Hi,
Its just they did not have the detail usually associated with schematics.
A circuit diagram is a tool you use not just to design, but troubleshoot.
The more complete the schematic, the easier it is to fault find.
You may need to look at this recommended L200 circuit with bypass capacitors on input and output, I hope the caps are located as close to the L200 pins as possible.
Glad you found your problem.
Tom... 
