K2 s/n 567 has gone deaf to I/O access. It's current for mods. Everything else 
in the radio seems to work fine. VFOs tune, all switch functions appear to 
work, Port is ON, etc. If I connect it to the EC2-mounted KPA100, operating the 
power output knob causes the Low/High Power LEDs to indicate properly. I'm 
guessing that just means the AUX Bus is working, but my problem is probably 
with RXD.

The KIO2 is OK. I swapped it out with the one in my other K2 s/n 6911 and both 
work fine in that rig.

Both K2's are connected to a PC via separate USB converter cables. The 
converters both work and the special USB-K2 cables work with either K2. They 
have been in almost daily use for several months, and worked fine.

I put a scope on Pin 3 of the KIO2 connector and issued a Get command to read a 
VFO, then traced the resulting characters all the way to MCU pin 26. A Set 
command also could be traced from pin 26 back. Lots more characters were 
generated for Set than for Get, so that all looks OK.

I'm stuck as I don't know anything at all about what's happening from the MCU, 
or how to test it, but it looks like it's getting what it needs from the PC. Is 
it the MCU (v. 2.04) itself that is at fault?

I'm nervous about swapping the control board from s/n 6911 even though the 
older K2 board is current on mods. If it's safe to do, I'll try it.

Any help appreciated. This is the first failure of either K2 so no complaints 
from me.

Eric KE6US

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