Chosen Solution
As of now, my after turning on my TV, I can see the backlight turning on for a second or two, then turning off for a second or two, and endlessly repeating this cycle. Background: This began to occur a couple days ago when I was playing a game on my Xbox One, which was connected to the TV through my receiver. Mid-cutscene, the picture became darker (but still visible) and then vertical green lines appeared over the image, growing and moving horizontally across the screen. Once I realized this wasn’t some weird-ass cutscene thing, I turned everything off, waited a minute, and turned the receiver back on, which also powered on the TV via CEC, and then the power cycling began, which I eventually narrowed down the the TV behaving as I described above. I took the back off the TV to see if I could find any obviously bad capacitors, but from what I can tell (I am no expert) they all look pretty good to me. I was hoping somebody here could give me any advice and/or guidance. Thanks!
Update (07/16/2020) I did some more testing/experimenting/bumbling and determined that the TV will not power cycle when one half of the cable going between the power board and the main board is disconnected (it’s the “northmost” connection on the “east” side of the main board, see picture).
After realizing this, I reconnected it and then powered on the TV after disconnecting one of the cables coming out of the main board, one by one sequentially. I also tried disconnecting both ribbon (FFC?) cables coming out of the mainboard simultaneously. With each test, the TV still continued to power cycle. So, I think the problem might be the cable going between the power board and main board. I tried finding it on samsungparts.com, but the only cables listed there are FFC cables, so I’m not sure how to go about getting a replacement. Thanks in advance for any ideas!
Hi @weezyfiggs Try the following: Disconnect the power from the TV. Disconnect the cable between the power board and the mainboard. Reconnect the power to the TV. The TV screen backlights should turn on full and stay on. There will be no picture because the mainboard is disconnected. If the backlights don’t stay on or they blink then there is a problem with the power board or the LED array. Disconnect the power from the TV and then disconnect the LED power cable from the power board. Reconnect the power to the TV and then check the voltage at the power board’s LED power cable connector. It should measure ~ 250 - 280V DC or maybe even as high as 300V DC If it is not that high or is pulsing it is a power board problem. If it is steady it is a LED array problem. If the backlights stay on, check the voltages at the power board’s mainboard cable connector and see if they are as per what is marked on the power board near the connector. If they are as marked and also steady then it is a mainboard problem
Normally, most TVs will power up after a few seconds of turning on power to allow the PSU to stabilize. When the relays activate, if there is a problem with other powered circuitry, as in an abnormal load, it will then shut down and start the power cycle again. Disconnecting a cable would point to the board that has a problem. However, if that board is connected to another circuit the problem might be in that circuit. This follows Brandon’s find of burned resistors off the main board. Replacing the resistors will not solve the problem until the cause of the burn is found. A schematic will tell you what the resistors power, and of course, if the resistors are burned only a schematic will tell you what the value is. Otherwise, it is replacing parts till you get results, which can become more costly the a new TV.
I have been working on a 75" Samsung UN75RU8000FXZA that is in eternal boot loop. Removing power from mainboard allows all LEDs to light normally (LEDs good). Removing ribbon cables from mainboard (TCON and mainboard now in a single board) allows TV to boot- I can hear the boot sound and TV stays on. Tried a replacement mainboard with the same results. Upon digging, it looks like part of the display is faulty, causing the boot sequence to stop and try to restart upon an error. I will try to isolate whether its the left side or right side of display. From video I found online - you can then slide plastic under parts of the ribbon cable to try and isolate the bad section of display but still allow it to boot. From the video I watched- the tech suspected the chip-on-film going from buffer board to display has gone bad on one section of the display.
