My phone died when I plugged it onto a car charger. It would not charge the battery using cable or wireless charging. It would not power up even after charging battery in external charger. Microsoft said it was 6 months out of warranty and it would be about $200 to have it fixed.
The Lumia motherboard and smartphone toolkit form iFixit were perfect. I was able to open up the phone, remove covers and pin connectors with the tools, then put in the replacement motherboard. It booted up immediately and did its long upgrade process to upgrade to Windows phone 8.1 denim update. All phone components work with new motherboard and I have a good as new phone again. I uploaded a few photos that show various stages of phone disassembly and finally show the fully restored phone turned on to the Glance screen.
I found it very useful to run/pause a YouTube video on my PC showing the complete disassembly of a Lumia 830. It showed how to carefully remove some key parts using tools provided in the iFixit toolkit. The video is here — https://www.youtube.com/watch?v=xJumqaAq...
I also suggest setting up all backup features of your phone now before the unexpected power failure like mine occurs. There is no way to recover pictures or files if the motherboard cannot be powered on.