So my Gallien Krueger MB500 has (yet another) problem. Or if I'm to believe what I've read, it's a "feature" and not a problem, i.e. a safety shutdown due to overcurrent/bad cables etc... Scenario: I tried to use the MB500 with a cab belonging to a local venue's backline. The MB500 wouldn't turn on, but instead the power button ring was red for a couple of seconds, and when it tried to turn blue, the cab made a quiet "puff" sound, and then repeated indefinitely... red-blue-puff-red-blue-puff-red-blue-puff... The cab is a rather crappy 8x10 (I think Behringer), which has a custom made switch installed for turning off half of the speakers and switching between 4 and 8 ohms. It didn't matter in which position the switch was. The same cab happened to be borrowed to another venue at another gig and the same thing happened, so it's not a local power issue. The head worked normally before and after trying the 8x10, using my own cabs (two EBS 1x12's) as well as a friend's Ashdown 4x10. I tried two different cables, both of which work fine normally. I also tried both the plug and speakon cab inputs. The 8x10 that didn't work with the MB500 has been played by hundreds of other bands with different heads, and also worked fine with the Hartke HA-something and Markbass Little Mark 250 heads I had to borrow in order to play the shows. Could someone shed some light on what's happening?