I have a Brother MFC-5890CN Inkjet all in one. I love this printer. It's fast. Good quality and the ADF scanner is great. However, recently I've been having issues with clogged print heads. I've always used Brother ink and leave the printer on at night so it can clean the print heads.
Running a cleaning cycle would sometimes fix the one or more of the colors but still left issues with other colors.
A quick google search indicated the if the cleaning cycle didn't fix it the print heads would have to be replaced. Unlike other brands Brother print heads are not a "consumable" item. Cost of the part is more than I paid for the printer and replacing requires near dis-assembly of the printer. This is a six year old printer so warranty service is not an option.
More digging on the net indicated there should be a sponge (flushing box) on the far right side of the print heads path that absorbs excess ink building up on the print head. It took a few minutes to realize the reason I could not see the sponge was it was covered with glob/layer of semi dried ink roughly the consistency of hot asphalt.
Paper towels and windex (spray the towels not the printer) got most of the ink off and out of the sponge. Once the sponge was relatively clean I folded a small piece of paper towel until i had a square about 6 layers thick. I got this wet with windex and placed over the sponge tucking the edges under the plastic surrounding the sponge.
Close the lid and plug in power. Press the "Ink" button and start a cleaning cycle. Open the printer so you can see the print heads moving (not the scanner lid, the printer). When the print heads move to the far left (over the sponge) unplug power.
Wait about 15 minutes to allow the windex to dissolve the ink on the print head.
Gently move the print head to the far right.
Remove the wet paper towel.
Close the printer.
Press "Ink" "Test Print" "Print Quality"
This will do a cleaning cycle and then print a test pattern. If black or color is not correct indicate and go through the test print again. If you still have issues try the whole process again.
I tried to rush the process and only allowed the print heads to sit over the windex/towels for a few minutes and had to go back and repeat the process. The second test print after the second "soak" showed all nozzles clear.