fix all brands of roll laminating machines for a living. As another posted the sensor transistor has failed. Easier access by pulling power plug from wall:( removing end covers, removing 2 screws that allow the back panel to fall open, remove the bottom film idler bar, its spring loaded its in front of machine directly under bottom orange roller. the 2 screws behind the idler roller hold the spring loaded assembly together. the small plug assembly contains a LM 135 precision temp sensor transistor around 12 bucks from digi key. or you can buy that small temp sensor board for just under 300 bucks from GBC:( remove the brass plate to access the transistor.
this generally fixes the always ready machines, the other failure has the machine overheat and take out the thermal fuse, the heavy wired thing on the spring loaded assembly.
replacing the spring loaded bracket is easiest with a helper, to line up the screws. you cant see both sides of the machine at the same time.
this must be the most common gbc 4250 failure recently, this issue comes up often here
bob haller service and sales pittsburgh pa 412 366 4906
December 2011