Stan,
Our service manual page 11-24 specifically states that these boards do not have sounds in conventional.
Something, and I think it is a relay, is preventing the boards from getting to DCS. If I apply 18VAC in the DCS mode, connected to the TIU, the engine goes directly to conventional. Being PS3, there is no audible 'watchdog' signal to listen for. Something is causing it to not go into DCS.