First, the choice of time to see if the head is bright, with or without stripping paint and bumps phenomenon, needle plate, push plate, panel, the last round of plating is intact; platen is flat, paint and whether there is a crack or local discoloration; Rack is broken, paint off, crooked; axis under the shaft, needle bar gap is in line with standard requirements.
Second, remove the belt, board pressure foot, gently turn the upper wheel, whether it works freely, the needle is in the middle of needle plate hole.
Third, whether the machine sound soft rotation.
Fourth, test step, sewing time, the first two layers of thin cloth test seam, check the pin is flat, uniform. And then try the original seam, to see if the pin length can reach 3.6mm, there is no material to go seamless or abnormal sound and so on.
Fifth, more specific testing should be sewing machine maintenance workers in the presence.