After reading other comments it seems what you're really needing is a diagnostic guide instead of a repair manual. There aren't many things that have diagnostic guides, as those doing repairs are expected to know how to diagnose.
The simple breakdown of diagnosis is: what is it not doing that it should? How would that logically happen? Go to that point and test. For example, the drum never spins when it should. The drum is spun by a belt, is the belt broken? Fix it. Not broken belt? What moves the belt? A motor, test the motor. Is it getting power as it should? Yes, bad motor. No, what feeds the power to the motor....... and on and on until you find the problem.