[Elecraft] KAT-500 Unreliable Tuning

[daveingeb at comcast.net]

Over the past six months my KAT500 autotune function has deteriorated to the point where I am getting frustrated. The KAT tuner is connected to a G5RV via 75' of  RG-8 coax and is fed from a KPA-500 which is fed from a Kenwood TS480. I switch between between barefoot and amplified transmissions. Upon application of a  40 watt tune, the tuner appears to find a suitable solution but when the power is raised to over 100W, the amplifier faults to a high SWR, some bands, but not always repeatable. The antenna and feedline have been inspected and all OK. If I change bands sometimes it works at higher powers and sometimes not. Other times it cannot find a solution on some bands and other bands are OK, low power or amplified. If I cycle the power to the KAT500, it is OK for a while and then it has trouble again. The problem appears intermittent. Wondering if anyone has had this same problem. 
Thanks de dave WB7ELY