Double printing or offset printing on DesignJet 500 and
DesignJet 800 Plotter models.

With the DesignJet 500 and 800 plotter models occasionally you will get printing that appears to be ghosting otherwise known as off set or double printing of lines and text. This offset printing usually has a few causes. Worn or damaged carriage belt, dirt or debris in the carriage drive motor gear teeth, improperly seated trailing cable or damaged, dirty or malfunctioning drive roller encoder sensor or drive roller encoder.

Follow up:

Please read this entire article before beginning your inspections or repairs!

Take each section one at a time to determine your problem. Make sure to run the calibrations and print test after each step, if you have performed corrective action, to determine if you have solved your particular issue.

Inspect the carriage belt for wear or damage, remember to inspect the entire length of the belt. If the belt is worn, stretched or damaged replace it.
Follow the instructions in the Remove and replace guide (chapter 8) of the service manual to replace either your 24 inch carriage belt or your 42 inch carriage belt.

Helpful hint: only release one end of the encoder strip when replacing the belt. Bad things happen when the encoder is reinstalled upside down (yes it does happen even the most seasoned of pros).

If on inspection the carriage belt is not the issue, inspect the drive motor gear for wear, dirt or debris. The drive motor gear is supposed to have teeth on it that match the teeth on the carriage belt.
If it is dirty or full of debris, clean it with a small bristle brush.
If the carriage drive motor gear is worn smooth or missing teeth then replace it.
This can allow the carriage belt to slip and cause your printing problems.

There has been some advice floating around that ghosting and offset plotting issues are
print head related, very seldom is this the case.

Inspect the encoder strip for damage and dirt. If the encoder strip is damaged or dirty the carriage assembly may not be able to read the encoder strip. In that case the carriage will be feeding false position information to the electronics module. If the encoder strip is dirty clean it with a soft lint free cloth. If the encoder strip is damaged replace it. Helpful hint: when replacing either the 24 inch encoder strip or the 42 inch encoder strip only release one end at a time, match the new strip to the old one and attach as you remove the old one.

Check the seating of the trailing cable at the carriage end. This is usually only an issue if the trailing cable has been removed for repair of another issue. Inspect the length of the cable and pay special attention to the connection point at the carriage end. If the trailing cable is worn or damaged it may need to be replaced. Follow the instructions in Chapter 8 of the service manual to replace either the 24 inch trailing cable or the 42 inch trailing cable, depending on which size plotter you have.

More often than not, the problem is the Drive Roller Encoder sensor. Located in the left end of the plotter the drive roller encoder sensor reads the drive roller encoder and marks the position of the roller. This lets the plotter know how far and in which direction the paper has moved.
There is a Paper Advance Test in Chapter 4 of the service manual that will test the movement and sensors for the paper path.
If the drive roller encoder is damaged or dirty you must clean or replace it. If the drive roller encoder sensor fails then it must be replaced. Follow the steps in Chapter 8 of the service manual to replace the drive roller encoder sensor. Then be sure to run the calibrations once the repair has been completed.

Notice: Be very careful whenever you remove the carriage from the plotter. If you have to, mark the carriage slider rod bushings for left and right side. The bushings can be installed in the wrong sides, but they will allow for slop in the carriage movement when installed backwards. Also whenever servicing, or repairing the plotter be sure to lubricate the slider rods. Friction in the carriage movement path will cause premature wear of the carriage belt and carriage belt drive motor.

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# Kieth Garner on 10/19/11 at 12:27
awesome post!
# Printing Freak on 12/14/11 at 21:22
Very important as we found out. Check the entire length of the carriage belt. It may look good, but can sometimes be a little stretched. They're cheap. Just replace it if you are unsure.

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Do it yourself repair information for your HP DesignJet Plotter.



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