[ICOM] 756ProII CI-V problems

[Ed K1EP]

I took a look at a ProII today that was having problems with the CI-V interface.  For some unknown reason, the interface suddenly quit working.  Upon my investigation, I learned that communication to the radio works, although not all the time.  I was able to sometimes change frequency through the CI-V.  Data from the radio does not work and since the program is usually polling the radio and expects a response, I wasn't too concerned about the intermittent data receive situation.  I suspect that something is toast in the micro.  I did a full reset with no change.  Before jumping to conclusions, let me say that I observed the CI-V line on a scope to verify no output.  Further, I probed the line from the micro to the inverter buffer that drives the CI-V output transistor and did not see any data while turning the big knob.  CI-V transceive mode was on.  Other than replacing the main board or the micro, any other suggestions?  Has anyone seen the CI-V port fail in a Pro before (with not else apparently wrong)?