My Hartke HA4000 was fine through sound check then suddenly seemed to malfunction scant minutes before downbeat Friday. It sounded as if all of the speakers were blown so I figured it must be the amp. Sure enough, when I switched to my backup GK BL600 (migrating all connection cables including AC), the problem went away. When I arrived to prepare for Saturday's show, I noticed the amp power cable had been pulled part way out of the power strip. Apparently, when moving our power strip to access "healthy AC" (according to the club manager) before Friday's show, we may have pulled on it a bit. I pushed it in, switched back to the Hartke and the problem was gone. So my question is this; why would this cause a problem for the Hartke while the GK was unaffected?