I got impatient flashing new firmware on the phone and corrupted the flash rom bad enough it was only booting up to the G1 logo and was getting ready to sell it for parts.
I checked Ebay and bid and won the same phone with a broken screen. Then I ordered the Ifixit tool kit and the day it arrived used your guide to swap the motherboard with the good one and poof, I now have a usable phone.
Go slow. Remember one sharp edge or screw and those ribbon cables can tear (I work on laptops) . The post op is it turned out the spacebar on the keyboard was bad but that's what the on screen keyboard is for.