Camera Preflashing

Needing some help here.

I've got a 7D and I'm not sure if I've messed with a setting but it has started to pre-flash a lot. The setup is the camera's own flash on manual at its minimum power, a couple of Z240s on manual, and a FIX500 as a focus light.

I'm wondering if the camera's own flash being on 1st or 2nd curtain would make it more or less prone to pre-flash?

All help, and suggestions most welcome.

Cheers

Is the advance canceling circuit on the Z240 on or off?

Have you the red eye reduction function activated?

Could be the autofocus assist also. Need to switch this off.

Thanks for the input guys. A few things to check out.

Great hammerhead. Sorry I forgot to mention it originally. The ACC circuit is engaged. The button is pressed in.

Could be the autofocus assist also. Need to switch this off.

Thanks Alex. This was on. Doh!