The Flex has never done this before. I just added a 4/1 unun to my 33 ft. vertical. I had been using a 9/1 unun that worked well. I decided to go with a better unun for a vertical. Trying out 40 meters worked well until I turned on my amp. Then I went to tune and hitting the tune button would not turn it off. As soon as I turned off the amp the tune button worked. Did it in 20 meters as well. I haven't tried other bands yet. Any one with a suggestion as to why this is happening would be welcomed. I tune with less than 15% power. Transmitting too much power on tune? Something wrong with the amp? It's a Tokyo HY-POWER HL-550 FX that has worked flawlessly. LDG AT-600pro Tuner. Balun Designs 5K 4/1 unun. Thanks.