[Elecraft] K2 No Side Tone After Firmware Upgrade

[cstoverva at aol.com]

 I just aquired my second K2.  It's and older one with a 3 digit serial number that I purchased used.

Plans are to build and install a KDSP2.  In preparation for that, I upgraded from firmware MCU2.01 / IOC1.02 to MCU2.04 / IOC1.09.
Now I've lost the transmit sidetone.  Toggling between sidetone source U8-4 and U6-25 makes no difference.  Replacing the old firmware restores the sidetone.

What am I missing?  Is there a mod to the control board I need to make?  I haven't been able to locate any info.  Any ideas?

Thanks.

Chuck K4QS