Fixed dead Samsung UN50NU6900F

[howardc64]

Looks like a common problem. Remote powers on power light with only high pitch squeal (and eventually cycling 3x) from the all-in-one board (main+PSU+tcon). No picture no sound. With the rear cover removed, squeal sounds like it came from main board section under the heat sink (which doesn't make sense of course but maybe just due to all-in-one board design) Here is a sound sample, turn up volume to hear.

https://youtube.com/shorts/oc5PQiZkQ8g?feature=share

2 PSU section caps were bulging. Replaced both of these fixed the TV. Spec is 470uF 25V and only reads 120uF after removal.

Here is how to open the back. See the pic showing the plastic fingers on the rear plate clipping onto the metal frame+wire. Do both sides and top first and bottom last. Bottom separates pretty easily with a flat screw driver parallel to bottom face. On the bottom, don't jam it inside where all electronics, wires, and speakers are.

https://www.youtube.com/watch?v=NtQs...l=Paul%27sTVCo

Commenter Lord Xibalba in the following video had the exact same problem which makes me think a common problem.

https://www.youtube.com/watch?v=JXVq...l=TVPartsToday

This TV repair service indicate they've seen quite a few failures on these low age sets (Mine was 2019)

https://www.youtube.com/watch?v=mCle...ellTVRepairLLC

[neilc6]

Re: Fixed dead Samsung UN50NU6900F

NU series has lots of backlight failures due to edge lit design with lower number of LEDs running brighter and hotter. Rare to see cap failures in LED TVs. Have never seen one personally yet.

[howardc64]

Re: Fixed dead Samsung UN50NU6900F

NU series has lots of backlight failures due to edge lit design with lower number of LEDs running brighter and hotter.

Thanks for the note. I run all LED TVs at 50-60% backlight for longevity. But TV manufacturers love to default to max to for showroom comparison haha.

[howardc64]

Re: Fixed dead Samsung UN50NU6900F

Question for people with this TV

- The chassis randomly clicks. Electrical taped all the fingers and all 4 edges on the rear plate that clips onto steel wires and noise still occurs. Some of the clicks occurs when changing videos (say youtube) The backlight will fade dark and then brighten during the video transition. Maybe related to thermal expansion of the hotter edge lit LED bars? Edge lit LED bars usually have 2sided thermal tape underneath. I've dis/reassembled Apple's monitor with LED bars. Will get clicking if the thermal tape is disturbed and uneven. I wonder if these edge lit Samsung LED bars often have thermal cycling noises.

- Also get vertical bar section on LED briefly (like 1+ frames) but pretty rarily. Mostly same region on the LCD but once in a different region. Look just like failed LCD edge flex cable issue. Perhaps the integrated main+PSU+tcon board has some noise as 2 caps previously failed. When TV is powered off... very faint sequeal from the board for a littlewhile.

Anyway, chassis clicks is quite annoying. Seems quite common on this set from online search. Anyone experienced this and have solutions?

[howardc64]

Re: Fixed dead Samsung UN50NU6900F

Update for future DIYer

Random clicking sounds

Samsung has decided to go screwless on these. Basically snaptite construction everywhere. I taped everywhere the rear case snaps onto the chassis and the 2 metal leg mounts where its metal on metal contact. Clicking seems quite a bit less.

Another clicking sound occurs often on changing video sources (switching tv channels, streaming video etc) I think the reason is Samsung decided to dim the LED during the video source transition to make it look nicer (can see backlight doing this transition effect with the back panel off). This probably thermal cycles the edge lit LED which seems to sticky tape mounted without any screws. Probably loosens over time. Perhaps the fix is to replace edge lit LED bars with new sticky tapes and likely not worth it until LEDs burns out. Samsung can also remove this dimming video transition feature from the firmware but probably unlikely at this point.

Vertical noise bars

Looked like classic LCD edge flex connection issue but only very brief and infrequent. Turns out to be TV's youtube app streaming 4k video (over 2.4GHz wifi) TV broadcast and firesticks work without any problem.

[alfatv]

Re: Fixed dead Samsung UN50NU6900F

I am fixing the same model right now.
Noticed some buzzing noise coming from main board.
Narrowed it down to one of these 2 inductors, they are in backlight circuit.
Tone of the sound correlates with amount of backlight.

[howardc64]

Fixed a 2nd one. Exact same 2x bulging 470uF 25V caps as post #1 Put in higher quality 35V 470uF. Hope it outlast other parts of the TV. Also blew off the dust bunnies that gather around parts for the other failure below.



Since Power LED lit up and hearing squeals, wasn't this other common problem with a blown fuse + other parts. Lucky me, simpler problem and fix

https://www.youtube.com/watch?v=mCleFWXEVYk
https://www.coppelltvrepair.com/p/21...ed-pfc-circuit

Also no clicking sounds snapping the rear cover back on. I think likely because I took it off correctly (pop left. right, top, and tilt up cover to get bottom off rather than prying it off which probably breaks something)

[EazyBone]

While I didn't fix mine (pads got messed up some reason) I had the same exact issue with it also. So glad to see this confirm that would of probably fixed it.

[howardc64]

I've repaired quite a few electronic items with failing 470uF ~25V caps. First was a fairly common garage door opener failure. It was a filter cap in the AC to DC 4 diode bridge rectifier circuit. Maybe similarly designed on this board?

[CapLeaker]

While I didn't fix mine (pads got messed up some reason) I had the same exact issue with it also. So glad to see this confirm that would of probably fixed it.

I am still running an older MU series bought in 2017 every day. No problems… so far so good for an 8 year old TV.