Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

[JA64Flyers]

Hello all! I've searched around on the forums for info regarding the above samsung and PSU/LED board, but haven't found any exact matches. The boards look pretty different from their predecessors so i figured i'd put this all out there.

The issue has to do with the back light. It will run perfectly for hours, even days, then the backlight kicks out until you change the source or power cycle the TV. Then it may come on for 5 minutes, or a few more hours. Its pretty random, i haven't found any patterns with it yet.

Since there's a picture, the internet tells me the TCON board is fine. Next is checking the power supply / LED controller (all one board here). I haven't been able to find a schematic or diagram for this thing, to tell me what my voltages should be or what points i should meter from. I understand that if i get normal voltages with the LED's unplugged, but wrong voltages with them plugged in - then it's an LED problem. If the opposite is true, its a power supply problem (cross my fingers).

Does anyone have any advice for getting that information? Thank you for your time!

[CapLeaker]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

Can we see the whole back side of the TV with all the boards connected?

First I'd see what happens to the BL-on (back lights) signal on the PSU (may be called BLUon/off) that comes from the main board. Is the BLon still present (something like 3V DC), when the back lights go off?
Next: Turn your back lights waay down to 40% or less and see if the back lights stay on longer. If they do stay on longer you have a LED problem and your boards are fine.

[JA64Flyers]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

Hey CapLeaker, thanks for the reply!

Attached is a picture of the full back and the connector you referenced with BLUONOFF. I'm having trouble metering the voltage from pin 20 without unplugging the connector, i'll get creative and fasten a paperclip to my meter lead or something. I can probably get in next to the pin.

Right now with the connector unplugged, it reads 4.5 vdc. I'll see what it goes to when the back light shuts off.

[JA64Flyers]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

More news! I can recreate the backlight going out by tilting the TV. When i tilt it forward about 20 degrees, it typically goes out. When it's laying down, backlight dead or alive, that pin reads 4.9 vdc. When i right the TV straight up and switch to another input (or powercycle, whatever "refreshes" the screen) it brings the backlight back.

Right now, i lowered the backlight brightness like you suggested, and it seems to have passed my "laying over" test and is running still. I'll let it go for another hour or so to confirm.

This leads me to believe there's a faulty connection in the LED strip somewhere. I've seen tutorials for other samsung models, any idea how i can tell how many strips i'll need to replace them? Is 4 strips common?

*Edit: putting any pressure on the back of the tv or lifting the corner can cause the problem to happen. Pretty much confirms the hypothesis in my mind.

[CapLeaker]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

I think you are on the right track.

[blowell]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

Hello everyone. I'm also debugging a backlight problem (video passes flashlight test, audio works, HDMI to PC enumerates as generic PnP monitor, etc.). I know main board is good and T-con board is good.

Does anyone here know which pins on CNL802A and CNL802B have the symmetric high LED driving voltage? And what should that driving voltage be (~170V?)?

Bob Lowell

[blowell]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

I think the high drive voltages are probably on the pins labeled "+" in silkscreen.

Does this sound correct?

[budm]

Re: Samsung UN60F8000BFXZA Backlight issue - Board BN44-00656A

Hello everyone. I'm also debugging a backlight problem (video passes flashlight test, audio works, HDMI to PC enumerates as generic PnP monitor, etc.). I know main board is good and T-con board is good.

Does anyone here know which pins on CNL802A and CNL802B have the symmetric high LED driving voltage? And what should that driving voltage be (~170V?)?

Bob Lowell

The expected Voltages are shown on the Voltage chart printed on the power supply/LED driver board.
https://www.badcaps.net/forum/attach...6&d=1483376884
The picture is too blur to read the prints.
the + is the Anode of the LED string, the - is the Cathode of the LED string.