Chosen Solution
All, When not connected to an external display. My built in display is erratic its working but the screen is so filled with lines different colors that it is un useable. (although you can see some semblance of the desktop). When I plug in any external monitor with any HDMI cable it starts working perfectly. Both the built in monitor and the external monitor. I have tried so many things Ive ran out and resorted to this forum for perhaps a solution. Things like contacting apple, rebooting, firm ware, Os updates to name a few. I have read countless similar problems But Most of the others are the Built in screen is NOT working in any scenario. While mine does with an external connection. I am now looking at the idea of replacing either part LCD LVDS Display Cable or the HDMI /Usb board. Any thoughts would be appreciated :: -Sam
Ouch! In your case the MUX logic within the main logic board is having issues. This is a loading issue where when you connect the external the load needed is present and when you disconnect the external the signals get messed up. Sometimes the issue is within the internal displays T-CON logic.
