by RichD » Mon Mar 12, 2018 8:24 pm
There is a thin white wire that connects to the wiper button, the other end goes back to the transistor. If there is an open in that wire the controller will only have full speed when the trigger is pulled all the way. The sensitivity control pot could also cause the problem, sometimes those need a cleaning. The sudden failure points to the wire being broken, the controller will become erratic if the pot is dirty. It is less likely that the pot would fail all together. If the wire checks out OK you could spray some contact cleaner into the pot and work that back and forth a dozen times. If neither of those procedures works you might have to return the controller to Difalco for repair.