[Elecraft] K3 shuts down

[Stephen]

My K3 has worked flawlessly since I got it over a year ago, until 
yesterday. It now shuts down if the power is advanced over 11 watts (pa 
in). The power supply seems to be ok as it runs my TS 850 at 100 watts 
without complaint. I have checked and swapped cables between the K3 and 
my dummy load. I did a reconfiguration. The K3 provides no error 
messages, but the display dims and flickers just before it shuts down.
Am I missing something obvious?
Steve, K5SI