i was called to fix a canon pc 745 that wasn't feeding correctly. it needed a new feed roller, so i replaced that along with the sep pad assembly. no problem there. however, even before those replacements, the machine would sometimes partially feed, then shut itself off when the paper got to the lower rollers, right before the pcr. not all the time, just sometimes. after the parts replacement and a cleaning, the machine always shuts itself off with the paper at the same place. no error code, nothing. just shuts itself off. i need help!