If you want to conduct maintenance to your Yamaha DT50R then it will always be a great idea to possess a Workshop Manual to keep just for reference should you need to know the best way to take off a specific part for example Brake Discs and install it again properly.
Yamaha DT50R Workshop Manuals are able to offer identifiable diagnostic info for the car so if something is wrong it will help you discover what the problem is and the way to repair it. Then you are able to assess if this can be done on your own or in the event the job is simply too big you can book your DT50R in to a suitable car garage.
Yamaha DT50R manual