Power LED blinking - no sound

The amp. was in repairs twice already, always coming back working, but lasted only for couple of weeks. The first time it burned my left speaker. For some reason the protector IC (uPC1237 - never replaced) did not cut off the speaker outputs. The second time it just stopped working. My front speakers are B&W 605 S2 with active subs.  I measured pin voltages on the IC and there was 23VDC on 2nd pin (output offset detector). I traced the voltage back a bit but could not determine its cause - stopped playing with electronics 12 years ago. I have the service manual plus all ICs data and application sheets but they are not much help as there are no clear fault tracking algorithms.