[Elecraft] KPA500 will not transmit on 18 MHz

[TG9AJR]

Hi,

Yesterday when trying to work NH8S on 17m CW notice that my KPA500 will not transmit,
just minutes before I worked NH8S on 20m CW with the KPA500, here it is the scenario:

KPA500 will operate normal STDBY and OPER and switch bands in all bands.

But on 17m even on OPER with GREEN LED on if I transmit with my K3 none of the other
LED on power output or SWR will light and off course no power out.

In a couple of occasions I switch from 15m to 17m the frequency display on the KPA500 
will display properly, but when PTT the K3 the KPA500 switch the band display for 30m
or 20m on a couple of test, but still does no power out, then did the same test again but
this time the band did not change and still no power out.

Just wondering if anyone had heard or had this same incident, any leads ?

Thanks and 73 de

Juan
TG9AJR