ipod wont dock

ipod classic 160gb will not dock with compatible dock

dock works great with ipod nano and iphone 3gs

it states it is compatible

This is a replacement ipod that apple sent me after having a new battery fitted

so it has strange firmware on it

iTunes says it is up to date etc etc

I have tried restoring it etc etc

I have rebooted it etc etc

Out of warranty so cannot take to apple store