Lower-Thread Sensor - Bernina B 590 Service And Maintenance Manual

3.4 Lower-thread sensor

Issue:
Machine stops on its own while stitching. Lower-thread breakage message appears.
But the thread is not broken.
Possible sources:
• Brake spring is not properly inserted in bobbin carrier. A filled bobbin
should pop out of the bobbin carrier by a bobbin's side wall width.
Solution:
Insert new brake spring, making sure
That the bobbin carrier isn't damaged
or deformed (picture 1).
•
The reflectors on the bobbin border are worn, and the lower-thread
sensor doesn't recognize movements anymore.
Solution:
Replace with new bobbin (picture 2).
• Faulty lower-thread sensor signal.
Solution:
The signal can be tested in Service Program Test 3c
(lower-thread sensor).
(Picture 3). Replace lower-thread sensor if necessary.
Note:
With the 5 Series (VIO), it isn't possible to wind
the lower thread wrongly or insert the
bobbin into the bobbin case
the wrong way It works the same as with the 7 Series.
BERNINA International AG
a) A/B signal receiver
b) A/B signal sender
c) C signal sender
d) C signal receiver
e) Hook area lighting LED
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