Consider a "door operator conversion" to a modern system if parts are unavailable. step-by-step troubleshooting guide for a particular error code?
The drive belt should be tight enough to prevent slipping but have enough "give" (usually 10-15mm of deflection) to avoid putting excessive strain on the motor bearings. schindler qks 14 door operator manual
Turn off power and move the doors by hand. If they feel heavy or "crunchy," the issue is likely mechanical (bearings or rollers) rather than electrical. Maintenance Safety Consider a "door operator conversion" to a modern