sony cdx gt500u tuner issue

Hi All, I've installed a brand new Sony CDX-GT500U head unit in my 96 VS Commodore and had an issue with the tuner during install. Once I had everything connected and ready to go I turned the ignition and the head unit on and reset it as per the manual. When I turned it back on there was no reception, just static. I turned the unit around to have a look at the back and in doing so, felt the antenna connection click in. At this point the unit turned itself off. So I turned it on again, and it beeped once and switched itself off. I tried switching the ignition off and back on, resetting and disconnecting the antenna remote, all resulting in the same beep and switch off routine. When I unplug the antenna connection from the back of the unit, I am able to play from USB and CD no problem. In short, with the antenna connection in the back of the head unit it continually switches itself off. Without it, CD & USB playback no problem, just no radio. Anyone got any ideas? Thanks, Cheesesailor

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