I've been using the module for several months and am very satisfied -- it sounds great!  However today it appears to be malfunctioning.  I'm getting output but it's VERY low, even at max gain.  The preamp gain pot seems to only produce audible output when it's between 3/4 and fully maxed.  

I removed all the other modules from my rack, and tried this module in several different slots confirmed to be working with other modules.  I checked the setup guide and confirmed all the voltages at the test points.  Where else should I look?  This was working perfectly as of yesterday, so I think something has broken.