Samsung un58tu7000fxza - Power cycles with no picture, only backlight

[brad2157]

I have a Samsung un58tu7000fxza that powers on (no image, only backlight) but keeps restarting. When it starts up, the backlights seem to be full brightness for 1 sec., off for 1 sec., on again with much lower brightness for 4 sec., full brightness 1 sec., off 6 sec., then repeats. I noticed when the backlights are off, I don’t see the red optical audio port lit, meaning the main board is power cycling. The T-Con must be integrated in this model, because there’s not a separate board. There’s a power board, main board, and driver boards (if that’s what these are called) that are connected directly to the screen ribbon cables down across the bottom. On my main board, there is only one ribbon cable that feeds these driver boards. If I disconnect it, the the TV stays on with backlights at full brightness. I read these models often suffer from bad screens. I did the tape trick to block off some pins in the ribbon and also was able to get the TV to stay powered up without restarting and even heard the start up audio, as well as audio when I used the remote to select menu, etc..). I never could get an image up, but only different line patterns of different colors depending on what pins I had masked off with the tape. I’m trying to isolate the issue to to determine if I have a faulty main board or bad panel. Sounds more like a panel issue since the main board stays powered on with the ribbon disconnected going to the driver boards, but the tape trick never made anything appear on the screen (startup logo, menu text, etc..). Any ideas or suggestions on where to go from here?

Here are the voltage measurements.

TV on with ribbon cable from main board disconnected:

1-GND (0)
3-A13V (12.93 VDC)
5-A13V (12.93)
7-A13V (12.93)
9-A13V (12.93)
11-GND (0)

2-ANA-DIM (3.36 VDC)
4- N.C (0)
6- BLU_PWM (2.88)
8- POWER ON/OFF (3.30)
10- GND (0)
12- GND (0)


Main board disconnected - nothing connected except LEDs (connector snaps directly into power board when installed)

1-GND (0)
3-A13V (12.93 VDC)
5-A13V (12.93)
7-A13V (12.93)
9-A13V (12.93)
11-GND (0)

2-ANA-DIM (3.13 VDC)
4- N.C (0)
6- BLU_PWM (3.30)
8- POWER ON/OFF (4.54)
10- GND (0)
12- GND (0)

[brad2157]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Any ideas at all to help confirm?

[dskall]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Can you get some good pictures of board along the bottom?

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

I just got the same model, only FXZC at the end.
The symptoms are mostly the same except SAMSUNG word shows up briefly.
It's out of warranty, the original owner took it to Samsung and they quoted 900CAD to repair it which certainly means bad panel.
Also the owner said it happened suddenly while watching TV.
Hoping to find shorted cap or similar.
I will post pictures of panel boards after I do some checks.

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Left side (looking from the back)

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Right side (looking from the back).
TV boots up with this side disconnected, there is backlight, but no image

[brad2157]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Can you get some good pictures of board along the bottom?

Sorry for the delay. I usually get notifications on comments / replies, but I didn't receive any for this post (unless it happened to go to my spam folder).

Here are some pictures of the TV. Let me know if you need more up close pictures. Thanks for your help!

[brad2157]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

I just got the same model, only FXZC at the end.
The symptoms are mostly the same except SAMSUNG word shows up briefly.
It's out of warranty, the original owner took it to Samsung and they quoted 900CAD to repair it which certainly means bad panel.
Also the owner said it happened suddenly while watching TV.
Hoping to find shorted cap or similar.
I will post pictures of panel boards after I do some checks.

I was thinking it's most likely a bad panel as well, but wanted some confirmation before I scrap it. I checked all the caps on the “driver boards” on mine and didn't see any issues there. The tape trick, blocking some of the pins on the ribbon cable did keep the TV on, but I never could get any image to display (menu, etc..), although I did hear the audio tone when selecting menu, etc.. from the remote. The best I got on the screen were a few lines of different colors. That was slowly testing by covering a few pins of the ribbon cable at a time until the TV stayed on and didn't power cycle.

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

If you disconnect the cable between panel boards, does TV stay on?

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

So, we posted pictures, any LCD experts out there?

[dskall]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

So did you check for shorts on bottom boards? Voltages?

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

No obvious shorts, the voltages are cycling on and off

[dskall]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

And you have good picture on one side?

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

No picture with cable between sides disconnected, but TV stays on.
Anyways I got image to show up with scotch tape, however the brightness on bad side goes up and down every second or so.

Also found this discussion, looks like similar issue:
https://www.reddit.com/r/TVRepair/co...000f_bootloop/

[dskall]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

Does t-on power cycle or other voltages. Do they cycle with one side disconnected?

[alfatv]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

What is t-on? The voltages are stable with one side disconnected.

[dskall]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

You need to do some ohms checks on voltage points.

[JeffN9]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

I have the same tv with the same problem. Has anyone found a solution? If tape method worked which pins did you cover? If replacing or completely removing components on the buffer board, which? Tried a replacement main board which did nothing.

[nomoresonys]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

sometimes you have to play around with the width of the tape(how many "pins" are covered) look on youtube, here's one of probably 100 videos you can look at: https://www.youtube.com/watch?v=jlmzLXjCJ_4

[JeffN9]

Re: Samsung un58tu7000fxza - Power cycles with no picture, only backlight

I didn't quite find 100 but 6 or 7 videos show the tape method of covering several pins to get a decent albeit not perfect picture. All of the videos I found show tv's with two ribbon cables, my tv has only one. Looks like a real crap shoot trying to figure out which to block.