stock head unit volume

i have a 07 tundra sr 5 stock 6 disc player , what im having an issue is this , when i turn the volume up ,it goes down and vise versa, sometimes it the volume numbers only change a a couple numbers no matter if im turning it up the volume goes down and so do the numbers ,just wondering if anyone else had the issue and was it a simple fix or did you just put in another headunit

 

Sounds like you need a new HU. Considering it is 18 years old, you got your moneys worth out of it.

Id just replace it, it will sound better and have more features.