These are just some random notes about symptoms and fixes with the Mfc7300 (and other inkjets in general). The printer is okay, but I can't recommend it because the ink carts are expensive. All inkjets are like that. So, I recommend getting a laser printer, which (in my experience) can last years and years.

Symptom in italics - solution in regular text.

The print is streaky - clean the print heads a couple times. You might want to set up a cart as a cleaning cart with windex in it, and replace each color individually, and clean.

Black (or color) does not print at all, or are streaky in very regular patterns - the electrical contacts connecting the print head to the printer may be off a bit. The connections are made on the left and right side of the print carriage. The contacts themselves are created by sandwiching two sheets of plastic printed circuits together, and clamping them against an array of metal points. All these things need to be clean and aligned just right.

To unclamp the sandwich, first, remove all the ink carts (go into ink replacement mode first, and then unplug the printer.) Then, remove the plastic tray that the carts fit into; there's a little tab on the front to release it. It lifts up and forward. Then, on either side of the carriage, there's a square plastic block that reads "R" or "L" in faint raised letters. Pull up and forward gently, and it'll unclip, and the sandwich will fall apart. Note that the holes in the plastic sheets are spindled onto the small steel pin, which aligns the whole deal. Make sure it all fits together, and replace the clip.

Reinstall the ink, and try again.

Head gets clean, and then gunks up again - it could be bits of dried ink sticking onto the head. Soak a paper towel in windex, and then clean out the head cleaning area. That's over to the right side of the carriage. There's some rubber suction thingies that get grimy with dried ink. Wipe them clean.