Hello
The belts are fine tensioned before to ship the mount and usually don't require adjustment for the user.
In case due to specific user requests we can send the tutorial to perform this easy operation.
However, before to adjust the belts tensions, can you please send us the phd2 log file and the setup specs?
You can send this informations also via mail private message.
After we will analyze it we can have more informations for provide you the best suggestion.
Best regards.
Stefano
Avalon Instruments Team