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trouble shooting [ 1 ] [ 2 ]

Upper thread defective incomplete  

Probable causes

Actions

Thread take-up spring incomplete contact
Securely couple connectors
Tension base connector incomplete contact
Securely couple connectors
Upper thread breakage timing contact incomplete
Clean and adjust the upper thread breakage timing contact

  Deformed design

Probable causes

Actions

Frame drive belt is too tight
Loosen
Frame guide rails are clogged with foreign materials
Clean the rails
Frame drive circuit defective
Replace
Memory plate defective
Replace
Overall weight of the frame is excessive
Decrease R, P. M