Hi Tim,
Do these checks in this order;
1. Check error history from "Test 7: Record" of self-diagnostic function.
2. Set the number of endurance running cycles to 50 or more from "Life 2: PF Motor" of self diagnosis function, and check if X motor error" occurs.
3. Check "Encoder PF" from "Check 2: Test" – "Test 5: Encoder" of self diagnosis function.
4. PF Motor assembly may be defective
5. Main Board assembly may be defective
I trust you will understand this and I hope this can help!…. it means nothing to me 🙂