Can't get 1024x768 to output to projector via HDMI

I have a Display Port to HDMI dongle that I am plugging into a projector that has a native resolution of 1024 x 768.

I change the resolution for the external display within display properties on my 11" MBA to 1024 x 768, but the projector (an Epson X10) is still 'seeing' a 1080p input, so the image being projected is surrounded by a black frame. The same happens in mirror mode and extend mode. Even if I change my MBA resolution to 1024 x 768 and mirror the external display as the same resolution, the output of the DisplayPort/HDMI still is recognized by the projector as 1080p.

Has anybody else run into this problem and what is the solution?

Thanks for the help.

 

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Thanks for the reply. So if I understand you correctly, the HDMI output from the MBA will only output a true 1024 x 768 signal if the charger is connected and the screen is closed? That seems odd to me.

With the screen open and no charger connected, I can see an image on the projector, so the signal is getting there, it's just not being received as a 1024 x 768 signal by the projector.