If you turn up the faulty channel and you can hear nothing, then it could be the pre-amp that's gone, otherwise it could be the power amp. The most common cause is a faulty output transistor. It will be open circuit, not short as that would blow the fuse. Though some amps do have a fuse for each channel. The good news is that the other channel is the same as the bad one. So all readings taken with a multimeter should be the same. So if you find a bad/wrong reading IE one that doesn't match the good channel, you have found the source of the trouble.