My friend has a 422b, black face - manufactured in 2006. He was operating a net for around an hour. He heard what he described as the positive and negative on a car battery terminals coming together. The amp went dead. Some details... Runs on 220v Everything was fine prior to the "pop" The fuse blown is on the black line, the holder that is close to the side of the unit. The other side does not blow. When you install the new fuse, it immediately blows. He was instructed by some one experienced to do resistance checks on the transformer and the checks show ok. So what do you experts think?