Samsung UN75HU8550 vertical smearing

[funky3k]

I managed to score a free Samsung UN75HU8550! Unfortunately, the color is smearing vertically. The smears move with the picture and change related to other parts of the screen. It also smears on the settings menus, not just on input video.

So far I've gotten the main back panel off and did a visual inspection of the boards and reseated the cables connecting to the t-con and main board without any change.

If I flex the panel it does make the smearing slightly longer or shorter vertically depending on which way I flex it.

What should I try next? Based on the flex I'm thinking I need to get to where the cables connect from the t-con to the panel... or maybe the panel is just bad...

This would be a huge upgrade for me if I can get it working properly...

I'm happy to take more pictures and even video if it helps.

edit: I have access to a multimeter and potentially an oscilloscope and other test tools if needed.

[funky3k]

Re: Samsung UN75HU8550 vertical smearing

I removed the rest of the back of the TV to expose where the ribbon cables from the t-con connect to the panel. I tried lightly pressing on the connectors, both on the panel and the t-con, and didn't see any change in the smearing on the screen.

[funky3k]

Re: Samsung UN75HU8550 vertical smearing

Welp, forging ahead. (sorry for the solo forum blogging, this just seems like the place for folks with problems like this so I'm just having at it)

I got the shielding off near the top of the tv that housed whatever boards bridge the cables from the t-con to the lcd panel (photo 1).

Powering it back up... pressing on those boards, specifically the cables that join the boards on either side (photo 2 & 3) reduces the display corruption by like 50%! Hurray! Lets just clean those connectors and inspect the solder joints (photo 4) and power it back up with the boards free floating...

...and no change when pressing on the connectors independently from shifting the boards around. Pulling on the boards to put a little tension on the ribbon cables that go under the steel backing to the panel reduces the corruption around 75%... sigh. I guess we have to go deeper. The amount of disassembly required for the next step is a little concerning, but it is what it is I suppose.

[nomoresonys]

Re: Samsung UN75HU8550 vertical smearing

Looks like bad tab bonds, check youtube for shimming, works good sometimes if you can get the shims just right, can be a real pain getting them right tho.

[funky3k]

Re: Samsung UN75HU8550 vertical smearing

So I haven't been able to identify any bad tab bonds... one thing I did notice is that the distortion decreases when I just generally press down on the board (just the board, not the tabs specifically). Then I noticed that by pressing down the board it was increasing the contact between the conductive foam blocks under the board and the board's ground contacts. Directly connecting one of those contacts to ground pretty drastically improves the display... so now I'm wondering if it's a grounding issue or if that's just a red herring that's helping correct the real issue... the adventure continues.

[funky3k]

Re: Samsung UN75HU8550 vertical smearing

Well, the ground contacts on what I think are called the driver boards that have the tab connections all test out ok... They're around 0.2 to 0.3 ohms to the back panel.

So, I bolted everything back up and ran the TV for a little while and noticed that along the top of the TV the metal trim directly over the areas that distort get pretty dang hot. If I run my finger across the top of the TV it's cool where the picture is good and I can barely leave my finger where the picture is bad. Does anyone know what that indicates?

[funky3k]

Re: Samsung UN75HU8550 vertical smearing

I got back to troubleshooting this TV again after taking a break for a bit. I took off the outer metal frame to expose the flex ribbon cables that connect the driver boards on the back to the front lip of the panel. Once that was off it was very obvious the source of the heat along the top of the TV were the long Chip on Flex chips. The chips over the parts of the panel with the smearing got extremely hot while the others were just fairly warm.

By flexing the ribbon cable in different ways I was able to get the smudging to almost all go away, but not quite. Running a probe along the bonding between the panel and the ribbon didn't effect the display at all.

Does this point to an issue with the chips/flex cable or just a side effect of a problem in the panel?

[Davi.p]

Re: Samsung UN75HU8550 vertical smearing

Hi, it's reallly hard formeto understand all the posts without an internet translator, but i suspect the problem is in one or more chip on flat soldering, the problem is hard to outline to which one is the faulty tab and even if you find the one, are you able after to get the liquid glue remover and then do a reflow on it? The hot tabs are in the horizontal row or on the vertical part?

[Andrew F. Ali]

Re: Samsung UN75HU8550 vertical smearing

With the Chip On Film (COF) getting hot like that means the chip is on its way out and the only way to fix this is with a Tab Bonding Machine as the COF attaches on to the Panel. You could try tightly fitting heat removing foam between the metal frame and the chip surface as a temporary fix.

[Davi.p]

Re: Samsung UN75HU8550 vertical smearing

Andrew, i've read that COF chips are of BGA type soldering, if some balls make no good contact the resistance increase and it produces heat, not?

[Andrew F. Ali]

Re: Samsung UN75HU8550 vertical smearing

COF are attached to the Panel by Tab Bonding. Unless you have a Tab Bonding machine there is no way to repair this type of problem.

[Davi.p]

Re: Samsung UN75HU8550 vertical smearing

As i know COF=chip on flat, i was referring to the chip not the flat obvious.

[diif]

Re: Samsung UN75HU8550 vertical smearing

COF = Chip On Flex. As in flexible substrate.

[Davi.p]

Re: Samsung UN75HU8550 vertical smearing

??? The chip on flat is not flexible, have you ever seen a flexible chip? Flat cable, flex, for me it's about the same. Them are both not the right tech term.. that is FPC.

[anthonybalmert]

Re: Samsung UN75HU8550 vertical smearing

Sorry for the off topic question. I have been looking high and low for some intel on this TV and this is the first post I have found about it on the forums.

Funky 3k, can you tell how many LED strips are in this TV? Is it just the left and right sides or the top and bottom as well?

I have bright 3" wide bars on the left and right side of mine that disappear when the screen has a black background and grow brighter as what is being displayed does, and the rest of the TV looks dimmer than I remember before I recently noticed the issue.

Hitting it with a temp gun tells me there are only left and right edge LED strips working, the rest of the perimeter and middle of TV is a good 10 degrees cooler.

[Nick's Tvs]

Re: Samsung UN75HU8550 vertical smearing

Check the side tabs on the panel. If you find a bad IC that's burnt, you can rip off all the IC's on that side and it should clear up the issue. Don't do this without showing us pictures first, if you tear incorrectly then you won't be able to back track.