Have you checked fuses?

One of the best pieces of advice I got about pinball repair was to check the connections and and fuses first, because they're common problem points. On the playfield, it's connections and mechanical alignments. You can spend hours trying to troubleshoot various complex aspects of game only to find out you've got a wire that's come loose, a connector that's not seated tight, etc. More often than not it seems like a simple fix, its just finding what the fix is that's frustrating.