Hi,

Judging by the amount of threads/posts on muffs, this seems to be a particular problem with the A-124.
The common cause is that the 14-pin IC marked "4069 usually goes and leads to these issues... it even happened to me.
The chips are easily obtainable and cheap and also easy to replace.... if yours is not still under warranty.

Good luck, it's a great filter aside from this little quirk.