Boss MT-2 Fades

[AureEntulava]

I've got a Boss MT-2 (Metal Zone) effect pedal. It works fine (for a Metal Zone...) when you first plug into it. However, after some time has passed (varies from a few seconds to 20 minutes), the pedal suddenly fades, and outputs a very low-volume signal. Can anybody diagnose and recommend a fix for this problem?

Thanks!

-Russ