Output volume has dropped in right channel

I first thought the right channel had gone completely dead. After checking, I found out that the channel wasn't completely dead, but the volume had dropped considerably. I have tested the right speaker and speaker-cable on the amplifier's left channel, and then it works fine. I have also removed all the inputs to the amplifier and tried with other inputs. The problem is still there. My conclusion hence is that the problem is in the amplifier. Anybody having any suggestions on what's wrong with my amplifier? Thanks.