If you wish to execute auto repairs on your Derbi Mulhacen 125 then it is always a good plan to have access to a Workshop Manual to keep just for personal reference in the event you want to know how to remove a particular part for example, the Wheel Bearing and fit it again effectively.
Derbi Mulhacen 125 Workshop Manuals will give you specific diagnostic guidelines for your car therefore if something is not working it will help you determine what the issue is and how to correct it. You will be able to decide if you can do this by yourself or in the event the job is just too big you could book your Mulhacen 125 right into a trusted garage.
Derbi Mulhacen 125 manual