[Elecraft] [K2] Odd "Hi Refl"/high current problem only in TUNE

[Steve Kavanagh]

This one cropped up just today, with no significant change in my home station setup, using a K2/100 on 40m using a low inverted Vee.

Sometimes (typically every other or every third time, but randomly), when pushing (and holding) the tune button with the power set to 11 watts or more, I get a high reflected power message on an antenna which is matched at low power.  The power supply voltage reads about the normal 14V and the ammeter in the power supply is pinned at 25 A (or more) when this happens.  An external SWR meter reads lots of reflected power.  Everything unplugged from the rig except the power cable and the coax to the external SWR meter/antenna tuner/antenna. It's fine on a dummy load.

I'd suspect a simple RF feedback problem, except that with 100 watts of CW everything is perfectly normal.  The problem occurs only when using the tune button around the nominal tune-mode 20 watts, so the external SWR meter reading implies that the PA is probably oscillating at some frequency where the antenna is not matched.  I haven't tried any other bands yet, but since there does seem to be RF feedback involved, I'm not sure they will tell me much of a diagnostic nature.

Any ideas as to what might be happening and how to stop it?

73,
Steve VE3SMA