable 22″ Samsung LED monitor. It would be nice to have a 1440p or 4K monitor since the 27″ just gives bigger pixels at 1920×1080 resolution.
This TV turned on but had no backlight. The owner indicated the TV was set to dynamic mode which cranks the backlight level to maximum.
With the TV opened up, visible damage was found on several LEDs on the left strip. The right strip tested good with an LED tester. Searching the part number 2012SVS55 7032NNB LEFT76 2D (hidden beneath a covering label) found a similar part with a 3D suffix and a 10 pin connector. The 2D version uses a 6 pin connector and I wasn’t able to find this version online. I did have 3D strips salvaged from another TV. With the 6 pin connector, only 3 pins are used and the entire strip can be lit by applying power across pins 1 or 2 and pin 5. The strip has 76 LEDs wired as 4 separate banks of 19 LEDs. Two banks are wired in series and these in turn are wired in parallel giving approximately 114V (38 x 3V) drop across the entire strip.
Wires going to the left strip were black (-), black (-) and white (+). To create a single strip, I shorted pin 3 to pin 4, shorted pin 7 to pin 8 and wired black wire to pin 1, black wire to pin 6 and white wire to pin 10. If I kept the original cable to the 10 pin LED strip, it would have made wiring easier.
Another option would have been to replace the LEDs themselves but my reflow station was melting them and a hot plate may be needed to replace them. They are surface mount and appear to be part TS731A (lots of sellers on Aliexpress).
With the TV assembled, I did notice some mistakes I made during reassembly. I left some finger prints on the clear plastic panel which were visible on the screen if the image was clear and light. I also had tore edges of the reflector white backing paper behind the plastic panel. I had taped the torn pieces back up but it created some bright spots on the edge of the screen.
For disassembly instruction on Samsung edge-lit TV’s, see this post.
This TV had no power and the service manual can be found here
I checked fuse F602 and it was open. The main switching transistor Q601 was shorted gate to drain. I checked the diodes in the secondary output and one of the SB3A0H diodes was shorted as well. With these three parts replaced, there was still no output on the AMP+13V and P-ON+21V line.
With Q601 shorted, there would have been unexpected high voltage at the gate and components connected to it may be damaged. I found a repair kit on ebay which gave clues to which components to check. Probing the circuit, I found D607A (27V 500mW Zener) questionable, Q602 (2SC5334S NPN 30V 0.8A) questionable, D608 (36V Zener) shorted and R611 (0.3ohm 2W) open. D609A (schottky diode) tested good.
Here is a parts list with Digikey substitutes.
F602 Fuse 2.5A 250V 507-1180-ND
Q602 IRF640 N-CH MOSFET 200V 18A IRF640NPBF-ND
D608 Zener 36V 1N4753A-TPCT-ND
R611 Res 0.3 ohm 3W PPC3W.30CT-ND
Q602 NPN 125V 0.8A BCX41TADICT-ND or 45V 0.8A BCW66GLT1GOSCT-ND
D653, D655 SB3100 SB3100FSCT-ND
D607A Zener 27V SM TFZVTR27BCT-ND (can substitute leaded axial part and place in D607)
With all these parts replaced, the TV powered up. The heatsinking for Q602 is inadequate and probably caused the initial failure.
This TV wouldn’t turn on but the front LED would blink once when the power button was pressed. Typically if you have a front LED (indicating you have standby voltage) and the TV doesn’t power up, it is a main board issue. I probed the PS_ON and DRV_ON signals on the main connector and didn’t detect a DRV_ON signal so I ordered a replacement main board. When I installed the replacement board, it behaved exactly the same way. I ordered a used power supply board next and it was pretty inexpensive at under $20 USD shipped. When I plugged it in, I noticed LEDs light up on the main board which weren’t on before and the TV powered up.
I should have done a more comprehensive job of checking power supply voltages before concluding the main board was bad. Luckily the seller takes returns so I will ship it back and take the hit on shipping charges.
This TV did not turn on and would click every few seconds.
This youtube video indicates to check for shorts on transistors for the LED drivers on the power supply board.
Power supply board is BN44-00358B. Schematic is available online here
There are 4 transistors Q9101, Q9104, Q9201 & Q9204 and I found one shorted and previously replaced. I ordered replacements on Digikey part#FQU5N40TU-ND (Mosfet N-CH 400V 3.4A Ipak) and replaced all four proactively.
This board may also have an issue with blown fuses which means you should check QP801, QP802 and CP808 for shorts.
After replacing the transistors, the TV powered up but one side was dim. This was traced to loose connections on the LED connector.
Update: The TV came back with a dim side again which I suspected was a power supply fault. I ended up buying a compatible substitute board from the Chinese company buyqual.com which ended up fixing the problem.