I had to replace the plunger in the VUK under the skull and after reinstalling the assembly my drop target no longer works properly. It resets at the end of each ball most of the time, but sometimes not. After resetting, when a ball hits it the target instantly drops as it should, but there is no "lock sequence engaged" or "load the cannon" announcement as expected. Do I have a mechanical problem with the drop target mechanism or did I somehow mess up a switch on it? The VUK is working properly, after a ball lands under the skull the cannon firing sequence begins....

OK, using the switch edge test I determined that in fact one of the terminals on the microswitch had an intermittent connection. I just reheated it with the trusty soldering iron and the switch works reliably every time. As an added bonus, I realized that the tab on the lower end of the drop target solenoid armature was loose--this is the tab with a finger sticking out on one side to drag the drop target up when the solenoid is energized. After tightening the nut that holds it to the armature, the drop target resets reliably every time. It's just a source of utter amazement to me that after 30 years and probably thousands of games this thing still works as designed. Miracle from Chicago....