I have xerox phaser 7400 Fault 940 - Xerox Office Equipment & Supplies

SOURCE: xerox phaser 7400

Remove the tray, first look for a piece of paper that has come out of the tray inside the tray area.
Make sure the rolllers are snapped into place. The easiest way to verify that is to remove another tray and compare them.
Look to see if all the switches and actuators are in place.
Make sure you hear the tray up motor running when you close the tray.
Also inspect the paper tray itself for broken items. Compare it to another tray.

SOURCE: Xerox phaser 7400

There really isnt an easy way to do that.
The transfer belt assembly starts off with a fuse on it to blow immediatly on install, and a counter that is internal so that it will end of life and have to be replaced. It's really not a convience counter but an obsolence counter.

SOURCE: Xerox Phaser 7400

That is caused 99 percent of the time by the fuser.
There is a solid aluminum roll and a silicon rubber ( pressure) roller in the fuser. The pressure roller either developes some flat spots from park ( non running) time and over time heat and use cause it to deform and become out of round. What then happens is when the paper enters the fuser it does so with a slight twist, and the pressure of the fuser, for lack of a better term, Irons in that crease during the fusing process.
Gave the explaination so you would understand what is happening.

SOURCE: I have a Xerox Phaser

That is a motor driver board fault.
May be that board itself, Could be a waste bottle interlock not being made.Possibly the engine control board.

SOURCE: PRINTER ERROR

There is a tiny little magnet that falls off and/or has reportedly been put on backwards (fell off is what happened to me) on the auger assembly. It's near the black auger chute on the end of a shaft. It's tiny--a little bigger than a grain of rice. I had to replace the auger shaft assembly but if you can find the magnet, you can super glue it back on.