Had the exactly the same issue with mine and the solution eluded me for a while as all the switches were reporting when asserted in switch test but the game would not start.
Replaced the game roms and tried the start button and.....IT WORKED!
Rebooted it again and tried the start button, no go.
Put in in switch test again and investigated more closely the trough switches as this game will not start unless it sees 2 balls in the trough.
Asserted the trough switch closest to the shooter lane in switch test and wiggled the wiring to it....no change.
Wiggled the diode across this switch....IT CHANGED STATE.
Re-soldering a not so obvious cold solder joint at one end of the diode at switch lug was the fix.
Pressed out many games afterward to test: Start issue resolved