Need Help with Gilera DNA 180

Hi all,
I do have Gilera DNA 180 and my problem started couple weeks ago. Tachometer keeps jumping up and up. So when it is idling instead of showing 1650 or 1700 RPM it might be showing 3000 or sometimes 5000 RPM. Engine still works on correct RPM range but Tachometer display is wrong ofcourse when you riding 90 Kmh showing RPM is wrong as well. And some times after you stop it takes couple times turning the key on and of so needle drops back to zero.
I got the tachometer get it repaired but they couldnt find any foult. Can some body pls help me Im going crazy. Nobody can`t seem to find the mistake. I live in Australia by the way. Thanks heeps on advance guys and girls.

Hi guys I ended up answering my own question. lol. Problem was the Tachometer itself. I did change the hole instrument panel its gone now but now my speed display is MPH instead of KPH anybody knows how to change that?