Old, 50 years ago everything came with a diagram. Today,o diagrams, most will buy new.
I've fixed many chargers, none had diagrams. If you have seen one charger, you have seen most. Difference is smart chargers have a brain box. I've repaired golf cart chargers my by-passing a defective brain box and installing a timer.
Sit down with pencil and paper and make your own diagram. It's not that hard.
Is there something special about the Schumaker Battery charger?
I've found the things that seem to go bad are usually in this order:
Power cords have an open.
Switches go bad.
Brain boxes get damaged by a power surge.
Wire connection internally burn off.
Defective circuit breakers.
Occasually diodes burn out.
Have fun, LOL