After going thru all the hints in the book, we discovered that there was a wire break or short in the Canterbury wireless unit on the back wall of the house. Replaced the box with one from another machine and the problem stopped. Sent the box to Bob Schultz for repair and no problems since its return. Just another possibility to check.
acss, check the brake spring. It is on the bottom of the brake, (black rubber strip on the back of the machine). They tend to break off. The brake temporarily slows down the throw arm, without that spring the machine will tend to, "windmill", and keep launching targets one after another. Seen this happen on Our Pat traps. Hope this helps.