Joystick Issue, Keyboard Unresponsive

[PTherapist]

I've only recently gotten an Amstrad CPC 464, having never previously owned one.
I have several joysticks which all work fine, but I'm having issues with 1 of the ones I prefer to use - a Quickshot II Turbo.  It works fine on my ZX Spectrum (Kempston Interface), as well as on PC via USB adapter.  However, on the Amstrad it causes some weirdness -
When it's connected, the letter Z appears when you switch on the CPC.  Easy to delete this letter and the keyboard works fine etc, until I then load a game.  Once in any game, the keyboard is completely unresponsive until I disconnect the Quickshot II Turbo.
I wonder if anybody has any ideas?

[Bryce]

Hi PTherapist,       

Z is the second fire button (pin 7 of the socket) which is also used as 5V power for joysticks with autofire. Either autofire is enabled or possibly even faulty in that joystick.

Bryce.