How do I manually release the toner cartridge carousel? It is stuck between cartridges and just makes a not so good sounding noise when it tries to advance.

I had a similar problem in that after changing one of the cartridges (I bought a whole set), the message "cannot rotate cartridge" appeared. I tried pressing the cartridge in more firmly and may have caused the carousel to rotate a little in the process. I cycled the power which seemed to clear the error message and allowed me to select the next cartridge to change, but upon opening the door to change it, was unable to remove the old one as it was positioned a little too high. I eventually cleared the problem by manually rotating the carousel by pressing in and holding the carousel release (see arrow) while rotating the carousel downward slightly, to line the cartridge up as it appears in this picture. Then powered it back up and was able to do the normal cartridge replacement procedure for the remaining cartridges without further error messages.

Replace the cartridge.
The gears are the same for all the cartridges.
If it is a new cartridge, try to get it replaced.

On the 2840,one reason why the carousel gets out of alignment is because non HP cartridges were used and they were leaking toner. The leaking toner gets into the carousel gears and causes them to jump a couple of teeth.

If you have a warranty HP will fix the problem under warranty repair. However, if you were using non HP cartridges you will be billed. If your problem is non aligned gears, you won't need parts. The gears will have to be aligned and vacuumed. It doesn't require dismantling the printer.
If you do have to pay, it should only be an hour of labor.

Does it print good? If the printing is good, the carousel isn't out of alignment. Don't fix it if it isn't broke.

HI,
Open the top cover of printer and try to clean up the carousel motor solenoid clutch. There are one foam tape - cean or better replace it.
clean or better replace foam tape. (It is just for make less noise.)
After that control carousel home position left and right gear home position marks must have same position.

You can open the machine and use a pen or screwdriver to press the carousel release. Then rotate the carousel to access the cartridge to be swapped.

To rotate the carousel of the printer and not use the front panel do the following. Remove the drum; place it somewhere away from light. Leave the top open where you removed the drum. Close the front door. By closing the front door, you have depressed the locking mechanism that locks the carousel in place. Now using both your left and right hand and using even pressure, rotate the carousel (from the top of the printer) to the position where the toner is at. If the carousel makes any kind of clicking/grinding noise then it is still being affected by the locking mechanism, I would not suggest continuing. If you do not exert even pressure when rotating it this way, the carousel can become canted (twisted) and then would need to be replaced..

turn off machine,use a large paperclip,straighten out one side,insert paper clip in to slot on right side(white guide next to blue arroe)to deactivate the carousel clutch,this will release the clutch and you should be able to rotate carousel manually.

This worked for me
Each toner cartridge has a small green chip with 3 gold-colored contacts on it. First thing to try is to rub those contacts with an ordinary pencil eraser. You will need to rotate the toner carousel to get to all 4 sets of them. To get it to rotate, there is a little square-ish hole in the white plastic housing to the right of the toner cartridge that is visible when the top cover is raised. Push a pen down in the hole, which will push on a tab allowing you to rotate the toner carousel until you can see the next cartridge. Repeat for all four toner cartridges. Close up the printer, power it up, and see if it solves the problem. If not, do this: Remove the drum (gently pull on the green handle). Be careful not to touch the roller or let it contact anything. Get a flashlight, look down inside the printer on the right (it's kind of hard to see, it's almost under the toner cartridge). You will see a black sensor switch with three wire-like contacts, surrounded by a square white housing. Wipe off those contacts, if you can get the eraser in there better yet. Contacts are kind of flimsy, be VERY careful you do not bend them. Next, take the point of a pencil and push on each contact, it should move in and return when released. If that seems good, put it all back together and try the printer again.

ok, for those who are having troubles releasing the clutch.
when i fixed my printer, i didnt even know there was such a release.

i fixed it in an other way (not for the faint hearted)
open the printer, remove all cartridges and photoconducter unit.

when misalligned, you will notice the guides where the toner cartiridges slide into place, left and right, are shifted.
the part of the printer body guides misalign with the carousel guides.

basically, what you need is a big screwdriver.
push the big screwdriver on the right side between the carousel and the body.
the black plastic ferriswheel will bend inwards, enough to go free from the little white driving gear wheel.
now move the right ferris wheel 1 notch into position.
ready. reinstall toners etc.

be carefull not to break it.
it does work, done it on 3 machines now.

the only reason why this happens which i could find,
is that there was a toner cartridge that is stuck.
feel if you can rotate the white cartridge gear by hand.
if not, that is your problem.

possible lesson:
do not over fill your cartridge.
it is perfectly possible to refill, done that many times with these machines, but dont overfill.
ot maybe it is moist in the toner or something.
these cartridges dont have eternal life

good luck, dj

Open the front door and remove the toner bottle.

Look near the colour toner carts and you will see a small round hole. Jam a screwdriver in that hole and the carousel will rotate freely. Move the carousel round and remove each toner one at a time.