I got this from the Wiki. This may be worth a shot.
"If you think the Instrument input on an Axe-Fx III is faulty, perform this test, courtesy of Fractal Audio ([70]):
"If you think the Instrument input on an Axe-Fx III is faulty, perform this test, courtesy of Fractal Audio ([70]):
- Go to a blank preset.
- Create a chain that connects Input 1 to the RTA block. On a separate row create a chain where the Synth block feeds Output 3.
- Set the Synth Type = Sine, Tracking = Off, Frequency = 1000 Hz.
- Connect an instrument cable from Output 3 (left or right) to the Instrument Input.
- Set the Input 1 / Instrument A/D Input Level (Home->Setup->I/O) to 50%.
- Turn the Out 3 Level knob all the way up.
- The Input 1 yellow LED should be lit. Red should not be lit. Go to the RTA block Config tab. Set Bands to 128, Window to Blackman. Go to the RTA tab. There should be a narrow spike at 1 kHz (three bands). There should be no other bands showing power except maybe a little noise at the highest bands. The spike at 1 kHz should be about 2 1/4 divisions below full-scale."