Brother Laser Printer MFC-7420

Ok I fixed this problem. It has to do with Tension on the rod inside the back cover. Open the back cover and remove it. Then emove the black plastic piece by un hooking it on the left side and pull it down then toward you. You will see a rod attached to it that runs to the right. The right end of the rod has a lever that travels in a slot on the right side of the printer. There is a small spring on the rod. Here lies your problem. There has to be enough tension on this spring to activate a switch in the slot on the right side of the printer. Make sure the spring is installed properly. This is a low tension spring so nothing will come flying out when you remoe it and re install it properly. A piece of paper can dislodge this spring. When you get it apart you can quickly see how it should be put back in. E-mail me if you need further help [email protected]

MY PRINTER ACTUALLY HAD A PAPER JAM BUT IT SAID BACK COVER IS OPEN INSTEAD WHICH SENT ME ON THIS WILD GOOSE CHASE. THE FUNNY THING WAS, I HAD TO REMOVE THE PACKING TAPE THAT THE PRINTER ORIGINALLY CAME WITH JUST TO CHECK IF THE BACK COVER WAS OPEN.
OH BROTHER!

I found no sensors. But upon removing the back door and paper tray, I found that there is an internal (black) tray that is holding in a drum and toner cartridge.
Open this up toward you and find a spring loaded arm that runs from the right side toward the center. In my case this appeared to be bent. As I looked closer there where parts of this arm that were not fully inserted into corresponding gaps on the tray. I removed the screws for this but I don't know if I had to. If you do, be careful not to lose the spring that hooks on the right screw.
There's alot of tension on that arm but I just pushed it back into place. A poor design- a single paper jam knocks it out. Call the manuf. and they act as if buying another $300 printer is your only option. This is the #2 problem on the support site, yet there's no solution.

For me, the spring tension was OK, but the thin rod shifted left by a few millimeters during a paper jam (and thus, did no more cross the optical sensor to the right side wall).
There are marks and windows in the black plastic piece that holds the rod so you can re-position it back in place (just bend it slightly). Just check the sensor is aligned with the rod digit and it's OK.
Anyway thanks to landis1471, as he almost solved my issue.

Open the back cover and pull it out of printer .Inside you will find a black carrier for the paper to deliver it to the top part of the printer . Pull it down and dislodge the left side then pull off the right . On this black carrier is a plastic rod which has a lever to the right . This activates the sensor on the right side of the printer . There is a small spring located on the plastic rod which needs to be re-tensioned as much as you can then put it back in . Replace the black carrier and finally the back door . If your still having problems you may need to find a stronger spring and replace . Good luck :-)

Landis1471


Your solution worked, I tapped the spring in place. It was out of place by a tiny fraction. Thank you!!

gc

Paper was jammed!!!!!!!!!!! Take the jammed paper out and it it will all right!

Another problem is the small rail has a lever that should go through a slot in the middle of the black carriage and may dislodge (sideways from that slot during a paper jam. Once you start looking at the gear referred to above, it is pretty obvious. The whole point is that Brother printers are cheap and somewhat prone to these sorts of problems and it seems this assembly is particularly so. The other problem I have encountered relates to resetting the counter when you change the drum (see elsewhere). Motto of the story: look at the interweb when you get a persistent error message that doesn't make sense.

I found a hammer worked for me, but i have anger management problems so it may not be suitable for you. regards damien

Following paper jam, display showed message "Back Door Open", but it was not. I opened the back door and black tray, being careful not to dislodge spring, saw another sheet of paper not visible from front of printer and removed this. Problem fixed. chloe29

Thanks Landis1471!! You just saved me lotsa bucks and all the hassle of setting up a new MFC.

Cheers

"MY PRINTER ACTUALLY HAD A PAPER JAM BUT IT SAID BACK COVER IS OPEN INSTEAD WHICH SENT ME ON THIS WILD GOOSE CHASE. " - Same here.

What a POSitive company Brother is. Actually, the solution is simple but tricky. There is a little black post sticking out of the bottom of the flimsy cross rail that comes out of its slot on the black plastic piece that it is attached to. This prevents the sensor from going into position when the cover is shut. The sensor is on the right side. I took the gray cover off to see this.

I found a paper stuck towards the back cover which caused this problem

There is a switch that senses the 'Back door' open/ closed state Open the door and locate the switch - are the connectors both in place - if they are and they are of the push on type - pull them off and replace and work back forth a few times see what happens if you still get the message this suggests a switch failure - you could perhaps then short the wires together. Also take a look www.fixyourownprinter.com

It seems to me that the error system is junk and picks up error signals / settings and puts them in a ramdom signal generator.

Try ..

Disconnecting from mains power.
then
Opening / removing every hatch, door, cover or item that you can remove with safety to you and the machine. Include the drum and other odds and sods inside.

Reassemble and re-test.

... a totally untested scheme use at your own risk.

CCIF1024. I also took your advice and it worked perfectly. I just wish that I cam across this site before spending over an hour working on the problem myself.

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