Brother LH4-B800E Service Manual download pdf (Page 131)

LH4-B800E

5 - 16

5. Troubleshooting guide

Cause Check Solution page

Machine

stopping

position

Rotary hook touches

lower thread retainer at

the stop position

Adjust the needle up

stop position.

-

Presser foot

rise speed is

too fast

Memory switch No. 02.

(presser foot rise

speed)

Reduce the presser

foot rise speed.

Change using memory switch No.

02..

-

(Instruction)

Upper thread

scissors

Interference between

upper thread scissors

and cloth presser

Check the standard

adjustments,

particularly for joint

sewing.

Refer to "4-13-6. Adjusting the installation

height of the upper thread scissors"

(Remove the upper thread scissors to check.)

Upper thread scissors

operation

Carry out upper thread

scissors standard

adjustments.

4-12

Lower thread

trimmer

Interference between

fixed knife set, lower

thread clamp, lower

thread presser and

lower thread retainer.

Repair or replace the

parts.

-

Rubbish, dust or

thread scraps present

Remove all rubbish,

dust and thread scraps

from the lower thread

trimmer.

-

Loose screws Check for loose screws

in the upper thread

trimmer, lower thread

trimmer and presser

lifter mechanisms.

Securely tighten all

screws.

-

Presser foot

lifter height

Memory switch Nos.

04., 05. and 06.

Adjust so that the

memory switch setting

value matches the

presser foot rise height.

If the presser foot rise height is too

high, the lower thread trimming and

presser foot rising will become

harder and the pulse motor may go

out of step.

-

(Instruction)

threading Bobbin thread

threading

Insert the bobbin

correctly and pass the

lower thread through

the bobbin case

correctly.

If the bobbin is inserted back-to-

front, it will spin loosely and the

presser lifter may go out of step.

-

(Instruction)

Lower thread tension

(if the lower thread

tension is too strong,

step errors may occur)

Reduce the lower

thread tension.

Reduce the setting for

the presser foot lifting

speed (memory switch

No. 02.) to reduce the

lifting speed.

Buff this section to reduce the

thread retaining resistance.

-

Presser foot

lifter home

position

sensor

Presser foot lifter home

position sensor

position

Adjust the presser foot

lifter home position

sensor position.

4-5

Folding clamp is not raised (2) Pulse motor stepping sound can be heard

Retainer

Inner rotary

hook presser

Lower thread

trimmer link A

Lower thread

trimmer

connecting rod

Remove the shoulder

screw to check.

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