[Elecraft] KAT500: Won't power on unless I remove the DC power cable and reinsert it ...

[Jim Hooper]

I turn my KAT500 off, and then turn it on first before powering the rest of my K-Line on. 

But two or three times now the following has happened:  when pressing the ON button for the KAT500, nothing happened.   I wiggled the power cable in the socket on the KAT500, nothing happened.  I removed and reinserted the power cable and the KAT500 powered on automatically with my pressing any buttons. 

What might explain this behavior?  

73, 
Hoop
K9QJS 
San Juan Island, WA