Brother LH4-B800E, Service Manual

Page: 120 / 168

LH4-B800E
5 - 5
5. Troubleshooting guide
Cause Check Solution page
Lower thread
retainer Lower thread retaining
amount
Adjust the lower thread
retaining amount.
4-19
Lower thread
clamp
Lower thread clamp
timing
Adjust so that the lower
thread clamp plate
opens when the feed
mechanism moves 6 --
7 mm.
Adjust the lower thread
clamp opening timing.
4-20
Beginning of sewing (2) Lower thread lifted up
* The end of the lower thread protrudes above the seam at the sewing start
Beginning of sewing (3) Seam lifts up
* Seam lifts up and does not tighten at the sewing start
Beginning of sewing (4) Uneven sewing pitch
* Bird's nests form at the sewing start, and after 5 -- 6 mm the sewing pitch suddenly increases.
1 - 2 mm
Cause Check Solution page
Upper thread
scissors
Upper thread scissors
gradual opening timing
Adjust the gradual
opening timing of the
upper thread scissors.
Upper thread scissors gradually
start opening when the feed
mechanism moves about 1.5 -- 2.5
mm.
4-17
Upper thread
feeding
Refer to "5-3. Uneven seams 1)......Beginning of sewing (1)"
Cause Check Solution page
Lower thread
clamp
Lower thread clamp
timing
Adjust the opening
timing of the lower
thread clamp. Advance the timing at which the
lower thread clamp starts to open.
4-20