A common problem that I run into with HP Color LaserJet 3500, 3550, 3700 printers is toner specks running down the paper vertically. This problem is different than periodic dots that show up on the page at defined intervals, otherwise known as repetitive defects. With a repetitive defect, note the color of the dot and measure the distance between the dots. The service manual describes what internal roller is causing the problem and you can simply replace the appropriate part.
Random toner specks can be a little more difficult to diagnose.
Typically, the more you print, the more noticeable and the more frequent the dots. In some instances you won’t even notice the toner specks if you just print one page but they become obvious when printing multiple pages. In most cases random toner specks are caused by a leaking toner recovery seal. Each cartridge has a toner recovery seal on the top of the cartridge right above the drum. The transfer belt assembly also has a toner recovery seal on the bottom of the unit.
To get a good test sample, print the print quality (PQ) troubleshooting pages in diagnostic menu once or twice. Additionally, print a few pages just with black print and a few pages with color. If you don’t see the specks with just black print but you notice specks with the color prints then you likely have a problem with the color cartridge recovery seal. If you notice it in black but not much or not at all with color then you likely have a black cartridge recover seal issue.
The toner recovery seal is a thin Mylar or plastic strip that goes along the surface of the drum or belt that helps collect waste toner. If you open the shutter on the toner cartridge and look right above the drum you will see it. If the seal fails it will have a wavy appearance. Often times you’ll see a buildup of toner in the area and toner leaking down the front of the cartridge or the shutter. In other words, toner leaks on the cartridge seals are pretty obvious through a visual inspection of the front of the cartridge. Once in a while you will get a piece of lint or paper stuck in this area. If it hasn’t been there long then you can gently remove it. If the seal hasn’t been damaged then print will restore to normal. To remove debris from this area use a corner of a piece of paper and slowly work the debris out or towards the edge of the drum. If the seal is bent or wavy, then it’s time to replace the toner.
If you get toner specs on both black and color prints, check the seal on the belt. The seal on the belt is on the bottom of the unit. In order to see this you will have to remove the belt and turn it over. When toner leaks from the toner cartridges the specks on the paper tend to be the color of the toner seal that is leaking. The belt toner seal collects all the colors so the specs will tend to look dark brown or black as it is a mixture of all the colors. Often times if a customer is trying to avoid a service call they will replace the black toner because it looks like the black toner is leaking. When that doesn’t fix the problem, they are unsure what to do next.
Again, if the seal is failing it will appear wavy and have a little toner buildup in the area. When the belt fails it leaks right on the paper as it feeds so if you open a machine and don’t see any obvious toner spillage I would check this area.
Side Note: I replaced a worn out belt the other day with an HP OEM belt. The machine started leaking toner in another area of the page after a few prints. The new belt had a defective toner seal.
Third-party rebuilt toners and compatible cartridges are famous for having these problems on color printers. The seals are extremely thin and have to be gently installed. If you bend it when you install the drum then it is shot. This often gets over looked. I can’t tell you the number of defective cartridges I’ve seen on these particular models related to the toner seals.
Obviously, many more things can cause toner specks. What might fix the problem one time might not fix it the next. In these HP printer models I see this problem more often than not related to the toner recovery seals.
If you have any other advice or have seen other things that cause toner specks to show up on a printed page, please leave a comment below.
Kevin Gumpp is a certified printer technician and freelance writer for Market Point. Market Point is a HP PartsOne Partner selling HP printer parts. 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 email@example.com.