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Hi and welcome to the site, I’m Louie. Sorry you had to wait awhile but I’ll do my best to help.
Initially, bear with us; re-confirm and post back with the complete model number of the Dynex.
Appreciate the additional information.
Consider an experiment (if have not been done). Power on the TV and set to a program/channel. If at all possible, darken the room where the TV is. Wait for about 5 minutes or more. Shine a flashlight at an angle (not directly) and nearly but not touching the screen where the volume level / menu display is usually seen. Press the VOL UP/DOWN or MENU button and note if a dark/ghostly image of the volume level or MENU could be seen.
The above is a test to determine if it is a backlighting issue.
The described symptom then would point to an internal hardware issue.
Are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter ?
If no multi-meter, then we can not perform any voltage tests.
The repairs would be a blind board replacement to serve as both an attempt of a repair and as a test by process of elimination.
A replacement board would have to be purchased online.
Would you be comfortable proceeding with this approach?
That reply on blind board replacement was in response to "... What if I don't have one (multi-meter)?..."
I can "...walk me through trying to repair the problem..." but with the use of a multi-meter and even perhaps a soldering iron.
Perhaps you would prefer an alternate approach / second opinion to your concern.
The question would be re-opened as I would rather opt out.
Still, good luck with the Dynex.
If we have pushed through with meter tests / board replacements, I could also have posted potential online sellers of pulled out / refurbished replacement board(s) that sells for less than $50 CAD
Sorry but no; no multi-meter (readings) = diagnosis is guess work.
I already have opted out twice! However, everytime you reply back, the question is thrown back at me.
I have provided the means/answer as above posted even the "...no multi-meter...blind board replacement to serve as both an attempt of a repair and as a test by process of elimination..."
Please be patient and wait until somebody else picks up the problem and post their reply.