Never owned that game, so couldn't help with sensor adjustments. However, drop targets are operated by solenoids. Sometimes it's as simple as a wee bit of contact cleaner (not WD40 or grease of that kind) on the plunger, where it has been gummed up after years of use. Kind of like working out pots on amplifiers that get gummed up on receivers or guitar amps. If the paper on the coil is burnt or dark looking, then the coil itself needs replacement. Of course, there is always a bad connection issue that could cause this as well, or a bad transistor for the solenoid (though this is less likely). I had a System 1 machine with this problem and, luckily, it was the easier of these options to correct. However, replacing a coil is no big deal either. Just solder one contact at a time, slowly removing the old and inserting the new. Hope this helps some, and I'm sure there could be an addendum to my two cents.