To add to the list of repaired things:
1. Some years ago, we had a v. expensive Yamaha AV receiver that one day decided it wouldn't turn on, or rather, it would turn on then off immediately. I was quoted by a Yamaha agent £150 for repair, plus postage plus parts plus any additional repair time. We came to the conclusion this wasn't worth pursuing so bought a new non-Yamaha receiver.
The old one was a big thing and I hadn't the heart to throw something so large and complex away, so it sat in the back of my shed for several years. Eventually, I realised this was a waste of time so in an initial clearout, out went its remote control. The next week, I hoiked out the receiver to take down to the tip. However, something nagged so I googled various terms for the receiver's fault. Up came a power supply issue affecting different receivers but they were ones in the same series as mine. The fault was a single open circuit polyester capacitor, costing a few pence, in the power supply board.
Five minutes later, I was peering at my PSU board. It looked a bit different but there was exactly the same component in it. It took me ten minutes to remove the board and another five to remove and solder in a new capacitor that I already had in a box of spares. Plugged the receiver in, pressed the power button and it burst into life. I then regretted throwing away the remote the previous week! The unit is too old to use in the house now but it makes a great radio and amp for the workshop.
What is really annoying is that the fault info was only eventually leaked. It was well known at the time the receiver went wrong and looked upon as a lucrative source of engineers' income as it was so quick and cheap to repair.
2. My old 2005 Honda CRV aircon stopped working, leaving one light on the controller flashing. The answer, according to my Honda dealer was £500 + labour for a new controller unit. Google was my friend. The controller had a firmware bug which shut it down after a given number of uses, typically about 3 years worth. It could be reset by a wierd combination of key turning while holding down various buttons and pressing another to put the aircon into diagnostic mode. After that, the aircon worked again and was still working two years later when I sold the car.