DIMINISHED POWER OUTPET ON HI SETTING WITH FTM 400XDR

[ve3kmq]

My 15 month old FTM 400 radio now only gives me 18 to 23 watts out on the HI setting both on 2 meters and 440. I monitor with a Daiwa CN 901V cross needle meter. Up until now it has measured at or close to rated output of 50 watts. The other power setting of MED and LO  are also lower but not as drastic (14 to 18w and 3.2 to 4w, respectively). All measurements were made with a dummy load and two different antennas (Comet GP6 and Cushcraft 124WB 2 meter beam). I have done a full reset to the radio and the problem still exists.

I have seen this with past radios I've had (Kenwood V71) where after several years of use the HI power setting would yield well below rated power.

What's happening and how can I remedy this problem on my FTM 400?

Thanks

Mike

VE3KMQ