You'll have to check what switches send power to the player unit advance solenoid. As I recall there are a few score motor switches and the trough switch in the player unit advance solenoid circuit. I'd first check the trough switch to make sure the contact points are clean and adjusted properly. Do you have a schematic for the machine? This will tell us what score motor switches are in the circuit...

Hi electricsquirrel, fred +
maybe a problem with the player-unit-advance-solenoid.
From the text, post-1 I take: Problem may show up - when showing up ONLY on FIRST ball. This makes me believe and ask "problem on DX-First-Ball-Relay ?".

Look here http://www.pinrepair.com/em/index3.htm#axrelayvideo - start the video - in the short period of time "1:34 - 1:42" he shows the two moving directions and the "stable states" after a movement.
I believe Your DX-Relay works fine - mechanically. I believe ONE of the two coils mounted does SOMETIMES not get electricity to the coil (to pull-in).

Want to verify my theory ? When You have a game You can happily play till "Game-Over" - then look at the DX-Relay - see the "state it is in" --- start a new game and WATCH the DX-Relay. At some time in the Start-up-Procedure the DX-Relay will move (and stay in the new position*+*+*).

OK - play some games - when You have the nonpleasing "stays on first ball": Look at the DX-Relay --- question: Is it in position*+*+*.
IF (if) You say "Yes - it is in position*+*+*": We must look in the path to activate its coil.
IF (if) You say "No - it is not in position*+*+*": We must look on switches on DX-Relay (maybe a wire has broken-off and sometimes has contact - sometimes no contact. Greetings Rolf

Try moving the bakelight if that's what it's called forward or back make sure the points are on individual contacts had the same problem

Check a switch on P if its doing it on all players.