if it's not this (fuse),
http://www.mrmunsell.com/EMPEG/Fuse_Replacement/fuse_replacement.html

nor this,
there might be a loose screw or wire fragment floating around.

then it's this,
a power supply within the empeg is going out or getting loaded too much. i.e. turning up the brightness of the display uses more power and a power supply can't keep up causing dips in the power rails. for this you will have to send it in.

you could try swapping the display boards to isolate wether its the display board or the main board. fyi, the (high voltage) power supply for the display is located on the display board itself.

-vance-
woohoo, my first post.