Hi, I have an old Sony AV receiver model STRDE 875. When you power up this receiver there is a slight delay and then you hear a click (indicating some relays are kicking in) then you hear the sound streaming from the speakers depending on the number of speakers connected and setting of the receiver. The problem I am facing of late is that the receiver intermittently switches off the centre speaker. YOu hear a click as if the relay is deactivating and then the speaker is off (the speaker is still set at ON on the settings). What can be the problem? The relays? Where can I fix the unit?