Last week I was called out to work on a HP CM6040 with a light print issue. When I arrived onsite I printed a few test pages and it became obvious that they were having problems with the black toner or image drum.
Today we’ll tackle this light print situation. It is not covered in the service manual and I believe, with the design of the machine, this could easily be a common issue.
The first thing to do when troubleshooting light print issues is to isolate the problem. Is it happening in all colors or just one? To find out, print some test pages; the diagnostic page and print quality (PC) troubleshooting pages are the best for looking at individual colors and comparing them to one another. However, you should also print the configuration, demo, supply usage, and Error Log pages to get a better understanding of what is going on with the machine’s history and usage.
Below is where to find the Print-Quality troubleshooting pages, for example.
Use the built-in print-quality-troubleshooting pages to help diagnose and solve print-quality problems.
1. Scroll to and touch Administration.
2. Scroll to and touch Troubleshooting.
3. Touch PQ Troubleshooting.
4. Touch Print.
In the case of the machine I was working on the test pages showed me that the customer was experiencing light print in the black toner or image unit. All the supplies were at least half full or more and the black toner and drum unit had just been replaced. Also, the error log showed that it was getting 54.14 Errors. This error is not in the service manual but through deduction of similar errors it means the printer is experiencing problems with the black toner sensor output.
I pulled the black drum out and checked the toner sensor window. I noticed that the image unit had no toner in it, which would explain why the machine believed it had a toner sensor issue. The toner cartridge read full but the drum unit was showing that there was no toner in it. So I knew there was a problem with the toner supply getting into the drum unit.
On top of the drum unit, behind the hole where the toner falls into the unit is a white plastic piece with four arms. On the bottom of the toner is another white plastic piece with four arms. When the toner is inserted in the machine the toner cartridge depresses a black piece of plastic around the white plastic arm on the drum unit, unlocking it. The arms on the toner and drum mesh together and it rotates the white arm on the drum unit clockwise, opening the hole on the drum unit so toner can fall in from the toner cartridge.
The white plastic piece on the drum has four arms. Each time the arm is turned it either opens or closes the hole. Somehow, the arm on the drum had been rotated so it was in the open position when the toner was not installed. Therefore, every time the customer installed the toner they were actually closing the hole on the drum, not opening it.
To solve this problem remove the drum unit and check whether the hole opening is open when you remove it from the machine. If so, it is in the wrong position. Press down the black plastic surrounding the white plastic arms and rotate them so the hole is closed. If you need a reference point remove one of the other drum units in the machine to see how they are positioned. Once you have the pieces situated correctly re-install the drum unit into the machine.
This procedure will not fix the light print problem immediately. After re-starting the machine the sides of the image were improving but after a few copies the print quality started to decline again, so I knew I had to get more toner into the drum unit.
While this machine does have motor test that runs the toner motors, unfortunately it doesn’t run for a long period of time like on some other machines. What I ended up doing was running about 4 or 5 full calibrations. In this state the machine is running for a long period of time and running the toner motors. After, the fourth or fifth time the black toner was restored so I ran the calibration one more time to be sure, then put it under some large runs to make sure the quality stayed the same.
After running a few hundred test prints everything seemed to be working the way it should be and the machine was printing consistently with no quality issues. I see this as a potential issue with these machines and I can’t believe I’m the only one that will run it this problem. It’s not included in the service manual as a possible solution to a light print problem. I hope this helps others resolve light print issues.
Kevin Gumpp is a certified printer technician and freelance writer for Market Point. If you have a question regarding this topic or have any other printer repair related questions or topics for which you would like more information, please send an email to firstname.lastname@example.org.