Been a while since ive worked on a WMS EM but ill see if I can assist..
If I have read correctly... you can add credits as normal but START button does nothing... LOCK relay is latched.
Firstly... motor turning half turn or 1 full turn on coin switch is normal.. it has latched your credit and now waits for you to start the game.
Make sure all contacts on LOCK relay are as they should be when activated.
When you press START it goes through the Credit Unit ZERO position switch... make sure these contacts are touching.. use a DMM You should see the credit go down one if this is working
.. also Ball Count ZERO postion and 2nd COIN relay... if the credit wheel goes down by one then all ive written so far is working correctly... if not... you have a fault on one or more of these relays... OR.. START switch is dirty.. could be as simple as that
