TV (monitor) doesn't support login screen resolution on HDMI

I have a HTPC/file server with display problems. All my hardware is in my profile, so I won't repeat it other than to say it's an older 720p TV with a single HDMI input. It supports 720p (native resolution) and 1080i inputs on HDMI.

If I boot with just the TV plugged in via HDMI I never see anything on the screen.

To get it to work, I plug in a VGA monitor and unplug the HDMI cable. Once I'm booted up and logged in, I plug in the HDMI cable and run the Catalyst Control Center. It detects the HDMI connection, switches it on, and switches the VGA display off. I then put away the VGA monitor and try to neither logout or reboot for as long as possible. If I logout, I'll often see a scrambled/static display on the screen

This has been a big pain for many months now and any help is greatly appreciated.

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