"Brother Printer, the ink tank has ink, all colors (B, C, Y, and M), but why can't it print black?" The other colors are okay."

 There are a few things you can try to repair your Brother printer if it's not printing black:

1. Check the ink levels: Make sure the black ink cartridge is not empty and that there is enough ink to print.

2. Clean the print head: You can try cleaning the print head to remove any clogs or debris that may be preventing the black ink from flowing.

3. Check the print settings: Make sure the black ink is selected as the default for printing in your printer settings.

4. Check the paper type: Some papers have a special coating that can cause the black ink to smudge.

5. Try a different black ink cartridge: If the cartridge is low or empty, try installing a new one, also check that you are using a genuine Brother ink cartridge

6. Run Printer troubleshooter: You can also run the troubleshooter built into your computer's operating system to check for any issues with the printer.

If none of the above steps work, it's possible that the print head of your Brother printer is damaged, which will require a professional repair or replacement.

Advanced Repair

"This is the solution:

1. Find a tissue;
2. Get a bucket;
3. Fill it with warm water, halfway;
4. Remove the cartridge from the printer;
5. Dip the cartridge head in the warm water;
6. Rub the head while it is dipped in the warm water;
7. Remove the cartridge from the water;
8. Repeat steps 5 - 7;
9. Wipe the flex of the cartridge with the tissue;
10. Wipe the head with the tissue;
11. Reinstall the cartridge in the printer, and test to see if it is now working properly."