Typically on BSD I've seen misalignment of the across the playfield optos (or they're just dead), the opto board has failed (replacements are available), or the coiled cord under the playfield that supplies power to the magnet has a broken wire (very common because it's moving all the time).
I would check the playfield optos first, then do a continuity check on each of the wires in the coiled cord. Make sure you move the harness around a little to simulate like it's moving when you're doing the continuity test.
ANy of these three problems are very easy to fix, and most people shy away from buying one of these if the mist option is working.
Good luck.
Omaha, NE
