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Samsung TV Continuously Turns on and off (power cycle)

Hi,

I have a 50” Samsung TV model number UN50TU8000FXZA, I dont know much history about the TV. There is a date of 2019 on the power supply board. I have done the following troubleshooting so far:

Symptoms:

When plugging in the TV, the Samsung logo comes on the screen, and within 1-2 seconds the logo becomes partially garbled, and additional 1-2 seconds the tv turns off and then turns back on, starting the cycle again. When plugging in the tv, i can see the leds on the back go through 3 stages of brightness and on the last (when they are the brightest) the logo comes on. I reseated all internal cables with no change in symptoms.

Steps done so far:

  1. I checked all capacitors on the power supply board, no bulging tops.
  2. I left the TV plugged in for about 5 minutes and the cpu on the main board registered 125 degrees F. Seems hot for a resetting/non functioning cpu, but i dont know what to expect.
  3. Disconnected the cable to the main board. Plugged in the TV, the LEDs come on and I measure the following voltages in order at the LED connector on the power supply: 209V, 171V, 171V, 96V.
  4. On the power supply board, the voltages for the main board connection are as follows: 1-G, 2-G, 3-13V, 4-3.3V, 5-13V, 6-3.3V, 7-13V, 8-0-1.4V, 9-13V, 10-0V, 11-G, 12-0-1.6V. Pins 8 and 12 fluctuate between 0 and 1.4/1.6 volts, it spends about 3 seconds at 0 volts, then changes to 1.4/6 and drops back to 0.

Does anybody know if these voltages are in spec? the pins at 13V are correct, there is a label on the board, but the remining pins are descriptions, not voltages. I’m wondering if pin 6 should be 5v? Anybody have any other steps I can try? I can’t really find much in the way of schematics online, so i’m kind of stuck as to where to go next. I really hate to throw money at parts, i’d rather have make an educated guess. My initial thought from what i can tell is the power supply seems ok, it is puzzling i dont see 5V anywhere, which is what drives a lot of electronic boards. I suspect the main board but hoping there is a way to further diagnose.

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Commenti:

Update: I unplugged the ribbon cable from the mainboard to the LCD panel, plugged it in and it seems like it booted! Nothing is on the screen, but the LEDs changed brightness a few times, then stayed on constant and i got some kind of boot up sound out of the speakers.

da

2nd update. The main ribbon cable plugs into a long and skinny circuit board that has a ribbon cable connecting it to another long and skinny board. These two boards have additional ribbon cables that come off and (i think go to the lcd panel?). When i disconnect the ribbon cable between the two circuit boards the tv boots. ugh.. i dont think there is much else to do? bad panel?

da

3rd and last update. I was able to replace the buffer boards, a real pia, i do not recommend. It did not fix the issue, i must have a bad/shorted lcd panel. TV went into the trash.

da

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Here’s what Samsung says to do:

https://www.support.com/how-to/how-to-fi...

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I did this 5 times, with no change, thanks tho.

da

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A power fluctuation may be the reason for the error. Also don’t forget to take your TV adapter(if present) for a physical examination and see if the capacitor on the power unit is working.

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Guy in Desert sarà eternamente grato.
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