3 years ago I started a a small repair business and I'm specialized in component level repair of measurement and calibration gear. See:
http://schneiderelectronicsrepair.nl/?page_id=29 And here : (
www.pa4tim.nl ) you see my gear and most of the home made gear I use. It started as a hobby.
I can not and will not make a quote because most times if I know the problem the repair is almost done. But customers who know me and trust me (the most important thing in this niche market) sometimes give me a max allowable cost. Will it make me rich, no, but that is for a part that I can only work a few hours a day because medical reasons. On the other hand, I really love doing it and I'm good at it.
If I did not already had most of the gear it would be almost impossible to start. Keeping your own gear optimal also cost time. And things like probes, soldering gear, testleads etc wear. Biggest problem now is space. Not only my gear but also that of customers, and things the boxes they send them in, and then there is parts.
Most stuff is 10-20 years old and without service manuals or schematics. It is expensive stuff and the value for the owner is the calibration history they have. But it depends on the instrument, I will do not do complex things like a spectrum analyser without service doc. My first customer and the one who stimulated me to do it commercially has an industrial cal lab, so a lot of repairs I do are industry related. Often temperature calibrators, drywells, oil/water baths, thermometers, portable process calibrators, so now and then a flowmeter. But also volt/current/resistance calibrators (a Valhalla, a few Flukes, a Datron) scopes, scopemeters, megohm meters, (a lot of G&M secutests) Also the more exotic things like a 3 axis fluxmeter, a vibration detector, (and unrelated a week later) an amp for a vibration table. Or strange things like a potted pressure sensor, it only took me 3 hours to get the pcb out. Had to desolder and resolder it through the cable entrance.
I also do repairs on things you can not power-up to measure like PCB's from some machine. I can test many components out of circuit because I have a lot of component testers (DIY made and commercial) and I know how to use it. I use things like a curvetracers, LCR meters and bridges, VNA, impedance bridges, a IC tester I build on the principle of a tubetester , signature analyse, fixtures for voltage regulators, opto's, several things to test transformers.
I repair PCB damage (done the repair of a inner layer a few months ago), I can wind transformers on my home made semiautomatic winder. But I also do mechanical things like making a new shaft for a switch or potentiometer, a switch, a connector etc You see some things on my site.
I do not, and will not do consumer electronics.
Fred