TCL U55C7006 TV does not start

[janos6662000]

Hello
I received from a friend from Norway a faulty TCL U55C7006 TV
TV had a white power led on when powered on, later the LED went off, but no picture.
Initially i thought that it has a bad backlight. I tested the led strips with a tester but they proved good. I also checked the screen with a powerful flashlight, but no sign of any signal on screen.
I made some research and i discovered that the TV is an Android TV and the fault i have is often connected to a firmware problem.
I downloaded some firmware images and made some trials.
I tried with 3 different USB sticks, size ranging from 2-8GB, formatted FAT32 (in the end i also tried FAT16) and different firmware images. I used USB sticks with leds to check activity.
When i power on the TV, LED shortly lights on, then off.
Sunday i forgot the TV on and i left. When i got home, i saw that the TV has backlight. I flipped it over and i saw some pinkish garbage on screen. I switched off the TV and back on.
This time it had the TCL logo, later animated, then the Android logo and eventually it booted normally. I got a screen saying (in norvegian language), that no device is connected to HDMI3.
This proved that none of my firmware writing attempts was successful. but also the fact that the display itself is OK.
Tried to enter some menu with the joystick, nothing happened.
I thought that probably the joystick is faulty. I programmed a universal remote for this TV, when i got back, the TV did nothing with the remote.
I switched it off and back on, but since then only the pinkish garbage, sometimes the TCL logo, but TV does not boot.
I obtained the service manual but until now i didn't find any abnormal voltages.
As i see it now, one secondary voltage does not work correctly and stabilizes in time. The motherboard is powered only by 12V from the power supply. That voltage does not vary.
Of course, when i don't have backlight, the BL_ON voltage is missing. Other than that, i didn't see any differences yet.

Please advise.

[nomoresonys]

Can you post some clear straight on pictures of each board and one of the whole back as to see how everything is connected. And one of the pinkish garbage.

[janos6662000]

Can you post some clear straight on pictures of each board and one of the whole back as to see how everything is connected. And one of the pinkish garbage.

Here are some pictures.
Pink stuff is not always the same, i even saw a few times the TCL log, on normal picture.
Since then i never left it to warm for hours, so i never got sunday's result again.

[tiki66]

Here is SW for your TV:

https://mega.nz/file/wtYWHYCT#6iktYW...Jq_Pjg6hjSpxnw

(V8-T658T01-LF1R820_Test_Version.zip)

Download SW and unzip it. Put Upgrade.pkg directly on root of usb stick. Stick must be FAT32 formatted.

Unplug tv, insert stick, press power button ON TV and keep it holding while plugging in tv in socket. Upgrade procedure should start.

[nomoresonys]

Check the side panel for the reset recess, use a paperclip or the like to press it, hold for about 30 seconds or til you see the front indicator light up a little, release it then try to turn tv on as normal.

[janos6662000]

Here is SW for your TV:

https://mega.nz/file/wtYWHYCT#6iktYW...Jq_Pjg6hjSpxnw

(V8-T658T01-LF1R820_Test_Version.zip)

Download SW and unzip it. Put Upgrade.pkg directly on root of usb stick. Stick must be FAT32 formatted.

Unplug tv, insert stick, press power button ON TV and keep it holding while plugging in tv in socket. Upgrade procedure should start.

Hello tiki66
Thank you for the firmware.
I tried, but unfortunately no success. I still think that this is a hardware problem. Even the P_ON signal appears after a looooong time (10 of minutes.)

[janos6662000]

Check the side panel for the reset recess, use a paperclip or the like to press it, hold for about 30 seconds or til you see the front indicator light up a little, release it then try to turn tv on as normal.

Hello nomoresonys
Thanks, but this mainboard doesn't have a reset button, i checked carefully.

[nomoresonys]

Could be an hdmi problem, maybe try heating the hdmi chip for a couple minutes with a hair dryer then try tv, see if it does anything different. For this test just use a hairdryer NOT a heatgun.

[howardc64]

I've not seen this model but since its low end brand (TCL) and Google TV, maybe likely it suffered the eMMC failure so common for Google TVs?

Here is a HiSense Google TV I debugged with this problem ( link )
Nick's TV has a ton of videos on SONY's Google TV with eMMC failure ( link )

Low end brand like HiSense also puts HDCP, Netflix and streaming app keys in the dead eMMC so even if new eMMC is firmware installed. Still lost all keys so streaming and HDMI won't work. SONY was smart enough to put the security keys in separate memory.

If replacement main board is expensive and mostly out of stock, it usually suggest the typical high Google TV eMMC failure and only repair unfortunately is board replacement if can't rebuild eMMC and/or keys are in the dead eMMC.

I don't know why Google TV have such high eMMC failure rate. Low end TVs likely use lower capacity eMMC (faster wear) and Google TV may have some abusive level of flash memory writes. For example, excessive logging which is fairly common computer developer approach. I have a 2013 Tesla Model S and they also ruined the entertainment console's eMMC within 4-5 years by over logging.

[nomoresonys]

Any update on this?

[janos6662000]

Any update on this?

Sorry, i was a little busy, will get back adter i check.