Thes sat/nav on my 740 stopped talking to me, and I found the fault to be with the disc reader.
I bought a replacment from eBay and fitted it.
It seems to be working fine the map shows where I am ect. but it keeps sending me in the wrong direction and it seems to think I am about 1/2 a mile away from where I acually am.
Does the unit need calibrating if so how do I do it?