[Elecraft] KPA500 no power out

[N7FN at comcast.net]

Can someone advise me on the following?

My KPA500 (S/N 2663) Amplifier stopped working in the middle of a CW QSO on 
7MHz.
It has been working flawlessly for the past two months (since new).

At the time:
Driver is a K3 running 20w and KPA500 running 400 watts.
Antenna tuner is a KAT500.
Antenna is a GAP Challenger.
Frequency was 7.07 MHz.
While transmitting, the SWR on the KPA500 went high and a Fault flashed.
The KPA500 seemed to reset its self and I continued sending.
The sequence repeated a few seconds later except that the KPA500 had no 
output power.
Further testing resulted in the following findings:

Reloaded the firmware.

K3, KPA500 and KAT500 was connected in accordance with Figure 1, Page 5, of 
the Owners manual.
For the following tests, the output of the KPA500 was connected directly to 
the SWR meter and the SWR meter was connected directly to the dummy load 
eliminating the KAT500.

Frequency: 3.57 MHz, All works well.

Frequency: 7.07MHz, K3: (ON) 100w, KPA500: (Standby), SWR on KPA500: 1, SWR 
on SWR meter between KAT500 and dummy load: 1.1:1
    K3 power reduced to 10w, Switch the KPA500 to Operate, KPA500 no lights 
indicating SWR or Power.  K3: SWR and RF indicators jumping up and down. 
Raspy tone heard in station monitor (TS-850).  The LCD shows: "7.0 MHZ" no 
matter which switch around the display I push or how many times I push them 
or how long I hold the switch.

Frequency 14.07 MHz, All works well.

The KPA500 (kit) is under warranty, anyone know what s going on here?  Did I 
do something wrong?  Is it time to send it back to Elecraft?

Frank
N7FN