No back light on Samsung UN65MU6290, Need help modifying Power Supply
I just picked up this Samsung UN65MU6290 / PS board # BN44-00873C with no back light but otherwise fully functional (passed the flashlight test). My initial assumption was the LED strips were bad but upon further research apparently the Power Supply board can also be at fault for "over driving" the LED strips. On ShopJimmy they are recommending to replace some resistors and other components (transistors?) in conjunction with the LED strips (although their referenced Youtube link only demonstrates replacing the resistors):
"--PLEASE NOTE: This repair is recommended only for experienced technicians. After installing these LED bars, we strongly encourage you to perform the modification on the power supply board in your TV (BN44-00873C) that can be seen here: https://youtu.be/R_KuCkW1SO4
Replace resistors R9111 & R9211 as shown in the video with the included resistors from ShopJimmy.
After this modification is done, the LED bars will run much cooler than the stock ones and will prolong their lifespan significantly."
What has me especially paranoid is a comment I read from an eBay listing:
“On this model most of time one led strip and power board fail at the same time, to fix this issue you must replace that failed led strip plus power board. If you install this LED strip with failed power board and turn the TV on, LED strip will fail on the spot, also if you install a good power board with bad LED strips the same thing would happen to that power board. “
I need help approaching this cautiously and logically. I don’t want to unnecessarily buy LED strips if I don’t need them and I also don’t want to buy new ones and then fry them because of a fault in the PS board. I greatly appreciate any help diagnosing this. Tagging the experts who so generously help me time and time again.
I will post pictures of the board and LED circuit momentarily. I had no luck powering the LED strips from the harness but maybe I wasn’t doing it right. The harness seems to split into 2 sets of 4 wires. Each set contains a black wire with a grey stripe (ground?)
Photos of power supply board :
CNL802 is the connector/plug for the LED and I can’t make sense of the listed voltages in the diagram. I get about 317 volts on terminals 1, 2, 3 and 4. Terminals 5 and 6 which I believe are supposed to be ground I do not get a continuity reading. Terminal 7 I get minimal voltage: 0.12V and Terminal 8 : 0.02V. The readings are the same whether the harness is plugged in or not.
Hey guys. Sorry for the slow reply, I didn’t mean to ghost on this thread but I ultimately decided to go ahead and disassemble the TV to inspect the LED strips. They were trashed, totally burnt up. So I got a new set of LEDs from China and it took this long to receive them.
I installed the new LEDs which was kind of tricky, I somehow chipped off the edge of one of the LEDs but it still seemed to light up. Frustrating, but I continued with reassembly. I’m waiting on my repair kit from Shop Jimmy but have been deliberating about how many of the components I am even skilled enough to replace. I think the resistors should be simple enough but it looks like the kit includes a transistor and some other component/chip. I have no idea if I can / should attempt to replace these or what the impact of leaving them out may be.
Yesterday I became impatient and decided to power on the TV now that I have the new LEDs installed. I knew it was a risk but I’m already skeptical about the condition of the LEDs I reinstalled and if anything goes wrong with my PS board mods I would be left wondering if any issues were related to that or the LEDs. So upon plugging in the TV the backlight/LEDs came on right away and there was a buzzing noise, the backlight dimmed and I immediately unplugged the power cable. This was all within 1 second or less. I thought at this point I might’ve fried the LEDs again but was able to use my LED tester to power them on through the harness.
At this point I’m just waiting on the repair kit to come in the mail and I’ll go from there.
I received my repair kit and replaced the resistors at R9111 and R9211. I plugged everything back in and the LEDs are now flickering and the PS board is buzzing in sync. According to ShopJimmy this is a PS problem and their kit should fix it. There are no instructions to help me understand the intended location for these pieces or their function. Will report back with further progress.
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