The diverter that stages the "left ball lock" is likely out of alignment just enough to not allow the ball to go where it needs.

This often happens when the coil locks on and is replaced. The assembly is disassembled and put back together slightly off. I'm definitely not saying you did this, just that it's happened to this game in its life and needs to be corrected.

You need to get a camera situated in such a way to catch the diverter trying to stage the ball to see how it's failing. I've also lifted the playfield up above the cabinet to get a look at how the diverter is failing, but this is *very* difficult to do. This is probably the heaviest playfield Williams produced. A couple of 2x4s, and a couple of strong friends to lift the playfield and place the 2x4s will be needed.

The idea is to get a visual on when the diverter is trying to stage the ball to see what needs to happen to align things properly.

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Rob Anthony
Pinball Classics
http://LockWhenLit.com
Quality Board Work - In Home Service
borygard at gmail dot com