Samsung ProXpress m3870fw printer keeps jamming

I have Samsung ProXpress m3870fw. Half the times I try to print, there is a jam. Sometimes I just have to open the papers tray and remove the jammed paper, and sometimes the jam is on the rear.

I am using A4 80-gram paper.

I tried to remove all the removable parts of the printer and see if there is a paper that stayed there and causes to the jam, but there was nothing.

There is something to do?

(Sorry if my English grammar is not very good...)

Thank's!

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