Image Defects in Black and White Printers and Copiers

I get a lot of calls from customers who have image defects on their laser printers and copiers.  After about 20 years of experience servicing lasers there is one thing true about 95% of the time: It’s the imaging cartridge!

COPIERS: The first thing to do is eliminate the scanner as the source of the defect. Do this by printing (not copying) something from your computer or from the machine menu or a received fax, making sure you are not involving the scanner. If you still have the defect, then the problem is in the printer part of the copier. If not, then the scanner is the problem and, unless there is dirt on the scanner glass, will probably require service.

PRINTERS AND COPIERS THAT DO NOT HAVE A SCANNER PROBLEM: What is an imaging cartridge? For HP printers it is the toner cartridge. Almost all Hewlett Packard, Canon, Lexmark and Samsung consumer printers and copiers use a single toner cartridge. Brother has a 2 part cartridge: the base(the larger part that the toner cartridge sits in)  is the drum unit. The toner/developer cartridge is the part that is removable.. This is usually just called the toner cartridge. For brother machines, if the print defect is light/spotty print or has marks that repeat about every 1.5 inches, replace the toner cart first. If you are getting defects repeating at about every 3 or  4 inches, remove the toner cart and replace the drum. Reinstall the toner cart in the new drum. (Note: it is a good idea to reset the drum counter, a sometimes arcane  process that varies between machines. The procedure is usually in the user manual. If not, you can call or email for the exact procedure).

Sharp nearly always separates the drum and the toner/developer units.


A typical imaging cartridge is composed of a drum, a developer assembly and a toner supply, 3 essential items for a laser product to work. Now for those of you owning HP lasers, you only know about the “toner cartridge” so where are the other 2 assemblies? Calling an HP cartridge a “toner cartridge” is actually a misnomer: it really contains all 3 assemblies in 1! So, if you have an hp laser, 95% of the time, it is the “toner cartridge”.

Now, what about printers that have separate assemblies such as the Brother laser printers?

When you remove toner cartridge in a Brother printer, the assembly you are holding is actually the drum assembly with the toner mounted in it. So, 95% of the time, if you have a print defect, it will be the drum. Keep the toner and put it into the new drum. Do you get feeling like something is missing? Remember when I said that lasers require 3 assemblies to create an image? So, where is the developer assembly in a Brother imaging unit? Give up? The so-called “toner” you are replacing is actually a combined toner-developer assembly.

Some manufacturer’s like Xerox and Panasonic have all 3 assemblies separate, mostly on their older machines. The  drum is the 9 to 12” wide roller that is usually green or brown. Be careful not to nick or scratch this drum, or you will get a spot repeating every 3 to 4 inches.

Imaging cartridges cause most of the image defects on laser printers. Just because you replaced it 2 weeks ago, it still must be suspect if a defect appears. If you happen to have the old cartridge, stick it back in. Even if it has it’s own defect, if the defect is different than the one you had, then is new cartridge that is defective. It is a good idea to keep a used cartridge for just such diagnosis.

Defects other than the imaging cartridge: I save that discussion for my next blog or “How to do a Half Test”.

If you need additional assistance, you can always call or email me.

John Scudder