i'm assuming you are asking about the power/AC fuse?
on my 861SE the power fuse is located just below the IEC AC power cord input in a tiny drawer that you have to open using your finger nails.
the 781i probably is the same....
on my 861SE the power fuse is located just below the IEC AC power cord input in a tiny drawer that you have to open using your finger nails.
the 781i probably is the same....