T-8421C, 8422C, 8452C, 8722C, 8752C
14. TROUBLESHOOTING
78
Problem Possible cause Page
9 Upper and lower threads
are breaking.
y Is the needle bent or is the needle tip broken?
Replace the needle if it is bent or broken.
y Is the needle properly installed?
If it is incorrect, install the needle correctly.
y Is the machine properly threaded?
If it is incorrect, thread the thread correctly.
y Is the oil tank filled with lubricating oil?
If the level of lubricating oil is below the bottom reference line,
add more oil.
y Is the upper or lower thread tension too weak or too strong?
Adjust the upper thread or lower thread tension.
y Is the rotary hook blocked with dust or thread scraps?
Clean the rotary hook.
y Is the upper thread may be loose because the thread take-up spring
operating range is too small?
Adjust the position of the stopper.
y Is the rotary hook, feed dog or other part damaged?
If they are damaged, smooth them with an oiled grindstone or
replace the damaged parts.
y Is the thread path damaged?
If the thread path is damaged, smooth it with sandpaper or
replace the damaged part.
y Is the thread take-up amount correct?
Adjust the thread take-up amount.
18
20-24
9
51
55
65*
*
*
54
10 Incorrect thread trimming y Is the movable knife damaged or bent?
Replace the movable knife
*
11 Broken needles y Is the material being pushed or pulled with excessive force during
sewing?
y Is the needle bent, is the needle tip broken, or is the needle hole
blocked?
Replace the needle.
y Does the needle drop into the center of the needle hole in the feed
dog?
Check the needle drop position. If the needle does not drop into
the center of the needle hole in the feed dog, reinstall the feed
dog.
If the needle bar has rotated, rotate the needle bar to the
correct position.
y 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.
y Furthermore, we recommend we recommend that through
steps be taken to account for such needles to comply with
product liability regulations.
18
*
*
12 Machine does not operate
when power is turned on
and treadle is pressed.
y Is the power supply connector
disconnected from the control
box?
Insert the connector
securely.
14
• 15
0471M
Caution
0469M
2197B
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