If you haven't already, double-check your T1 against the switch diagram in the manual to make sure you don't have an errant switch closure or open opto at start up.
EDIT PS--if nothing shows, put the game in T1 test mode for an hour within ear-shot and listen for any flaky switches registering intermittently; last switch opening or closing will of course reveal the culprit on the display.
GL.
Post edited by NM: Edit with additional suggestion.