[Elecraft] K2 Sidetone Problem

[gearjam]

I have upgraded my firmware to the latest revision. (and replaced the I/O controller). The sidetone is gone. There is no option to change the source, it stays on U8-4 when I tap the display button.
When I put the old IC back, the sidetone returns. My K2 is an older (1644) rig and I don't have the 100 watt option or the the KIO2 option installed. Does anyone have any ideas?

Thanks, Larry