Hello all,
So my approx 4 year old TV is having issues. The model number is Samsung QN50Q60TAFXZC.
I had unplugged it for a week and then when I plugged it back in, the screen turned black but I was still able to hear the sound. So I decided to turn it off with the remote and when I tried turning it back on it got stuck in some kind of bootloop. The screen would turn on for a second then turn back off and the red LED would blink twice and it would repeat this cycle.
I tried all the basic troubleshooting of disconnecting it from power and connecting back or holding the power button for 30sec, holding the remote on/off button for 30sec but nothing seemed to have helped.
So my next step was to watch youtube videos and read ifixit forums to see how to open the back cover and get to diagnosing the issue. I tired by isolating one cable at a time to watch for backlight behavior. Here are my results:
(1) The first cable I disconnected was the one going from power board to main board. Plugged the TV to power and the backlight would stay ON so I concluded that the issue is downstream from the main board.
(2) I disconnected all cables that plug into the mainboard so that included the display ribbon cable, IR+WIFI+BT cable and speakers. Plugged the power back in and backlight stayed ON so I concluded the mainboard was fine too
(3) Now I plugged the downstream cables back in and watched for backlight behavior and I isolated the problem to the display ribbon cable.
(4) Next was to plug the big ribbon cable back to mainboard but remove the small flex cable that connects the two side of the panels at the bottom. Again plugged back into the power and backlight stayed ON. So I concluded that the issue is either this flex cable or the panel itself.
(5) Next step was to try the tape method and I started with selecting one end of flex cable and trying to block of 3-4 pins (the best I could with tools available to me). Plugged the flex cable back in and every other cable was also plugged in. Connected the TV to power and it would turn on and stay on but no picture, the screen is black. I pressed the SamsungTVplus button on my remote and it went to whichever random channel and I can hear the audio. I can also notice the backlight change intensity but the front of TV screen is till black and no picture/video is displayed.
At this point I am confused. I can't explain the behavior and I can't say what to try next. Was my diagnosis fair so far? And do you think the issue is the flex cable itself? or is it most likely the panel? If it is the panel, why doesn't it still display some picture even with couple of lines being taped off? Have I accidentally taped off the most important lines of the panel? How can I get a wiring diagram for the flex cable? If I can understand which lines are for clock/data/power maybe I can select the proper lines to tapeoff?
Please guide me on how to proceed further inorder to fix this TV. I want to try to fix it and not throw it away but I understand that if its a panel fault then it might not be worth fixing but I want to makes sure I have tried everything I can before I conclude that nothing further can be done and throw the TV out.
This is the image from main board side.
This is from the panel side.
These are the two halves of flex cable connector
Left:
Right:
The flex cable itself:
As for the voltages, this is the legend:
I was able to measure A13V as its easy to access and it shows up as 12.85V on my multimeter. I am assuming you would also like me to measure what the other pins are showing? But these pins don't have a rated voltage in the legend and I am guessing I will have to remove the mainboard and flip it around with some non-conductive layer in between so that I can measure the rest of pins with everything still connected. Looks a bit tricky to bend the ribbon cable while flipping the mainboard but if those are the signals you were interested in knowing the voltages then I can try to figure something out.
Cable with tap-off sections marked:
