My stereo amplifier quit amplifying over the weekend. The LEDs still lit up, and it would still pass audio through the "tape out," but nothing went to the speakers. So, I decided to take it apart and see what I could find...
Step 1: Open it up
Pull the cover off, and expect to find something obviously wrong.
When there's nothing obviously wrong, make disapproving noises and have your house-mate phone his brother to see if the brother still has an extra amplifier. When it turns out he doesn't, carry on to step 2.