IBM 6400 series Maintenance Manual page 125

Replace the platen open motor if it fails the resistance test.
6. Power on the printer. Press Form Feed and View several times and check that
paper moves in both directions.
Replace the CMX controller board if the platen does not open during
paper reverse.
Randomly misplaced dots
1. Power off the printer. Check the platen gap.
Adjust the platen gap.
2. Remove the paper guide assembly or pedestal top cover. On the left rear wall of
the card cage, make sure the nut which secures the line filter ground line and the
AC In Power Supply cable lead to the ground stud is tight. (See Figure 51, page
287.)
Tighten the nut on the ground stud.
3. Disconnect the AC power cord and check the ground leads for continuity.
Replace the AC power cord if it fails continuity test.
4. Make sure the printer is plugged in to a grounded power outlet. Power up the
printer. Run a print test.
If the problem occurs, replace the hammer bank logic cable.
5. Power up the printer. Run a print test.
If the problem occurs, replace the flash memory and DRAM. Download
the emulation software again.
6. Power up the printer. Run a print test.
If the problem occurs, replace the CMX controller board.
7. Power up the printer. Run a print test.
If the problem occurs, replace the power supply board.
8. Power up the printer. Run a print test.
If the problem occurs, replace the shuttle frame assembly.
Ribbon folding or feed problems
1. Check that both ribbon spools are fully seated on the ribbon hubs and the ribbon
runs between the ribbon mask and hammer bank cover.
Install the ribbon correctly.
Troubleshooting 125