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The easiest way to adjust the cable tension is to rotate the idler brackets.
If One Cable is Loose, or You are Adjusting the X Axis Square:
You will need a 4mm hex wrench and a 10mm wrench.
At the rear of the print volume there is a bracket that holds 2 idler pulleys on each Y rail. One of these
pulleys is mounted in a slot. By loosening the screw you can slide the pulley to adjust the tension.