The small belt is the most common cause of the error message "Switch Power Off, Check Pen Path". This message can occur when the small belt has worn down, or even snapped. The small belt is located on the right hand side of the plotter. It drives off the motor, to a double pulley assembly, which in turn drives the pen carriage assembly. Tension is applied to it by the idler puller and tensioner assembly. You may notice your printer sounding noisy as the pen carriage moves, which is an indication that this belt may require replacement.
This part is for the DesignJet 200 220 600 and the more popular 650C. Small belt - Part Number 1500-0855