[Elecraft] Sudden jump in SWR when power above 80 watts

[Ken]

I am having trouble with my K3 tuner, the SWR jumps high when I turn it above 80 watts on 80m.  

At first I thought it was something outside but after replacing open wire feedline, balun, coax, I have come to the conclusion that the problem must be internal to the K3.  

The antenna is a 130' center fed dipole, fed with 45' of open wire to a 4:1 balun and then to the K3.   It tunes easily and works okay on all the bands but on 80m, when I up the power above about 80 watts, the SWR jumps up and the K3 shuts down with "HI SWR.   

The problem does not happen with my old TS-440, nor does it happen when I bypass the internal K3 tuner and use an external Palstar AT2K tuner.

I don't believe I had this problem when I bought the K3 last December but then I might not have run the power up all the way either. 

Thoughts?  Am I missing something?    Has anyone else had this same problem?  

Another thing I noticed (is it related?) is that when I tune the Palstar to 1:1 SWR, the K3 shows a 2+:1 SWR.  If I use the K3 meter to tune the Palstar tuner, then the Palstar meter indicates a 2:1 SWR.  

Thanks,

Ken WA8JXM