[Elecraft] KAT500 - Tuning Anomoly

[Bill Wiehe]

Up until last week, my KAT500 has run lawlessly. However, it now has a problem tuning my 160M dipole for no obvious reason. Symptoms are continuous searching for a match. If it finds a match in tune mode,  as soon as you hit the key,  it begins tuning again in "Auto" mode or faults in "MAN" mode, regardless of power level.   What is interesting is that the KAT500 will tune my OCF Windom on 160M with no problem. Initially assuming it was the antenna at fault, I did the follow checks.
- Checked the 160M dipole with an Antenna Analyzer and both it and the coax check out fine. Even where the analyzer    suggests a 1:1 match, the KAT500 tries to retune. - Switched input ports on the back of the KAT500. No change.
- Used the K3 ATU (with KAT500 in bypass mode and with the dipole directly connected to the K3) and it matches the   160M  dipole antenna with no trouble. - Erased all the previous 160M tune memories, no change.- Reset factory defaults, no change.- Reloaded the firmware from the website, no change.  
I would appreciate insight one my have.Thanks & 73 Bill - W0BBI