My Getaway blew the U20 a few times took me awhile to find the real cause,
the dissapear post coil winding had rubbed thru the wire varnish making its bracket and post 50v,
I think when the ball was touching the post made the wire ramp 50v and found its way into the switch matrix somehow!!!!
Real Pita it would blow the U20 and the next chip in the line also....
