TCL 49S405 double image

[howardc64]

LCD displays a 2nd image slighty offset vertically. And multiple pairs of black lines along the bottom. Probably common as google "TCL 49S405 double image" pulls up this ifixit post ( link ) with identical ( nearly, but their fault seems to be on the other half of the panel than mine ) problem without solution.

This one looks to be a more difficult to diagnose because most? of TCON seems integrated ( CSOT BGA on buffer baord) into the left panel edge board ( looking from rear of TV) There are 2 buffer boards for each 1/2 of the screen. Main connects to the left buffer board where TCON is, then flex connects left buffer board to the right board. Disconnecting the right board gets double image on the left half and white on the right half. Unfortunately, with TCON integration on the left buffer board, can't disconnect the left half of the panel while driving the right half.

No shorts on all the caps on the left buffer board.

There are 1x to 4x pairs of black lines cross the bottom of the panel (see pic) When TV is first turned on, there will be 4x pairs. After few seconds, 3x pairs, after about 1/2 min 2 pairs and couple of minutes later, only 1x pair remain which unfortunately never goes away.

No circuit at the outer ends of the buffer board looks like gate driver line resistors I can remove like an LGs I previously fixed.

Randomly masking off main to left buffer board connection doesn't fix anything as expected on this integrated design.

Any suggestions how to go about this ultra integrated more difficult panel to diagnose the faulty component?

[EazyBone]

Panel short. Not fixable. That's my thoughts.. try and Google fixing TV with tape.

With these TCL when you disconnect each half of TCON you will see full half image on each side. If screen is fine will be no lines or defects on either side.

[howardc64]

Panel short. Not fixable. That's my thoughts.. try and Google fixing TV with tape.

With these TCL when you disconnect each half of TCON you will see full half image on each side. If screen is fine will be no lines or defects on either side.

Thanks, unfortunately can't do the typical trick of disconnecting each 1/2 of the panel and tape trick. Connection path is main -> left buffer board -> right buffer board noted in the original post (probably too wordy). Disconnect left and you lose the connection to the right. And tape is not going to matter since tape is blocking main -> left which then also kills the right. So no way to mask one edge signal and use the other edge.

But I found the smoking gun and will follow detail pics in next post.

[EazyBone]

My pics weren't loading. Would of got the data lol. You are correct though. But still seems like a panel. But curious what you found. Will see update

[howardc64]

Think I found the smoke gun on the failure.

Outer most buffer board to panel flex cable on both left and right shows LC2 signl trace is discolored. Was able to trace continuity of LC2 probe point next to the timing chip to outer edges of both buffer board's discoloration traces on the outer most flex. Right buffer board also has label LC2 on this trace.

Here is the CSOT timing chip (on left buffer board) with LC2 probe point (red arrow)



Here is outer edge of right buffer board with LC2 probe point (red arrow) and flex trace discoloration



Here is outer edge of left buffer board with probe point just above A of GOA (red arrow) and flex trace discoloration. Probe point is continuous to LC2



So unfortunately, damage seems to be in the panel/COF on both left and right side. Likely can't cut one side and depend on the other.

However, since my panel exhibit the problem with right buffer board disconnected. I suppose cutting the left buffer board's LC2 and relying on the right side may potentially offer a solution. But since right side LC2 trace is also discolored, perhaps wishful thinking.

I suppose if I have fancy flex bonding machine to bond to board and glass and a replacement flex with COF on there, its a potential repair but who has those equipment haha.

====

As for why this failed, here is a possible theory. Maybe design weakpoint similar to an LG design failure I fixed (post #7)

https://www.badcaps.net/forum/troubl...74#post1776374

The metal guard for the buffer boards runs flush against the COF flex. COF will be just a tiny flex gap away from the metal guard which is a big ground rail. The outer most COF+flex carries the highest voltage for driving panel gates. On the LG, guard rail naturally scraps the flex during assembly.



I wonder if thermal cycling over the years of use eventually cause weakpoints in the COF flex insulation?