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Brother TN-845B Instruction Manual page 118

Twin needle needle feed lock stitcher with thread trimmer
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14. TROUBLESHOOTING GUIDE
14. FEHLERSUCHE
14. RECHERCHES DE PANNES
14. GUIA PARA LA LOCALIZACION DE FALLAS
Problem
3. Skipped stitches occur
while sewing
4. Skipped stitches at sewing
start
Thread unravelling at
sewing start
5. Uneven seam
¡
Is the needle tip bent? Is the needle tip blunt?
If the needle tip is bent or broken, replace the needle.
¡
Is the needle properly installed?
If it is incorrect, install the needle correctly.
¡
Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
¡
Is the presser foot pressure too weak?
Adjust the presser foot pressure.
¡
Is the sewing speed too fast?
Check whether the correct motor pulley (with the correct outer di-
ameter) that matches the maximum sewing speed and frequency of
your particular model and sewing specifications is being used.
If it is not correct, replace the motor pulley.
Depending on the type of material being used, skipped stitches may
occur even when sewing at the maximum sewing speed within the
rated range. In such cases, reduce the sewing speed slightly.
¡
Is the needle up stop position too high?
Adjust the needle position sensor.
¡
Are the lower thread retainer springs pressing against the lower
threads after thread trimming?
If the lower thread retainer springs are not pressing against the lower
threads, adjust the positions of the movable knives.
¡
Is the height of the feed dog correct?
Adjust so that the feed dog is 1 mm above the needle plate at its
highest position.
¡
Are the thread take-up spring tensions too strong?
Reduce the tension of the thread take-up springs.
¡
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 trailing lengths of the upper threads too short after thread
trimming?
Adjust the pretension.
¡
Are the threads not being trimmed cleanly?
Sharpen the fixed knives, or replace the fixed and movable knives if
necessary.
¡
Is the needle too wide?
Try using a needle with a count that is one lower than the current
needle.
¡
Is the presser foot for thick material (with slots) being used to sew
thin and medium material?
Use a presser foot with no slots.
Use a feed dog for thin and medium material.
¡
Is the sewing speed too fast at the sewing start?
Use the slow start feature.
¡
Is the presser foot pressure too weak?
Adjust the presser foot pressure.
¡
Is the feed dog too low?
Adjust the feed dog height.
¡
Is the bobbin scratched?
If the bobbin is damaged, smooth it with an oiled grindstone or re-
place it.
¡
Is the V-belt tension too low?
Adjust so that there is 10–20 mm of deflection in the V-belt when it
is pushed with a finger.
– 103 –
Where to check
Page
36
41 · 42 · 44
52
Motor
instruc-
tion
manual
83
79
(Step 5–7)
63
65
66
52
78
4 · 6 · 7 · 36
Motor
instruc-
tion
manual
52
63
18
TN-840B, 870B (English)
TL-840B
(English)

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