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14. TROUBLESHOOTING GUIDE
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Be sure to check the following before calling an authorized service station.
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If the suggestions given below do not solve the problem, turn off the power and contact the place of purchase or
your nearest Brother dealer.
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Turn off the power switch and disconnect the power cord before carrying out troubleshooting, otherwise
the machine will operate if the treadle is pressed by mistake, which could result in injury.
Problem
1. Poor thread tightening
2. Needle thread and bobbin
thread break.
All manuals and user guides at all-guides.com
CAUTION
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Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
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Is the thread take-up spring operating range too small?
Adjust the operating range of the thread take-up spring.
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Is the needle thread tension and/or bobbin thread tension too low?
Adjust the upper and lower thread tensions.
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Is the bobbin scratched?
If the bobbin is damaged, smooth it with an oiled grindstone or re-
place it.
A sewing machine adjusted for medium thick material is used.
The type of material being sewn may result in poor thread tight-
ening.
Install a presser foot with a gap at the back (for thick materials).
Use a channeled feed dog (for thick materials).
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Is the needle tip bent? Is the needle tip blunt?
If the needle tip is bent or broken, replace the needle.
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Is the needle properly installed?
If it is incorrect, install the needle correctly.
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Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
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Is the rotary hook properly lubricated?
If the oil level is below the lower reference line in the oil sight glass,
add more oil.
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Is dust or thread in the rotary hook?
Clean the rotary hook.
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Is the upper thread tension too strong or too weak?
Adjust the upper thread tension.
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Is the rotary hook, feed dog or other part damaged?
If they are damaged, smooth them with an oiled grindstone or re-
place the damaged parts.
– 102 –
14. TROUBLESHOOTING GUIDE
14. FEHLERSUCHE
14. RECHERCHES DE PANNES
14. GUIA PARA LA LOCALIZACION DE FALLAS
Where to check
Page
41 · 42 · 44
66
51
36
41 · 42 · 44
60
60
51
TN-840B, 870B (English)
TL-840B
(English)
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