Printronix P-Series Shuttle Motor Start Troubleshooting

Product: P300, P600 

Symptom: Printer powers up, when placed on-line, ribbon turns but there is no shuttle motion

This is generally a problem in or at the ribbon control pcba located in the ribbon deck. The AC power that drives the shuttle motor is routed to the ribbon deck because that same AC is used to run the shuttle cooling fan. When the on-line button is pressed, one logic signal (NSD, generated on the logic B) is responsible for advancing the ribbon, and switching on the AC that drives the cooling fan and the shuttle motor. If when you press on-line the ribbon advances, you know that the logic signal has done its work. The next step is to find out where the open circuit is in the AC.

Many techs assume at this point that the problem is the shuttle motor. These motors are very reliable and rarely fail. The most common failure is either the P1 or P2 connection on the ribbon control pcba. The connectors used at these points are a cheap little MOLEX single wiper contact style which over time can oxidize and go intermittent. Because a rather high current needs to go through this point the voltage drop caused by the oxidation gets hot which accelerates additional oxidation and the eventual failure.

To troubleshoot this failure:
  1: Insure the printer is powered off and un-plugged.
  2: Raise the ribbon deck to the service position.
  3: Leave the ribbon threaded on the hubs.
  4: Remove and inspect and clean the P1 and P2 connections on the ribbon control pcba.
  5: Inspect and clean the contacts inside the connectors on the J1 and J2 connectors on the harness assy.
  6: Reinstall the J1 / P1 connection.
  7: With the ribbon deck still in the service position, turn on the power switch and insure the printer is not in a fault condition (platen is down, there is paper in the printer).
  8: At this point there should be tension on the ribbon and paper feed motor.
  9: Push the on-line button, the ribbon should begin to advance and the ribbon deck fan should start.
10: If the ribbons turn but the fan does not, the problem is an open connection between the ribbon control pcba and the transformer.
11: Check for line voltage at P1 while power is applied (just to verify your fan is OK). If there is no AC and the connections look OK replace the harness.
12: If the fan and ribbon turn normally, power off the printer and connect J2.
13: If the shuttle motor does not turn when power and on-line are re-applied, check the AC voltage at the motor connections on the terminal block between positions 2 and 7.
14: If voltage is not present, replace cable harness.
15: If voltage is present and there is no shuttle motor motion, the shuttle motor or start capacitor is bad.