Once you start talking about repair at a chip level (on the actual logic boards inside your phone or laptop) things get a '''lot''' more complicated when it comes to troubleshooting. Depending on the problem you ''might'' get away with just a multimeter and some general tips, or you might need an oscilloscope, an electrical engineering degree, and original circuit diagrams to figure out exactly which chip is misbehaving and why.
Sometimes it's as simple as a blown resistor which can be fixed with solder sucker, soldering iron, and 5 cent part. Other times a microcontroller had its flash memory wiped in a power surge, which requires a multi-thousand dollar logic analyzer, an AVR programmer, and access to the original compiled bytecode to reprogram the chip.
In the case of phones and other small electronics, many of the chips on the board are simply too small to be resoldered by hand, even for a trained professional. Repairing those chips requires an expensive hot-air rework station, or if you're talking about cracked cold solder joints on a BGA package, you might be totally out of luck. It might literally require starting all over with a clean board, laying down fresh parts with your pick and place machine, and running the whole thing through your reflow oven, assuming you can get the manufacturer to cough up the reflow profile.
I think you see what I'm getting at. :)
Replacing the logic board as a single piece is, right now, the sweet spot for anyone to be able to repair their electronics, and that's what we're targeting at iFixit. We want to teach everyone how to repair everything, but it's a bit crazy to expect people to all get electrical engineering degrees to be able to do that.
Besides, if we were all electrical engineers, jokes like, "Hey baby, you must be 0.7V and I must be a diode because you're turning me on!" would get old really fast.
