[Elecraft] K3 (not S) Antenna tuner strangeness

[g3pqa at onetel.com]

Guys,
I've run into something on 80M trying to use the internal antenna tuner.
It fails to tune to a low SWR. Brian K3KOI had a similar problem but never quite got to the bottom of it because partly intermittent, possibly multiple faults.
In the end to fix it:-  
a) I rewound one of the swr sensor toroids (centre wire had possibly arced to ferrite because I disconnected antenna by mistake and tuned), and 
b) fixed a new earthing wire between KAT3 chassis and SO259 Ant1 socket body. (possible poor earth connection via KAT3 securing pillar to side panel) 
John G3PQA