Problem 4: Monitor goes to sleep at the end of the boot sequence when using iMac15,1 or MacPro 6,1 system definition
Fix: modify the AppleGraphicsDevicePolicy.kext
1.Using Finder locate this file /System/Library/Extensions/AppleGraphicsControl.kext
2.Right click and "Show Package Contents"
3.Now browse to /Contents/PlugIns/AppleGraphicsDevicePolicy.kext/Contents/
4.Open Info.plist using TextEdit
5.Scroll down to where you see <key>ConfigMap</key>
6.For the iMac15,1 locate the board-id "Mac-42FD25EABCABB274" and change string below it from "Config2" to "none". For the MacPro6,1 you will do the same thing but for the board-id "Mac-F60DEB81FF30ACF6".
7.Save the file.
8.Rebuild the kernel cache using the following two commands in terminal:
9.
sudo kextcache -system-prelinked-kernel
10.sudo kextcache -system-caches
11.
12.
13.Reboot
NOTE: you may need to use kext-dev-mode=1 if not already using it to allow the modified kext.