Had system for years with no trouble. Lost all radio presets recently and unit will not hold them for more than a couple of days when power is off. I've moved house a few times and have been on numerous 2-week holidays when powered off, with no trouble. Have to switch power off as I've got a sub-woofer wired into the system and am unable to reach it's on/off switch as it is hidden from view behind the TV etc. Any ideas? Could it be a burnt-out EEPROM?