Hp laserjet 2420 printer printing completely black pages

the laser beam is block you need to open the printer and unjammed
since every time you put a toner cartridge there is a fin that moves the cover over the laser or maybe you have a faulty cartridge that the fin is broken

check for yhe printing settings eg print rough or smooth copies

This is either a defect in the cartridge. Or a defect i the fusing unit. Try a different cartridge to see if it goes away. Most all print quality issues on HP's are from the cartridge. If the cartridge does not fix the problem then the fuser film is goin bad. You can replace the fusing unit or find a local guy that can do just the film. Much cheaper. If the line down the side kind of "rubs" off like the toner is loose on the page then it is definately the film.

check the fusing unit in the rear of the printer and check your print cartridge for smudges.

dark background usually means the High Voltage Power Supply is malfunctioning.
replacement only.

This is the test to determine toner or fuser issue.
Print a test page
When you hear the paper feed into the machine open the top to stop the machine
Remove the toner cart.
You should be able to see the page with printing on it. (This is before the page hits the fuser)
If you can see the smudge or marks on the page the problem is most likely the cartridge but NOT the fuser.
If the page is clean the problem is most likely the fuser.
Hope this helps

if fll page is black then innk is smudging

first of all try reinstalling the printer software

then try cleaning the nozzle of the printer

The most likely cause is a faulty toner cartridge, replace it

I think that Odyssey user is right it maybe that the print driver is not compatible with the program you are using goto hp.com or hp.co.uk and download the PCL 5e driver

Hope this helps you
Thanks J

take out cartridge and look at roller on bottom of printer, clean with clean cloth and try, also there is a slit ( or hole on the inside ( put your hand inside and try to touch the top of printer there is a hole there where the images go to the laser clean with clean lint free cloth.