I have 50 onn roku 4k uhd tv with bluish blacish screen.

Looks like it may be too old? Lots of help below, but this seems hopeful.

https://community.roku.com/t5/Roku-setup/Roku-Ultra-with-an-older-HD-plasma-TV-with-1080i-resolution/td-p/561009

Does a Roku Stick Work on Any TV? The Roku Streaming Stick 4K is designed to be compatible with any TV that has an HDMI port. This means it will work on both smart and non-smart TVs, as long as they have an HDMI connection.
If your TV is analog, don't worry! You can still use the Roku Streaming Stick 4K by using an AV Composite Converter. This will allow you to enjoy all the features of the Roku Streaming Stick on your TV.

All Roku streaming players will work for any television with an HDMI connection, so any Roku player can be connected to a 4K UHD or HDR-compatible television. However, to stream movies and TV shows in 4K UHD or HDR you will need a compatible Roku streaming player and television that supports 4K UHD or HDR.
Jul 24, 2023

Do I need a special TV? - Roku Support

Roku https://support.roku.com > en-ca > article

Does Roku Work on Any TV? Here's What You Need to Know

The Home Theater DIY https://thehometheaterdiy.com > does-roku-work-on-a...
2 days ago - Yes, Roku does work on basically any TV as long as it has an HDMI port. Older, lower resolution TV's probably don't need the most updated 4k ...

How to set up your Roku streaming player or ...

Roku https://support.roku.com > Roku setup
Jul 24, 2023 - From a USB port on your TV Any Roku Streaming Stick supports USB power, but only some Roku players do. If you are connecting your Roku device ...

‎Roku TV · ‎Roku Streaming Stick 4K · ‎4K TV · ‎Roku Streaming Stick 4K+

Compatibility Unleashed: Does Roku Work on Any TV?

Automate Your Life https://automatelife.net > does-roku-work-on-any-tv
1 day ago - The Roku Streaming Stick 4K is designed to be compatible with any TV that has an HDMI port. This means it will work on both smart and non-smart ...

‎Does a Roku Stick Work on... · ‎Steps to Install Roku on an Old...

LED backlights are bad, common failure on this model TV but if it were mine I'd recycle it and buy a better brand set.

Check for appropriate voltages going to the backlights from the PSU. If voltages are ok and still no backlights you may have to take the screen off and use a backlight tester to verify the individual strips integrity. This is tricky and you stand the risk of damaging the panel so be careful or get a professional to do it. If you are wondering why not purchase new backlights because everything else seems to be fine but the backlights are the only thing that's not functioning, that's because it is possible that the paper thin strip that connects all the individual backlight strips is shorting to the frame. We've had the same issue with this model and other brand/model that uses the same paper thin strip. We became aware that the strip was shorting to the frame by accident when we disassembled the screen an got to the backlights. We happened to be touching the connector strip and the metal frame and got a jolt and the backlights lit up momentarily when that happened. So we used a meter and verified there was a short. To rectify this situation (first verify that all your backlights are still good by using a backlight tester) then use a piece of electrical tape ( the length of the connector strip)and place the connector strip squarely an the tape providing extra insulation between the connector strip and the metal frame. If you don't have a backlight tester and you're just a do-it-yourselfer you can (since you are already at the connector strip) just proceed to use the electrical tape as described above and if you get backlights now then walla. You don't have to reassemble the screen to test if the backlights work. Just plug in TV and press the power button. The backlights will come on anyway. The pictures shows the connector strip placed on the black electrical tape.

Best advice here

https://www.fixya.com/support/r29790007-repairing_own_television

..

Question edited for clarity.
Question moved from Cooktops!

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I"m guessing it's the TV, chances are it would loose sound as well if it was the streaming service. Are your backlights staying on when the screen goes black?

Save yourself a lot of headaches and recycle the TV. This set was plagued with issues, even if you get it fixed it's just a matter of time before something else goes bad in the set. Next time by a name brand set and you will have better luck although none of them seem to last all that long anymore

Are your backlights lit?

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Mostly is the back lights strips, you may use a led check to check it out.