I installed a new cartridge for a Laserjet 2300 and it keeps printing with dark horizontal lines. How can I fix it?

Did the dark lines start after the change? If so, maybe the drum on one of the cartridges is damaged. (Since you mentioned dark, I'd suspect the black cartridge.) Try replacing cartridges.

If that doesn't fix it, you can send it in for repair if it's under warranty. If it's outside warranty, I'd probably just replace it, unless you want to learn a lot about the innards of a laser printer.

Hi,

Check your Toner, and also the thermal roller of the printer..

Thank you

Black horizontal lines ( page is held Portrait ) ,
where print is affected the print image fails to show behind Line effect but shows in between-
the drum surface has been damaged ( likely wear and tear) and can no longer maintain an even layer of electrons due to leakage/short
solution:
replace the toner cartridge which houses the drum.

that print head is clogged,
do the clean cycle shown in the manual;
new cartridge time if cleaning does not work.
all things work last week but now.
nothing new here and for sure pesky printers
and for sure not used every day. (this keep them going more reliably)
made back in 2008, so is getting long in tooth and on most this full cleaning of the whole printer is advised. ever do that?
per manual?
rtm?
https://support.hp.com/us-en/product/hp-color-laserjet-3800-printer-series/500934/manuals

Replace transfer roller & check..As well as check teflon sleeve surface for any toner particles deposited on it..

This is coming from the toner cartridge. Replacing the cartridge will fix this issue at leat 95% of the time. This problem is caused by a defect or damage to the drum in the toner cartridge. If you have a new spare then just swap them out. If you do not have a spare even an old empty cartridge can be installed to verify that the cartridge swap will resolve the problem.
Good Luck and Thank You for using Fixya.
Wheatland Services

Put the old cartridge back in. Print a page. If the lines go away, get another cartridge.

Does this happen both when copying and printing?
For printing solution, try another toner cartridge.
If lines continue to appear when copying (primarily through the automatic feeder) then lift the auto feeder, and clean the glass -mainly the narrow piece on the left side.

please rate solution :)

There good printers its just who you use to get the cartridges from. We sell some but there not refills and we have good prices if your interested.

Unlike Ghana our can be returned if they don't work.

Change toner cartridges again