Fabio,
I think this is of lower likelihood than a failed bridge rectifier but worth a mention. Normally the low voltage regulators would current limit before the line fuse would blow but I have seen a small number of cases where the series pass transistor develops a collector-emitter short, the output voltage goes high and current limting is no longer effective. Coincidentally the last time I saw this was on a 7623A where the +5V supply went to +10V and caused failure of three 74xx TTL ICs on the storage control board. If the +15V goes high there are two tantalum capacitors on the vertical amplifier board that are rated at only 20V and will very probably fail. There may of coure be other tantalum caps with similarly small voltage margins on other power rails.
Regards,
Roger
