20 Most Recent Brother MFC-9840CDW Laser Printer - Page 9 Questions & Answers

with the front door (toner/ drum door) open press clear/back button then 1 for yes.

Maybe you should clean it :)

Please follow the following steps. 1) Turn off the printer. 2) Shutdown the PC to which the printer is connected.3) Remove the USB/Serial cable through which the printer connects to the PC.5) Now, reconnect the USB/Serial cable and switch ON the PC (only PC and not the printer).6) Let the PC boot up and login to windows.7) Now, switch on the printer, PC should detect the printer automatically now.

I had this problem trying to print from MS Word in a template I downloaded. I found this link and it worked perfectly. I'm using Word 2010 so I had to adjust accordingly. It's for a slightly earlier Brother model but that did not affect my using it.

Hi there,
This can be a print head problem. Clean the print heads carefully and check if this fixes your problem, if not then we might need to change the drum and the charge rollers.

Drum -- A drum cartridge is coated with a photoconductive material that allows electricity to pass when exposed to light. As an example of why this can be the failure, if you leave a drum out in light long enough, you will get dark backgrounds or just black pages. However, drums do wear out over time too; specifically the photo material the drum is coated with. As this degrades, more of the positive electricity on the inside of the drum gets through and grabs toner, as if the laser wrote to every square inch of it. A damaged or defective PC drum can cause black or colored streaks/lines, voids, speckles and various other print quality problems.

Charge Roller - Also known as the BCR or Bias Charge Roll. The charge roller pulls double duty. It energizes the outside of the drum with negative energy and as a result it cleans any previous latent images. If the charge roller were failing to energize either due to the HVPS or the charge roller itself, it wouldn't clean any previous unused toner deposits from the last revolution would start to accumulate and appear on paper more and more causing haze. A missing charge roller causes completely black pages.

Hope this helps

On the TN-155 toner cartridge, a mechanical 'flag gear' that will reset the counter for each individual cartridge when first 'triggered'.
After each page print, the appropriate counters are incremented regardless of toner content (that is why it is still printing 'flawlessly') and after a pre-determined count has been reached, you will get a warning to change the drum as is will then be notionally (not actually) empty.
Before you decide to reset the 'flag gear' on the drum, make sure you are not actually nearing the physical empty state ... it might be a wiser decision to purchase a refill kit which should come with instruction on how to fill and reset the 'flag gear' (this needs some dismantling of the drum cartridge) or buy a compatible or genuine toner drum cartridge.
In any case, Google 'Brother drum flag gear' for more information.
Good luck!