Woody, I had a similar instance with my Viking I. Whenever I would switch to the 'Plate' position, I would blow a fuse. When I did it while it was out of the box, I noticed some arcing going on inside the rectifier. Come to find out that over the years, the rubber grommets that protected the posts on the meter deteriorated and it was shorting out over to the 'can cover' of the meter. Also, check that spaghetti around the any and all Johnson transmitters. They are notorious for breaking down and doing the same thing!