The HP 50.0 service error usually indicates a problem with the fuser; although, it can mean there is an issue with the power supply or control circuits. Most of the time, however, it is simply a worn out fuser.
What is a fuser, you ask?
A fuser is a replaceable printer assembly that heats up in order to melt or “fuse” the toner onto paper. It consists of a heated roller or film, a pressure roller, drive gears, and sensors. Because this unit uses heat and pressure during the printing process, it is prone to wearing out.
Turning the printer off to cool down will sometimes eliminate the error message and allow printing to continue, but this will only work for a short time; this is NOT a fix. The 50 error is a warning that you will have a dead printer on hand very soon. At first sight of this error, it would be wise to order a new fuser or maintenance kit. It won’t be long before installation of a new fuser becomes necessary.