14. TROUBLESHOOTING GUIDE
14. RECHERCHES DE PANNES
14. GUIA PARA LA LOCALIZACION DE FALLAS
10. Trailing lengths of the
upper threads are too
short after thread trim-
11. Thread wiper is hitting the
Needle up stop position is
not consistently the same.
12. Broken needles
Is the thread coming out of the cotton stand easily?
If the thread is not coming out easily, check if the thread is caught
Is the tension of the pretension too strong?
Adjust the pretension.
Are the thread take-up spring tensions too strong?
Make the thread take-up spring tensions weaker.
Are the ranges of movement for the thread take-up springs too large?
Reduce the ranges of movement of the thread take-up springs.
Are the hooks of the movable knives damaged?
Polish the hooks to remove the damage, or replace the damaged
Are the tension discs moving during thread trimming?
If the tension discs are not moving, adjust the tension release mecha-
Is the timing correct during thread trimming?
Adjust the timing for thread trimming.
Is the thread wiper correctly positioned?
Adjust the thread wiper.
Is the needle up stop position too low?
Adjust the needle position sensor.
Is the V-belt tension too weak?
Adjust the tension so that the V-belt shows a deflection of 10–20 mm
when pushed with a finger.
Is the material being pushed or pulled with excessive force during
If the needle tip is bent or broken, replace the needle.
Does the needle pass the center of the needle hole in the feed dog?
Check the needle down position. If the needle does not drop into the
middle of the needle hole in the feed dog, re-install the feed dog.
[842B, 847B, 872B]
If the needle bar has been turned, turn it again to set it to the cor-
It is extremely dangerous to leave any pieces of broken needle
sticking in the material. If the needle breaks, search for all pieces
until the whole of the needle is found again.
Furthermore, we recommend that thorough steps be taken to ac-
count for such needles to comply with product liability regula-
– 105 –
Where to check
85 · 86
TN-840B, 870B (English)