Switch test - see if the little laser beam works if you block it.

Pull fuse for magnet and check with a meter.

LTG : )

It means it's borked.

The optos plug onto a small board below the playfield. Reseat them a couple times. If that fixes it. Next time reflow the solder on the pins the connector plugs onto and plug the connector back on and put a dab of hot glue on it to help hold it.

LTG : )

You can also try cleaning the optos with a qtip and rubbing alcohol.

The symptom you describe is as if something is breaking the beam.

Or power to one or both cut. ( it's a connector issue )

LTG : )

I had this same issue with mine just last week. It turned out to be a broken wire on the opto transmitter (the one shining the red light).

The way this switch works is that the receiver expects to see this red light from the transmitter at all times. When the light path is blocked by the ball this triggers the switch. With your switch showing as 'always on' that means that the receiver isn't 'seeing' the transmitted light. This could either mean the transmitter is broken or the receiver is broken.

Can you see the red light on your transmitter? If not, then there's no power going to it or it's dead. Try the suggestions others have made of unplugging and replugging the connectors that lead from these two optos to the board under the playfield. If you can see the red light shining then in addition to this try cleaning the transmitter and receiver lenses.

The other thing to take note of is if when you unplug and reconnect the little white opto connectors on this board, if the associated indicator LED on this board turns on or off or flickers. This will tell you if the dodgy connection is here or not. If the LED never triggers when you do this then the problem is likely the opto itself.

Have a look at the wires leading to the optos themselves, above the playfield to see if they're broken. Sometimes even if they're not visibly broken the solder joints can be broken so you can 'reflow' the solder joints to fix this (I had to do this to fix my Idol opto, which is the same setup as the Shrunken Head).

Luckily you don't have to disassemble much to reach these optos. Simply remove the Shrunken Head by prying it's neck collar off the tabs on its bracket and you can access the lock nuts and screw heads that hold the plastics. The plastic on the left hand side (transmitter) is under the temple ramp so you'll need to use a very short screwdriver or — what I did — and use a 1/4" screw driver bit with a 1/4" spanner to loosen it then do the rest by hand. With the plastics off you can easily access the two screws that hold each opto unit in place. Take them out and check the wires and reflow the solder and replug them back in to see if you're back in business.