Find the connector that is responsible for these solenoids on your power driver board. Have one of the solenoids firing with the coin door shut. Wiggle the connector left and right as well as towards and away from the board, and if the solenoid starts firing, you know its that connector.
This situation happened with me on TAF, and that was how I fixed it. Ended up re-placing the IDC connector with a new Molex connector. Problem has been gone since.
Just reviewed the TAF manual. Coincidentally, my problem was with F105 controlling solenoids #1-8. In my case, I had one of the pop bumpers continually fire while I implemented the procedure above.