Yamaha Fifty 112 is fading in and out

[csotolongo]

I'm having issues. After about 10 minutes of playing at low volume the amp volume fades completely out and returns momentarily. I really like this amp and want to fix. Any ideas?

 

[pdf64]

Does it have an fx loop?
If so the switching contact on the return may be dirty.
Try plugging a cable between send and return.

Apart from that, a failing solder joint, especially on a part subject to mechanical stress, eg pot, jack socket, is a likely suspect.