Problem Cause ; Remedy ; Upper thread breaks. - Page 149

10. TROUBLESHOOTING

BAS-311G, BAS-326G   

142

Problem Cause 

Remedy 

Reference

Upper thread tension is too strong. 

Adjust the upper thread tension. 

P. 89 

Needle is incorrectly installed. 

Install the needle correctly. 

Instruction 

manual

Thread is too thick for the needle. 

Select a thread that matches the needle.

P. 89 

Thread take-up spring tension and 
height are incorrect. 

Adjust the tension and height of the 
thread take-up spring. 

P. 90 

Damage or burring of the rotary hook, 
needle hole plate or needle. 

Repair or replace the problem part. 

Thread breaking from heat (Synthetic 
thread) 

Use a cooling tank. 

Instruction 

manual

Upper thread breaks. 

Thread is threaded incorrectly. 

Thread the thread correctly. 

Instruction 

manual

Lower thread tension is too strong. 

Adjust the lower thread tension. 

P. 89 

Lower thread breaks. 

Damage to corners of needle hole plate 
or bobbin case. 

Repair or replace the problem part. 

Clearance between needle and rotary 
hook tip is too great. 

Adjust the needle clearance. 

P. 92 

Needle and rotary hook timing is 
incorrect. 

Adjust the needle bar lift amount. 

P. 91 

The driver is covering the needle more 
than necessary. 

Adjust the driver needle guard. 

P. 91 

Needle is bent. 

Replace the needle. 

Skipped stitches occur. 

Needle is incorrectly installed. 

Install the needle correctly. 

Instruction 

manual

Adjust the needle clearance. 

P. 92 

Clearance between needle and rotary 
hook tip is too great. 

Adjust the needle bar lift amount. 

P. 91 

Needle is bent. 

Replace the needle. 

Needle deflection 

Select a needle that is suitable for the 
sewing conditions. 
Reduce the sewing speed. 

P. 89 

Needle is broken. 

Needle is too thin. 

Select a needle that is suitable for the 
sewing conditions. 

P. 89 

Thread take-up spring tension and 
height are incorrect. 

Adjust the tension and height of the 
thread take-up spring. 

P. 90 

Needle and rotary hook timing is 
incorrect. 

Adjust the needle bar lift amount. 

P. 91 

Thread jamming. 

Shuttle race thread guide is not 
separating the threads. 

Adjust the position of the shuttle race 
thread guide. 

P. 92