Nissan Micra K12 Trip Computer

Hello everyone!

I had a mechanic put in a AUX/iPod cable back to my original stereo. Thing is, afterwards the trip computer stopped working. It got backlight, but it doesn't show anything on the display and it doesn't react when I press any buttons. The mechanic says "it's a common problem, sometimes they just stops working" which sounds like a bs excuse to me.

What's the most probable problem when the trip computer is lighting up, but still doesn't work/display text? Can I fix it somehow? I could really need some help here. :)