@mitu finally got it working with a Beta version of retropie, found some great Roms too, thanks for taking the time to help dude 👍🏻

Can you show a listing of the ROM folder on the Pi, where you copied the arcade ROMs ? If they're not in .zip format, then they will not show up.

@grant2258 Hi Grant - yes I think I've realised that this is the problem. The default RetroArch setup creates a virtual gamepad and binds both virtual gamepad and keyboard. I think the problem with Defender is that these mappings overlap - so the virtual gamepad is triggering as well as producing a keypress, and these are both bound to different things (eg thrust AND fire).

Thanks for your help!

@BuZz SOLVED!!! Thank you so much - that worked!!! This also ties in with what @mitu said in respect of the "select" button being mapped to coin. YAY :)