Advising people not to fix their phones themselves is one of Rukbat's favourite topics but I think he is right. I have seen a lot of threads here and elsewhere from people who have tried to fix their phone (usually replacing the screen) and ended up doing expensive damage.
If you are experienced working with modern smartphones
My take (as someone who spent years repairing them) is that anyone who has enough experience to repair one without breaking it wouldn't be asking questions here. I left the business a little before Android came out, so there are plenty of times I hit a glitch due to not being that experienced with Android. (By "not that experienced" I mean that I've never modified a copy of Android source and recompiled it myself, something I've done countless times with Linux.) But I don't post a question, I have enough experience to find the answer or, if no one else has ever experienced what I have, to bring the phone to someone who does. (Since I own Samsung phones t the moment, I head for Best Buy or my carrier, depending on the problem. My only working non-Samsung, a Motorola V551, isn't worth repairing, because I can probably find an equivalent on Craig's List for $10. And my Motorola Bricks and Startacs can't be used any more [but I'm sentimental], so I just keep them as reminders of a much earlier time.)
I figure that anyone asking how to replace a motherboard has never opened a phone before (it's pretty apparent to anyone who's worked on phones, but not the particular one he's working on now, where the motherboard is, which connectors have to be removed to swap it out and which screws have to be removed), so he's never unclipped a tiny ribbon connector, so he's asking for trouble. (I haven't worked on anything smaller than pressing the keys on my keyboard in a few years because I started developing cataracts, and if you can't read 4 point type without glasses or squinting, you have no business working on microelectronics. One cataract is now out, the other one comes out in 3 weeks, then there's about a month of healing before my vision will be good enough that a magnifier will give me the vision I need to see some of the components in a modern cellphone. Then we'll see whether my hands are still steady enough to work on one [which I doubt, but we'll see]. The last soldering job I did might pass in any electronics shop course, but not if I were the instructor. It worked, but out of 20 pins, I don't think the solder looked the same on any two of them. It should look identical on all of them.)
The same reasoning goes for people asking how to replace a screen or, worse, the glass on the screen. I've trained techs to do that sort of work for me. It takes the best tech a few broken screens before he can remove the broken glass and replace it without damaging anything. (Which is why good shops keep unrepairable phones in cartons in the back room. They're for techs to break when they're learning how not to break customers' phones.)
I have a few hot buttons when it comes to cellphones - this is one of them. It's usually cheaper to take the phone in for repair the first time, than after you've broken a few things. (One of my other buttons is how to get around the block on a stolen phone. This is androidforums, not Thieves' School. Buying a $600 phone in perfect working condition for $100 doesn't seem to raise any questions in the minds of a lot of people these days.)