I need a diagram for the drive belt on a Quality Pro Lawn Tractor model #QPGT25H50A

When you say you need a diagram, do you mean so you can install a new belt? Most of the time if you just consider that the outside of the belt touches the idler/tension pulleys and the inside of the belt goes inside the V of a pulley and the belt fingers 'direct' the belt it is easier than it looks.

Attachment 48350

Attachment 48351

Not sure if this helps but it may