Hi Zoog

> I've managed to wire up the CLOCK and RESET plugs from the A-190 to a
> 5 DIN SYNC plug and have plugged it into my old Korg DDM-110.

You are missing the Start/Stop connection. I don't have a A-190, but it
looks like the A-190 does not provide this signal.

Try a MSY2 or other MIDI2Sync devices like Mungo Sync2, SBX-10, ...

Florian