iMac Boots to External Display and Not Primary LCD.

Hello Everyone,

Just completed a repair on a clients 21.5" iMac.

We determined that the GPU was shot via the diagnostic LEDs and proceeded with the repair.

We also transferred data from the old rotational hard drive and added a SSD in place of the optical drive.

Everything went smoothly except... the iMac's original OEM LCD stays black (no power) upon startup and when started with an external monitor connected via display port the Apple logo and loading bar appear on screen #2.

The system loads to about halfway then recognizes the internal LCD and then moves the Apple logo to screen #1.

At one point we had toyed with Command+F2 in order to use target display mode as a diagnostic tool.

Any suggestions as to why the external monitor is recognized as the default monitor??

This isn't detrimental to the functionality of the system but I'd rather not have the client need to use OSX utilities via an external monitor as the only solution.

I'm open to any suggestions you may have.