I have a Marantz PM55 SE amp which, although a few years old, has hardly ever been used in anger. The other day it wouldn't switch on so I opened up the case & found the fuse on the PSU board had blown. I replaced the fuse but it blew again as soon as I tried the power. I then replaced the power cord but still the fuses go. Any help would be much appreciated, can't afford to send it for service. I have basic soldering/DVM knowledge....