NAC552 Problem - Intermittent Sound

For the last week or so I have found that my NAC552 will only play the CD in channel input intermittently. When the fault occurs, there is a signal in the system but I can only just hear this when I turn the volume up fully. Just a faint sound can be heard. I thought I had fixed this, or it had fixed itself a few days ago when I first noticed this. I re-mapped the 552 inputs, exchanged hi-line for standard IC, powered down for each change and then went t back to Hi-line. After numerous power on/off cycles, the system came back to life. Oddly, the phono input was un-affected and played at normal volumes throughout. This problem seemed to occur after a particularly nasty brown out of the power supply to the house last week.

Anyone else had this issue and any advice? It is a long way back to my local Naim dealer from Athens.

Dave