I wanted to post about my successful repair of a dead Samsung TV.
Model: UN55KS8000
Power Supply Circuit Board Number: BN44-00878A
Part required: SB5150 Schottky diode 150V 5A
Symptoms:
Powered TV on with remote control. Briefly (less than one second), saw video, then TV went dark.
- Not working at all
- No red LED
- No standby power
- Will not power on
Attempted reboot:
- Initially unplugged TV for about 20 seconds and plugged it back in (This has fixed this TV in the past when it was unresponsive.) Did not work this time.
Repair procedure:
- Removed five larger screws at the bottom of the TV
- Used a plastic wedge tool to pop the back off of the TV. There are no hooks at the bottom of the TV, but there are hooks about every five inches, located about three inches in from the edge of the TV all the way around the sides and top. The edge of the hook faces the sides and up toward the top. You might be able to lift the cover from the bottom middle and have the clips pop loose. I just pried around the perimeter of the TV. One hint - watch out for the IR detector and power switch at the bottom of the TV. It can be damaged if you are not careful.
- There are two circuit boards. One is the power supply board (located on the right as you view the TV from the back). The other is the TV processor board (located on the left as you view the TV from the back).
- You can confirm that the power supply is bad by plugging in the TV and measuring the standby voltage (no need to turn the TV on) at the place indicated in the picture. There is a jumper on the board clearly labeled with voltages when in standby and on mode.
- Disconnect the two ribbon cables from the power supply board by gently squeezing the sides while using a small screwdriver to back the plug out of the connector. Do not pull on the ribbon to remove the plug.
- Remove the two screws holding down the power plug on the power supply board. Slide the board gently to the right and it should be free.
I started by checking continuity of the fuse next to the power plug. It was fine. I then started to check all of the power diodes on the board based upon a repair video posted on YouTube. My thanks to 'Electronics Repair School' for the helpful post here --> https://www.youtube.com/watch?v=ZKsdGCkQKzo
(I used an ohmmeter with a diode continuity function, but I think any ohmmeter would work.) The video was not for my model of Samsung, but I figured they probably use the same parts, and so these diodes may have a problem.
As you can see from the picture, there are four larger Schottky diodes near the power transformer. Two measured as expected - open in one direction, .3 ohms in the other direction. However, the two closest to the heatsink both measured shorted in both directions. I snipped the leads on one side of both diodes so I could check them out of circuit. One checked normally, the other was shorted in both directions.
I ordered replacement diodes off of eBay, replaced the bad diode, and put the power supply back into the chassis. I plugged it in and measured the standby voltage at the test jumper. It was normal. I reassembled the TV, and it worked normally.
When reassembling the TV, be sure the infrared receiver/power switch is properly located before closing the case.
Model: UN55KS8000
Power Supply Circuit Board Number: BN44-00878A
Part required: SB5150 Schottky diode 150V 5A
Symptoms:
Powered TV on with remote control. Briefly (less than one second), saw video, then TV went dark.
- Not working at all
- No red LED
- No standby power
- Will not power on
Attempted reboot:
- Initially unplugged TV for about 20 seconds and plugged it back in (This has fixed this TV in the past when it was unresponsive.) Did not work this time.
Repair procedure:
- Removed five larger screws at the bottom of the TV
- Used a plastic wedge tool to pop the back off of the TV. There are no hooks at the bottom of the TV, but there are hooks about every five inches, located about three inches in from the edge of the TV all the way around the sides and top. The edge of the hook faces the sides and up toward the top. You might be able to lift the cover from the bottom middle and have the clips pop loose. I just pried around the perimeter of the TV. One hint - watch out for the IR detector and power switch at the bottom of the TV. It can be damaged if you are not careful.
- There are two circuit boards. One is the power supply board (located on the right as you view the TV from the back). The other is the TV processor board (located on the left as you view the TV from the back).
- You can confirm that the power supply is bad by plugging in the TV and measuring the standby voltage (no need to turn the TV on) at the place indicated in the picture. There is a jumper on the board clearly labeled with voltages when in standby and on mode.
- Disconnect the two ribbon cables from the power supply board by gently squeezing the sides while using a small screwdriver to back the plug out of the connector. Do not pull on the ribbon to remove the plug.
- Remove the two screws holding down the power plug on the power supply board. Slide the board gently to the right and it should be free.
I started by checking continuity of the fuse next to the power plug. It was fine. I then started to check all of the power diodes on the board based upon a repair video posted on YouTube. My thanks to 'Electronics Repair School' for the helpful post here --> https://www.youtube.com/watch?v=ZKsdGCkQKzo
(I used an ohmmeter with a diode continuity function, but I think any ohmmeter would work.) The video was not for my model of Samsung, but I figured they probably use the same parts, and so these diodes may have a problem.
As you can see from the picture, there are four larger Schottky diodes near the power transformer. Two measured as expected - open in one direction, .3 ohms in the other direction. However, the two closest to the heatsink both measured shorted in both directions. I snipped the leads on one side of both diodes so I could check them out of circuit. One checked normally, the other was shorted in both directions.
I ordered replacement diodes off of eBay, replaced the bad diode, and put the power supply back into the chassis. I plugged it in and measured the standby voltage at the test jumper. It was normal. I reassembled the TV, and it worked normally.
When reassembling the TV, be sure the infrared receiver/power switch is properly located before closing the case.
Attached Files
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