Hello everyone,

I tried searching the forums for this same issue, but couldn't find anyone experiencing the same exact thing as me.

I have a TCL P605 purchased in 2017, and I can no longer adjust the backlight or the local contrast. The TV stays exactly the same brightness whether the backlight is set to 0 or 100. The local dimming also does not work, and acts as if local dimming is off, even when it is set to high. It is like as if the TV backlight is stuck to 100% brightness with local dimming turned off, no matter what settings I choose. This is the same for all inputs and apps I have tried. This problem also exists when watching HDR and Dolby Vision content, local dimming will not work.

This TV was turned off and unplugged for a month since the last time I used it. It was not moved during that time, just sat on a TV stand unplugged for a month.

Troubleshooting steps I have taken:

Checking and installing updates.
Factory resetting the TV.
Forcing the software update to be installed again through the first secret menu.
Factory resetting the TV a second time.
Turning off fast boot and the 4hr power saver.

Another wierd thing, is that when I go to system settings and do a system restart, the TV will restart, come up with the red TCL 4K boot screen, but once it loads the Roku OS the screen turns off but the TV continues to work. I am able to navigate around the menus using audio cues, and was even able to start Netflix and get a video to play with the screen turned off, but only audio was working. And the screen is actually powered off, the backlight isn't on, so it's not acting like as if its turned on but not getting a signal, which is a problem I have seen other users report.

However, if press the power button to turn off the TV and then turn it back on, the screen comes on then. It just wont come on after doing a system restart. And of course the backlight control and local dimming still do not work after a restart.

If anyone has any other recommendations I can try, I am open to all suggestions!

Thank you,
Chris


EDIT: Forgot to mention the software version. The TV is running 9.0.2 build 4035.

Hi Chris! 

Thanks for reaching out! A few questions to help better understand what you're seeing: 

- When did you first notice this issue?
- Could you provide an example of a particular channel and content title that you observe this issue on, and describe in greater detail? 
- In Setting>System>Power, if you turn on Fast TV start, does the display powering off issue persist? 
- What is an example of a HDR or Dolby Vision content title that you've observed the issue on, and which channel were you using to play that title? Did you try pressing the * key during plyback and adjusting the picture modes? 

I would recommend reaching out to TCL support to report the issue as well, and request additional support. Please feel free to send me a PM with more details, including your Roku account email address and the serial number of the TV from Settings>System>About. I'll follow up directly to see how else we can assist you from there. 

Thanks,
Tanner

I first noticed the issue this past Sunday, April 28, after updating the system software from OS 8 to OS 9.0.2. The TV had been unplugged and powered off since March 26, so it was off for a month before I turned it on this past Sunday. I used the TV for a couple hours that Sunday and the backlight and local dimming worked perfectly. Then i went and updated the TV, which updated it to OS 9.0.2, and that is when the backlight controls and local dimming stopped working.

As examples of channels and content, I use Netflix, Hulu, Crunchyroll, and Prime Video. I can pick any random video from any of those channels and can replicate the problem. I also have a PS4 Pro hooked up via HDMI 3 Arc, and also have the problem there.

Pressing the * key and changing the backlight from 100 to 0, or 0 to 100 makes zero changes in brightness or how the picture looks. The backlight acts as if it is set to 100, even when I press * and set it to 0. I can also press * and change the local dimming settings with zero change in the picture. Setting the local dimming to High does absolutely nothing, it does not turn on local dimming. Neither does setting it to medium or low. Local dimming stays off, no matter what setting I choose. And using a dark scene, such as any episode of Stranger Things, it is pretty obvious to tell if local dimming is working or not.

I posted this same issue over at AVSForums and there is at least one other person who has the same TV and the same problems with their backlight and local dimming not working after updating to Roku OS 9.0.2.

I'll send a PM later with my details and serial number when I get back from work. I will also contact TCL support.

@Chris311

Thanks! I'll keep an eye out for your details. 

Cheers,
Tanner

Hello,

I've been encountering the same issues reported here, and it's only happened after a recent update. Backlight cannot be adjusted within any service or HDMI input, and after restarting it goes to a black screen. Have never had any other issues, and I have the 55p605. Can you post back what the solution was?

@Kmoll 

Thanks for letting us know what you're seeing. We're still investigating the previous report. Feel free to send me a private message with more information, including your Roku account email address, the serial number of the TV from Settings>System>About along with the software version/build you have installed. I'll continue assisting you from there. 

Thanks! 
Tanner

Thanks for your patience here!

Please go ahead and try visiting Settings>System>System update>Check now and perform another system update. 

Please let me know if this helps clear up the issue you were seeing. 

Thanks! 
Tanner

It's fixed!!! Thanks so much.

I am having this same issue with my 55p605. I ran the latest software update to version 9.1.0 but I still can’t adjust the backlight. I’ve also factory reset it as well. Is there a fix for this?

@Clancemasterj

A few more questions here to better understand the issue you're seeing: 

- Where are you attempting to adjust the backlight settings from? The Settings menu on the home screen, or from the lefthand overlay menu accessible by pressing the * key during playback of content? 
- Are you trying to adjust this while on the Roku home screen, displaying an HDMI input device, or while streaming from a Roku streaming channel? 
- Have you tried restarting the TV from Settings>System>About? 
- As a last troubleshooting step, have you tried performing a factory reset on the TV? 


Thanks,
Tanner

I am trying to adjust the backlight from the * menu.

I’ve tried to adjust it from both HDMI and Roku channels.

I’ve rebooted and factory reset it. I’ve also ran all the updates.

Thanks!