Brother VX641 - Uneven Seams of Reverse Patterns; Breaking of Upper Thread; Breaking of Lower Thread

TROUBLE AND CAUSE
CORRECTION
Refer to:
INSTRUCTION
BOOK or:
13. UNEVEN SEAMS OF REVERSE PATTERNS
Refer to: SERVICE MANUAL (Item No.)
following models
(1 ) Improper setting of reverse feed devices
vX710
9 - 1
VX720
10 - 1
VX511. VX541. VX561. VX581. VX516. VX546. VX566. VX586. VX611. VX641
VX661. VX681. VX616. VX646. VX666. VX686. VX720. VX740. VX760. VX780
9-2
VX541. VX561. VX581. VX546, VX566. VX586. VX641, VX661
VX681, VX646. VX666. VX686. VX740. VX760. VX780
10 - 2
14. BREAKING OF UPPER THREAD
(1 ) Incorrect relation of needle & thread
(2) Bent or blunt needle
(3) Inferior needle eye
(4) Incorrect threading
(5) Inferior needle slot of needle plate
(6) Upper thread tension too tight
(7) Scratch on the shuttle hook
Relative chart
Change the needle
Change the needle
Upper threading
Change needle plate
Thread tension
Change the shuttle hook
15. BREAKING LOWER THREAD
(1 ) Not smooth running of bobbin
(2) Scratch on tension spring of bobbin case
(3) Scratch on the shuttle hook
(4) Lower thread tension too tight
Change the bobbin
Change the spring
Change the shuttle hook
Thread tension