Hi Camru, I wondering if the jam light is on at power up before data is sent to your machine or if it occurs after a print job is sent to it?
If it is on constant ie before a print is sent to it, then we have a sensor or paper detect switch activated. If this is the case then it can be a piece of paper or a remaining fragment of paper holding down the switch or the switch arm itself is broken or its corresponding light sencing photocell is covered in toner/dust.
In Printers there are a number of these sensors in the paper path, generally we have one that detects paper at cassette and bypass position, another at registration roller another at fuser exit, the machine monitiors these switchs for activation to tell if a jam is present. These switchs are tiny plastic arms that get pushed down when paper passes them which in turn blocks the photocell sencing light. One normally finds fragments of paper sticking the arm down, or the arm broken, most of the time the printer also tells us jam position so we know which switch it is seeing a jam condition at. Check the switch operation by looking for them, and ensuring the arm is moving freely.
The other possibility is the machine with no data present shows no error but a error occurs when a print job is sent to it. If this is the case it is caused usally by incorrect paper size settings in printer paper size menu or the printer drivers paper size settings on installed driver in printers under control panel of computer, It can also be caused if the paper is feeding multi sheets from cassete due to dirty rubber rollers in printer itself or not picking paper from tray at all as the feed roller is slipping on paper in tray due to losing its grippyness.
I clean feed rollers with water, just slightly damp rag and rub the rubber surface of the feed roller, sometimes they are so worn they need replacing, I will post a pic for you and also here is the service manual
of a machine pretty much the same as yours.This is another uses post
on how he fixed his, please note this will be the same as yours only if jam only occurs after data is sent to your machine.