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John, Computer Science Engineer
Category: Printers
Satisfied Customers: 5077
Experience:  CompTIA A+ & Microsoft Certified Professional with 15 years of experience repairing computers and printers.
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I have a brother MFC-9840CDW an got the following problem.

Customer Question

I have a brother MFC-9840CDW an got the following problem. The colors magenta and yellow are faded. But I detected a way to solve the problem for one print job. In the maintenance mode I use mode 83 and start the Bias Voltage Correction. This works and the voltages for bias are for all colors over 300V. Then the print is ok. After a while the bias voltage for yellow and for magenta are falling to values near 200V. Then the prints are bad. Have You any idea, how to solve the problem permanently. The drum is new. The toner cartriges also. All is reset.
Thank You in advance.
Submitted: 1 year ago.
Category: Printers
Expert:  Freddy M. replied 1 year ago.
Hi my name is***** am sorry to hear you are having this problem. How old is your printer? Has anything been replaced on it?
Customer: replied 1 year ago.
The printer is over 6 years old. The only part I replaced a few month ago was the drum unit.
Expert:  Freddy M. replied 1 year ago.
Have any other parts been replaced within the machines life span?
Customer: replied 1 year ago.
The waste toner box. The printer has printed nearly 21000 pages, mostly text.
Another information: The automatic color registration fails last time I do it.
Expert:  Freddy M. replied 1 year ago.
Has anything else ever been replaced like the drum and fuser?
Customer: replied 1 year ago.
As I wrote above, the drum unit was replaced a few month ago (I think November 2015). The fuser is original.
Expert:  Freddy M. replied 1 year ago.
I am not sure how I missed that thank you for clarifying. Normally what you are describing is caused by a failing drum. But with the voltage issue it can also be caused by the fuser failing and needing to be replaced. Do you happen to still have a warranty on the machine?
Customer: replied 1 year ago.
There is no waranty on the machine. And I did not think that the fuser is the problem, because the other colors (black, cyan) are printed perfect. And if I print the page for the manual registration, the colors are good. I think, in this mode the bias is set to maximum. Is the fuser different for each color ?
Expert:  Freddy M. replied 1 year ago.
The voltage on the fuser is different yes. They also normally only last 2-3 years before needing to be replaced.
Customer: replied 1 year ago.
Oh, OK !
Is it possible, to test the function of the fuser in maintenance mode ?
Expert:  Freddy M. replied 1 year ago.
Unfortunately the only way to really test the fuser is to try another one. There is no maintenance mode test for it like there would be for life end on other parts.
Customer: replied 1 year ago.
Ok, then I must order another fuser unit. This will last a few days. Then I will contact you. Is this ok ?
Expert:  Freddy M. replied 1 year ago.
No problem you can get back to me by going to and look under my questions. As long as you reply here you should not be charged again and this question should not expire or anything like that.
Customer: replied 1 year ago.
Ok. Thank You so far and Good Bye.
Expert:  Freddy M. replied 1 year ago.
You're welcome.
Customer: replied 1 year ago.
I have now installed the new fuser unit. The result is the same as before. Any other suggestions ?
Expert:  Freddy M. replied 1 year ago.
That is not a good sign that would normally indicate a board failure. How old is the machine? Did you happen to get an extended warranty?
Customer: replied 1 year ago.
The machine is over 6 years old. No warranty available. Why a board failure ? Is it possible, that it could be a connection problem from the board to the drum or fuser ?
Expert:  Freddy M. replied 1 year ago.
Yes to the fuser but the connection should be integrated onto a board so to replace those contacts you need to replace that board. Most machines try to use as few cables as possible between parts. The power supply PCB would be the next part to test. You can test the caps resistors etc on the board with a voltmeter. They should say on them what the proper voltage is.
Customer: replied 1 year ago.
OK, I will try to test these parts. Is the power supply board easy to test or must I dismantle the whole printer ? Is this procedure described in the service manual ?
Expert:  Freddy M. replied 1 year ago.
I do not have a service manual for this model but I am not sure. However most require you to dismantle the entire machine.