ARP Omni 2 - Stuck note

[Andy]

Hi all, 

My Omni 2 has developed a fault. If I hold down a chord, after a few seconds
another note (A3) fades in even with the Attack slider fully left (fast
attack). I've checked the keyboard contacts and none of them are caught on
the buss. I presume it could be the Capacitor/Diode gate for that note that
is at fault.
Have any techies out there got a clue what could be wrong?

Andy.
syntech at u-boat.co.uk