The Scheppach hms 260 planers and others are very like each other. Ask the distributor for a manual it is very good and gives loads of setup info on belt tightening setting up the cutters greasing the needle rollers 8-9 needle rollers etc. I stripped mine last summer I searched the web and found there are detailed manuals with useful annotations added.
To your question the motor provides belt driven power. the rubber rollers for the timber feed mechanism is chain and gear driven and the cutter head is belt driven with a tiny belt.
the motor belt tension is gravity Assisted in that you slacken the motor mount and the weight of the motor pivots and takes the slack out of the belt. so slacken off the motor mount from the side of the planer you can see the vertical slot with a nut in it in the picture below beneath the letter h in sheppac. Tilt the planer and rest it 45degrees or more against something substantial, it is very heavy. Access to the motor and belt is from the base lift and rotate the motor after slackening that bolt, remove the belt and try the motor without any load. If you wanted you could disengage the feed Rollers drive by turning the drive feed lever from Ein to Aus (on to off) as in the photo below but it is simple though a little awkward to remove the Motor belt
so unless there are some seized bearings a broken and jammed feed roller chain I'd suspect a faulty motor start capacitor or the like. Then if you have a faulty motor you're already most of the way through removing it! Check the roller feed, cutter head drive mechanism by removing that blue cover visible in the photo. Exceedingly unlikely to be the cutter head seizing but the rubber rollers run in plain bearings and are very difficult to lubricate. could be the chain tensioner mechanism that has broken or the chain but that is easily checked with a 10mm spanner and an Allan key to remove the feed mechanism lever.and the blue plastic cover