The cause is unknown, possibly a vacuum tube issue, but the volume occasionally decreases or becomes distorted, so I'm offering it at a lower price than usual. Those planning to use it professionally, such as for live performances, may need to have it repaired. Please consider this before purchasing. I was using it until recently, so basic operations are fine, but I haven't confirmed all functions. Please understand this. Also, I'm selling it as-is, with no returns accepted. Please refrain from purchasing if you are sensitive to used items. * Accessories are as shown in the photos. * The volume occasionally decreases or becomes distorted. * Rack case included.