I got a used studio monitor from guitar center, and it started to blow fuses on start. The weird thing is whenever it is on the 220v setting(im in the us)the light comes on and the fuse doesnt blow, however when i have it set to the 110v setting it ends up blowing fuses on start. Also one time when i had it on the 220v smoke started coming out of the studio monitor but the light was still on and the fuse didnt blow. i opened the monitor and on the amp a rectifier diode was burned the diode probably heated up and caught on the insulation material , i put in a new diode and it still blew fuses on 110v and the 220v was able to power up. oh btw the studio monitor is a krk rokit 5, and i wasnt able to see if music was able to play on the 220v setting.
As a wild guess, I would say you have a problem on the output side of the power transformer. Replace (all) the 2 or 4 diodes that rectify the AC. They are cheap. If you still have problems, check/replace the filter capacitor connected across the rectifying circuit. Parts: mouser, digi-key, jameco
This is a wild assumption that your Rokit uses a simple transformer/diode power supply. If you have an elaborate "switching power supply" you will need a schematic and electronic knowledge.