Hp 9040 print the paper with the last half of paper so dark and when I open the drum it was so dusted by toner

SOURCE: toner life

ok take the your cardinge to printer repaire
he will guide u what to do

SOURCE: HP P2015 prints horizontal lines across paper

you shuld replace the cleaning blade inside the drum!

SOURCE: HP 2840 Jam in Print Paper Path

There are 2 primary paper sensors. One is the registration sensor where the paper feeds in, the second is associated with the fuser unit.

The first sensor is located under a cover under the transfer unit.
i) Open the door
ii) Lift out the transfer unit (Q3964A)
iii) Locate the black plastic cover plate with a small green flap in the centre. This assembly is directly under where the transfer unit was installed.
iv) There are 2 shiny screws that secure this cover plate. Carefully remove these screws.
v) Lift out the black cover plate by lifting the left section up first which allows the right section to come clear of gears.
vi) Check for paper obstructing the small movable lever under the cover plate.

vii) To reinstall the cover plate, insert the right hand side down first and line up with the mounting holes.

I can supply photos if required.

SOURCE: My printer worked very well until I changed the

Smeared output can result when you refeed a printed page into the printer to make a double-sided page. This happens because the rubber rollers that grip the paper to pull it into the printer can pick up toner from the first side’s printing and smear it. So before replacing parts, this is an easy thing to check. Printing multiple pages consecutively will make the pages print progressively cleaner or you can clean the rollers with rubbing alcohol.

Smeared toner also happens because the nonstick coating on the fusing roller is scratched or has baked-on debris. This can happen if the printer is in a dirty environment especially. If you are comfortable removing the fuser, you can try to clean it with a soft cloth and alcohol, but make sure you let it cool down first!

Finally, if this does not resolve your issue then make sure the fuser is heating; toner that is not heated properly will fall from the page and smear. If the thermostat is bad or the fuser not working properly, you will most likely need to replace the entire fuser assembly. This will be pretty expensive to repair so hopefully it's one of those other issues.

SOURCE: My HP LJ 1020 is making a loud grinding noise when

the problem of your printer is the main drive gear assembly, its located inside if you open the cover on the left side