uno rev3 - and dfu-programmer

I'm having a problem putting my uno rev3 into dfu mode. I short the reset pins next to the atmega16u2 chip and see the LED flash, go off then come back on.

but when I try to erase the firmware with dfu-programmer I get the response :

dfu-programmer: no device present

All the forum posts I've been to suggest its because I'm not sending the atmega16u2 into DFU mode correctly.

I've tried shorting the pins as I said before and connecting the rst to ground and grounding the capacitor below the tx led as I saw in another forum. but still nothing.

Any help please :slight_smile: