USB 3.0 port not working 5k iMac 27"

I use a powered USB 3.0 hub to swap a variety of devices, however some demand a 'directly connected' port.

I keep a usb extension to a single port just for such demands.

This port has ceased to function.

I have connected without the extension, tested with known working devices.

Turned off, then rebooted

Turned off, disconnected power cable, reset SMC re-booted

Rest PRAM as a last resort..

still not working.

this is an appeal to the wider community is there anything else I can try before the Apple Store visit..

Any assistance appreciated