Samsung UA50F5500 No Power to Some LEDs

[brodymc]

I've managed to pick up this TV from a relative for nothing.
However, it's got some issues: some of the LED strips don't light up.

I've done a little bit of testing and found that pins 10 (2+) and 12 (1+) on CNL802 have no power. Pins 6 (3+) and 4 (4+) have power.

According to the stats on the PSU board, it should be 274V (I think), but when reading the 2 pins that work (6 & 4), it reads between 350V and 360V (a lot higher than it should be). This testing was done with the LED strips disconnected. I also noticed that out of all the dead LED strips, the very bottom strip dimly flickers every couple seconds.

I'm pretty sure all the LEDs are good however, as I tested each individual one with my multimeter set to diode and they all lit up, so I'm fairly certain the issue is the PSU (just not what part specifically).

Full album of photos (with descriptions): https://imgur.com/a/Mc79u6S

Any help would be appreciated!

PSU Board: BN44-00612D / L55S1V DSM (equivalent BN44-00612B)

[CapLeaker]

Re: Samsung UA50F5500 No Power to Some LEDs

Yes, LED's can fail like that. They don't necessarily have to burn out like a light bulb. They can fail in a matter that they are not only to go out when they are failed short or open, but also if they get hot! If you have a backlight issue, first thing to always to do is to turn the backlight's waay down and see if the backlights stay on longer.
The 350V tell me that there is an open LED in one string or generally an open. That is because LED's are current controlled, not voltage controlled. Don't test LED's with your DMM in diode mode, you'd have to actually put power and current to them with a variable constant current / constant voltage PSU.
So all jammed together, it's not the PSU, it's the LED's!
Please use the attachment function to upload pictures.

[neilc6]

Re: Samsung UA50F5500 No Power to Some LEDs

I have found that connector going to the LEDs in that model can be a bit flakey.

https://www.badcaps.net/forum/showthread.php?t=72299

[brodymc]

Re: Samsung UA50F5500 No Power to Some LEDs

Yes, LED's can fail like that. They don't necessarily have to burn out like a light bulb. They can fail in a matter that they are not only to go out when they are failed short or open, but also if they get hot! If you have a backlight issue, first thing to always to do is to turn the backlight's waay down and see if the backlights stay on longer.
The 350V tell me that there is an open LED in one string or generally an open. That is because LED's are current controlled, not voltage controlled. Don't test LED's with your DMM in diode mode, you'd have to actually put power and current to them with a variable constant current / constant voltage PSU.
So all jammed together, it's not the PSU, it's the LED's!
Please use the attachment function to upload pictures.

I have found that connector going to the LEDs in that model can be a bit flakey.

I managed to get a hold of a power supply to test the strips. All of the strips tested OK.

Thanks Neil for the suggestion but I found that the connector had perfect continuity so that's not the issue either it seems. I can't seem to find a schematic or anything for this board either so it's fairing to be a bit of a head-scratcher.

[CapLeaker]

Re: Samsung UA50F5500 No Power to Some LEDs

oops, I've read your first post again. You stated that you did the testing with the LED's disconnected? That is wrong. Connect the LED's and measure the voltage on each string.

[nomoresonys]

Re: Samsung UA50F5500 No Power to Some LEDs

Looking like bad leds, replace all of them, BE VERY CAREFUL, screens are very delicate and break very easily, check some youtube videos if unsure about the process.