I once fixed a broken guitar app for an elderly friend of mine. It was damaged during a lightning storm. He called the manufacturer, but they were from Europe and shipping it for repairs would cost more than a new amp. I offered to take a look, and after some probing with an oscilloscope and an AUX cable pushing some Mozart, I was able to find the signal stopped at a pre-amplifier at the input. I ordered a replacement IC for a few cents, and swapped it out. Worked like new after that. I was very satisfied to have saved it when the fix was so small.