UN65TU7000 strobing / flicker

[howardc64]

Good picture but has ~200Hz+ faint flicker/strobing over entire screen. Also has a single green vertical line. Can mask out t-con signals (2pins) to stop flicker/strobing but 1/12 of screen will be all colorful vertical lines (single green vertical line is in this section)

Since can mask t-con signal to disable part of the screen and stop flicker/strobing. Obviously not backlight.

Panel has 4x driver boards each responsible for 1/4 of the screen. 3 tabs on each board. Each tab responsible for 1/12 of the screen. the 2 outer most tabs has additional horizontal gate control signals.

No shorted caps on edge boards. No COF damage marks. All voltage readings are reasonable. Each of the 12 tabs does have a cap that reads OL but tab traces reveals the cap is disconnected (maybe just put there for common design for panel variations) I did desolder/resolder with one of them thinking I found the problem until high resolution pics reveals all tab flex has 1 cap on a dead end trace.

I guess slight chance could be main+tcon board but seems quite unlikely as the single green vertical line likely indicate panel internal damage and flickering will stop if the t-con signal for the section containing this green line is masked.

Can probably live with the single green line but strobing / flickering is bothersome on darker content regions. In particular flat monotone color areas without image patterns to distract the eye. So far, only way to stop strobing / flicker is to disable 1/12th of the screen.

[howardc64]

Re: UN65TU7000 strobing / flicker

Update. Probably bad panel. Here is info in case anyone have ideas

Problem

Screen flickers. Most visible with solid dimmer colors. But not visible when nearly black or white. When running gradually dimming grey test (youtube video). Flicker appear to the eye @ ~50%

Has 1 permanent horizontal line and 1 permanent vertical line. Green lines on following pic is drawn to indicate the location



Masking 2pins from t-con to panel

Screen flicker stops IF masked 2 pins from t-con (on main board) UN**TU8000 service manual ( link, my TV is UN65TU7000F ) has identical t-con connector and 2 pins are (connector PDF attached below)

TX_CH10_A+_USIT
TX_CH10_A-_USIT

There are 12 channel pairs and 2 t-con to panel flex. 6 channels on each flex.

Masking 2 pins create static vertical lines for 1/12 of the screen.
If masking only 1 of 2 pins. Will get running horizontal or vertical lines (depending on which pin masked) in this region.

The masked 1/12 vertical line region contains the permanent vertical line.



Other Masking Solutions

Tried many other random masking efforts. Only time flicker stops is when 1/12 region containing permanent vertical line stop displaying properly 100%. For example when entire 1/2 of the screen containing permanent vertical line stops displaying)

Voltages

All voltages appears normal on buffer board. Cap #7 goes to 0v when 2 pins are masked.



main t-con output TX channel pair voltages are (t-con/panel connected and unmasked)

TX_CH10_A+_USIT, = 0.582v
TX_CH10_A-_USIT = 0.574v

Other pairs are 0.575 for A+ and 0.568 for A-

Misc

Pressing on buffer board flex contact doesn't help. Can't reach flex to LCD glass contact

Maybe small chance its main/t-con? All multi-meter checks on buffer board looks normal.

[howardc64]

Re: UN65TU7000 strobing / flicker

I think I've narrowed down the problem. Posting here for experts to chime in.

Problem

• Screen has a permanent vertical and horizontal line. In post #2 but attach again for easy reference.
  
• Screen has faint flicker/strobing effect. ~5Hz. Hard to camera capture (video compression noise) but human eye detects it easily. Here is best I can do, strobing is fixed frequency (video doesn't show after compression noise) Video is just a section of the screen (video of whole screen can not capture the strobing) https://youtu.be/ORIlKf3j0ZM

Masking T-Con to Panel Flex

• TV has main with integrated T-Con and 2 flex to panel buffer boards. Panel has 4 buffer boards so each T-Con flex goes to 2 buffer boards.
  
• Any masking that turns 1/12 vertical section containing the single green vertical line to all static vertical lines will stop the strobing. CH7+-_USIT pair (pin65/66) is provides pixel data for this 1/12 of the screen. If mask SFC1(pin 80) which is probably a clock for all pixels on the flex will cause static vertical lines on 1/2 of the screen, strobe also stops. Here is pic masking CH7+-_USIT pair
  
• If mask just 1 of the CH7 lines, 1/12 vertical section will display horizontal or vertical dynamic streak patterns and strobing effect will be worse.
• Masking 1 pin on other channels will also produce dynamic streaking lines (on other 1/12 section of the screen) but no strobing effect.
  
• Post #2 shows CH10 which is incorrect. It is CH7

Diagnostic Analysis

• USIT is probably Samsung's version of V_by_One HS ( link link ). This is basically high speed long distance SerDes+CDR (Clock Recovery) data transmission for larger 4K+ panels. Pixel clock is embedded in the signal to display the pixels in the channel.
  
• Masking out CH7 stopping the entire screen strobing means the CH7's source driver (in the COF) is affecting all the TFTs on the panel. Most likely VCOM shown as "common electrode" here ( link ) This video summarized the source driver functions inside the COF (shift register->latch->level shift->DAC->buffer)

Multi-Meter Probing

Using multi-meter AC mode, I believe I am seeing 1v+ AC noise on VCOM.



Luckily, I have an exact same working TV to compare with

Working Panel

• Probe points at the buffer board near the edge of the panel (near CKV* CKVB*)
• A = 6.26v DC 0v AC
• B/C/D = 8.2V DC 0v AC
• A is ~5-6ohm to VCOM1_CELL (pin 6) 50ohm to FB_VCOM1_2_CELL (pin5)
• B/C/D doesn't connect to T-Con flex directly but probably connected to common electrode somehow.

Failed Panel

• A= 6.4v DC 0v AC
• B/C/D = 7.7v DC ~1v AC!

Failed Panel with CH7+- channel masked out

• A= 6.4v DC 0v AC
• B/C/D = 7.3v DC 0v AC

Next Steps

Anyway, seems like no way to repair this panel. I may try to remove/replace some caps on CH7 buffer board section but doubtful that will achieve any results.



X = AVDD_17V_PW (15.24v DC 0v AC)
Y = HAVDD_8.5V_PW (7.65v DC 0v AC)

Since I also have a horizontal line, maybe a chance masking gate driver clock lines (CKV*, CKVB*) may help. Will also try that next.

[hispeck]

Re: UN65TU7000 strobing / flicker

Hello friends, I have a similar tv . Mine will not turn on. The light will blink when trying to come on. I tried to insulate some track it came on with bars

[howardc64]

Re: UN65TU7000 strobing / flicker

Hello friends, I have a similar tv . Mine will not turn on. The light will blink when trying to come on. I tried to insulate some track it came on with bars

Should post in a new thread unless its exact same model. Yours looks like a Samsung curved screen TV? Also sure to follow these 2 stickies with a post similar to my post #1 in this thread

https://www.badcaps.net/forum/showthread.php?t=24661
https://www.badcaps.net/forum/showthread.php?t=39740

Also show pic of what tracks you masked off.

[howardc64]

Re: UN65TU7000 strobing / flicker

Traced the ~1V AC circuit which is the source of the strobing brightness flicker to a VCST signal on the buffer board.



B=C=D=J= VCST
E=AVDD_17V_PW (on CN1300)

For reference. Following were used to find VCST. Buffer board labels aren't clear which point they refer to
F=VSS2 (buffer board label) = VOFF_-11V_PW (on CN1300)
G=STVP (buffer board label) = STVP1_GOA (on CN1300)
H= VSS1 (buffer board label) = VSS_OUT1_CELL (on CN1300)
I = GND

C and D are empty pads with GND open pad directly above them... Perfect for 1-2 filter cap (1uF? 10v MLCC ceramic surface mount) to remove the AC noise...

VCST

I think VCST = Voltage Correction STored according to this Samsung patent for improving side viewing of VA panels (this TV is VA panel). I don't really understand how it works but it calculates a correction voltage based on histogram analysis of the image.

https://cdn.badcaps-static.com/pdfs/...d306a33339.pdf

But clearly any regular AC ripple noise on here will cause a ripple to the liquid crystal rotation and therefore brightness strobing.

My panel damage probably shorted a source driver lines to a VCST TFT.

Soldered Filter Cap for VCST

2x 1uF 0402 MLCC ceramic cap (one on each half of the panel) Unfortunately no difference. VCST AC is ~.7V compared to previously ~1V. But Still brightness flicker...