Troubleshooting Hafler Iris Preamp

[timthedog]

My Hafler Iris Preamp just died and I would like to repair it myself. I have a circuit schematic but only a VOM. Suggestions on how to proceed with troubleshooting and repair this solid state unit would be much appreciated. Here is what happened:
On power-up there seemed to have been a brief zap sound; it was hard to tell whether it came from the speakers or from inside the preamp case. Now the preamp still lights up and will pass a signal on both stereo channels. However, only musical peaks make any sound at all and what does sound is very attenuated, clipped, and distorted. The selection of input jack and the setting of the input selection buttons have no effect. For example, plugging a signal source into the CD jack produces this output when the input selection is set to CD, tuner, aux, or to any of the other inputs. The same result occurs when the signal is plugged into the tuner jack or into one of the other inputs. The volume and balance controls seem to work both locally and on the remote. A visual inspection of the printed circuit board shows nothing amiss, there is no unusual smell, and gently tapping on each discrete component has no effect. Internal B+ voltage is a steady 16v. The problem is with the preamp; the rest of my systems works normally.
Jim Gregory