Quoted from Maurice:The original switches do work, but a high speed ball is not registered every time. Only 50% registers and those are the slower shots. And two switches need to register, otherwise the shot doesn’t count.
Heighway went bankrupt. Schematics or tech charts don’t exist unfortunately.
Any chance a filter cap could help like on old Bally games? No idea but just a thought since that was something they did for fast shots.