Usual suspects, even though only 2 years old probably. But final straw was mains fuse blowing at switch on, no major problems on previous use. Consumption max 100mA rating plate says and 1.6A antisurge for 115V use and
630mA antisurge for here , 230V use , toroidal transformer. Owner did not chuck the fuse and it is only just blown , ie just a small patch of slight spray of white dust/smoke on the glass at the break so little more than mechanical failure. Assuming nothing else found after taking the amp to bits , replace with 630mA and advise the owner to be prepared to change the fuse every year or so ? , or uprate to 800mA antisurge. Methinking 500mA to 630mA is not enough margin for toroidal and normal switch on surge, no thermistor in schematic or actual, schematic that I have shows 830mA for the 1995 version.Incidentally the loud thumping noise in these , on movement , is the springlines knocking the cardboard closure and the cardboard acts as a speaker cone. They do not bang against the metal side. Will cover with something softer and perhaps add some spacers
-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on
formatting link