Walkabout Scout cuts out

Hi all,
I was just about to purchase a WA scout 15" locally after playing it briefly over this past weekend. It was in great shape, little wear and tear, and the seller said it had given zero problems.

However, the amp would cutout, with the master was set to 0, while gain was maxed, and then slowly raising the master vol.

Not that this is a usual setup, none the less it seemed to be an issue.
Does anyone have an idea why this occurs ?