can you elaborate on your statement - "all 5 channels, has had low output"? do they all have low output at the same time? Is it intermittent? Have they ever produced strong output?
There are a couple of things that could be simple to fix. 1) are the volume pots on the back of the amp turned all the way up? (forgive me for this one - it's just worth asking cause it's the first thing I would check if I had a problem. 2) Fuses blown - B&K uses internal Rail fuses. Their not hard to replace but you have to open the amp up and be comfortable working inside. Also you need to know how exercise safety around high voltage circuits.
There are a couple of things that could be simple to fix. 1) are the volume pots on the back of the amp turned all the way up? (forgive me for this one - it's just worth asking cause it's the first thing I would check if I had a problem. 2) Fuses blown - B&K uses internal Rail fuses. Their not hard to replace but you have to open the amp up and be comfortable working inside. Also you need to know how exercise safety around high voltage circuits.