On the GP680 european version of the HT1250, the 3 amp surface mounted fuse is on the underside of the board, you have to unscrew board from metal chassis, look close to the +ve battery connector is the small fuse, sometimes blue in colour. The board layout and components vary depending on the age as they changed layout slightly over the years. Hopefully the HT1250 is the same. Marked as F501 on the board.
If the fuse has not blown then sometimes resoldering the volume/on-off pot soldered connectors restores power....sometimes the supply goes bad betwen fuse and on-off switch due to multi layer board connector failure so a wire link between fuse and on-off connector proves this (marked 4 and 5 on image)
Pic attached higlighting the fuse. Hope this helps..