[Elecraft] K2/100 Extreme high Power Out - What did I do?

[Bob Mallory]

Experimenting the other day, I had used my RS232 cable to connect a Icom 
Radio to my PC.  When I reconnected my K2, I forgot to disconnect the 
Icom.  I let smoke out of the K2!.

Everything seemed to work, PC control, receive, etc.  Except on 
Transmit, (with Tune button) with a dummy load I have either '0' out on 
low power or 148 watts on high power, nothing in between.  No modulation 
out.

Before I dig in, any suggestions?  I tried to search for smoked 
components, but nothing obvious.
Why would the RS232 port have an impact on the Transmit circuitry.
Thanks for any suggestions as a starting point.
Bob - KD8HXT