Brother CB3-B917 User manual

CB3-B916A
CB3-B917A
SERVICE MANUAL
Please read this manual before making any adjustments.
CHAINSTITCH BUTTON SEWER
CHAINSTITCH BUTTON SEWER WITH THREAD TRIMMER

CB3-B916A/B917A i
This service manual is intended for B916A/B917A; be sure to read the B916A/B917A instruction manual before this manual.
Carefully read the "SAFETY INSTRUCTIONS" below and the whole of this manual to understand this product before you start
maintenance.
As a result of research and improvements regarding this product, some details of this manual may not be the same as those for
the product you purchased.
If you have any questions regarding this product, please contact a Brother dealer.
SAFETY INSTRUCTIONS
This service manual and the indications and symbols that are used on the machine itself are provided in order to ensure safe
operation of this machine and to prevent accidents and injury to yourself or other people.
The meanings of these indications and symbols are given below.
Indications
Symbols
CAUTION The instructions which follow this term indicate situations where failure to follow the instructions
could cause injury when using the machine or physical damage to equipment and surroundings.
DANGER The instructions which follow this term indicate situations where failure to follow the instructions
will almost certainly result in death or severe injury.
................This symbol ( ) indicates something that you should be careful of. The picture
inside the triangle indicates
the nature of the caution that must be taken.
(For example, the symbol at left means “beware of injury”.)
................This symbol ( ) indicates something that you must not do.
................ This symbol ( ) indicates something that you must do. The picture inside the
circle indicates the nature of the thing that must be done.
(For example, the symbol at left means “you must make the ground
connection”.)
1. Safety indications and their meanings

ii CB3-B916A/B917A
2. Notes on safety WARNING
CAUTION
Do not put your hand into any openings near the belt, as your hands could get caught in
the belt, and serious injury could result.
Environmental requirements
Use the sewing machine in an area which is free
from sources of strong electrical noise such as
high-frequency welders.
Sources of strong electrical noise may cause
problems with correct operation.
Any fluctuations in the power supply voltage
should be within ±10% of the rated voltage for
the machine.
Voltage fluctuations which are greater than this
may cause problems with correct operation.
The power supply capacity should be greater
than the requirements for the sewing machine's
electrical consumption.
Insufficient power supply capacity may cause
problems with correct operation.
The ambient temperature should be within the
range of 5°C to 35°C during use.
Temperatures which are lower or higher than
this may cause problems with correct operation.
The relative humidity should be within the range
of 45% to 85% during use, and no dew
formation should occur in any devices.
Excessively dry or humid environments and dew
formation may cause problems with correct
operation.
Avoid exposure to direct sunlight during use.
Exposure to direct sunlight may cause problems
with correct operation.
In the event of an electrical storm, turn off the
power and disconnect the power cord from the
wall outlet.
Lightning may cause problems with correct
operation.
Installation
Machine installation should only be carried out
by a qualified technician.
Contact your Brother dealer or a qualified
electrician for any electrical work that may need
to be done.
The sewing machine weighs more than 25 kg.
The installation should be carried out by two or
more people.
Do not connect the power cord until installation
is complete, otherwise the machine may operate
if the pedal is depressed by mistake, which
could result in injury.
Be sure to connect the ground. If the ground
connection is not secure, you run a high risk of
receiving a serious electric shock, and problems
with correct operation may also occur.
All cords should be secured at least 25 mm
away from any moving parts. Furthermore, do
not excessively bend the cords or secure them
too firmly with staples, otherwise there is the
danger that fire or electric shocks could occur.
Install the belt covers to the machine head and
motor.
If using a work table which has casters, the
casters should be secured in such a way so that
they cannot move.
Be sure to wear protective goggles and gloves
when handling the lubricating oil and grease, so
that they do not get into your eyes or onto your
skin, otherwise inflammation can result.
Furthermore, do not drink the oil or eat the
grease under any circumstances, as they can
cause vomiting and diarrhoea.
Keep the oil out of the reach of children.

CB3-B916A/B917A iii
CAUTION
Sewing
This sewing machine should only be used by
operators who have received the necessary
training in safe use beforehand.
The sewing machine should not be used for any
applications other than sewing.
Be sure to wear protective goggles when using
the machine.
If goggles are not worn, there is the danger that
if a needle breaks, parts of the broken needle
may enter your eyes and injury may result.
Turn off the power switch at the following times,
otherwise the machine may operate if the pedal
is depressed by mistake, which could result in
injury.
* The motor will keep turning even after the
power is switched off as a result of the motor’s
inertia. Wait until the motor stops fully before
starting work.
• When threading the needle
• When replacing the needle
• When not using the machine and when leaving
the machine unattended
If using a work table which has casters, the
casters should be secured in such a way so that
they cannot move.
When turning the machine pulley by hand in
order to check the needle down position in the
hole of the button, turn the pulley until the
needle is at the final position after one cycle.
If the needle is at a point midway through the
cycle when the power is turned on, the machine
will immediately start operating, which could
result in injury.
Attach all safety devices before using the
sewing machine. If the machine is used without
these devices attached, injury may result.
Do not touch any of the moving parts or press
any objects against the machine while sewing,
as this may result in personal injury or damage
to the machine.
If an error occurs in machine operation, or if
abnormal noises or smells are noticed,
immediately turn off the power switch. Then
contact your nearest Brother dealer or a
qualified technician.
If the machine develops a problem, contact your
nearest Brother dealer or a qualified technician.
Cleaning
Turn off the power switch before starting any
cleaning work, otherwise the machine may
operate if the pedal is depressed by mistake,
which could result in injury.
* The motor will keep turning even after the
power is switched off as a result of the motor’s
inertia. Wait until the motor stops fully before
starting work.
Be sure to wear protective goggles and gloves
when handling the lubricating oil and grease, so
that they do not get into your eyes or onto your
skin, otherwise inflammation can result.
Furthermore, do not drink the oil or eat the
grease under any circumstances, as they can
cause vomiting and diarrhoea.
Keep the oil out of the reach of children.
Maintenance and inspection
Maintenance and inspection of the sewing
machine should only be carried out by a
qualified technician.
Ask your Brother dealer or a qualified electrician
to carry out any maintenance and inspection of
the electrical system.
Turn off the power switch and disconnect the
power cord from the wall outlet at the following
times, otherwise the machine may operate if the
pedal is depressed by mistake, which could
result in injury.
* The motor will keep turning even after the
power is switched off as a result of the motor’s
inertia. Wait until the motor stops fully before
starting work.
• When carrying out inspection, adjustment and
maintenance
• When replacing consumable parts such as the
loopers and knife.
When turning the machine pulley by hand, turn
the pulley until the needle is at the final position
after one cycle.
If the needle is at a point midway through the
cycle when the power is turned on, the machine
will immediately start operating, which could
result in injury.
If the power switch needs to be left on when
carrying out some adjustment, be extremely
careful to observe all safety precautions.
Use only the proper replacement parts as
specified by Brother.
If any safety devices have been removed, be
absolutely sure to re-install them to their original
positions and check that they operate correctly
before using the machine.
Any problems in machine operation which result
from unauthorized modifications to the machine
will not be covered by the warranty.

iv CB3-B916A/B917A
3. Warning labels
The following warning labels appear on the sewing machine.
Please follow the instructions on the labels at all times when using the machine. If the labels have been removed or are
difficult to read, please contact your nearest Brother dealer.
123
4
Safety devices:
Eye guard, Finger guard,
Needle bar cover, Pulley covers,
etc.
Attach the high temperature
label to the motor in a place
where it will be easily visible.
5
Be sure to connect the ground. If the ground connection is
not secure, you run a high risk of receiving a
serious electric shock, and problems with correct operation
may also occur.
Direction of operation
<Rear>
1
3
Pulley covers
(Option)
<Motor>
Pulle
y
cover
Center of
p
ulle
y
Machine head
fixin
g
hole
Pulle
y
cover
Motor
(37)
(37)
60
120
101.5
101.5
(Seen from above work table)
<Diagram of installation position for pulley covers (Option)>
Needle bar cover
Eye guard
2
Finger guard
5
4

CONTENTS
1. MECHANICAL DESCRIPTIONS ---------------1
1-1. Start mechanism 1
1-2. Number of stitches changing 2
1-3. Brakemechanism 3
1-4. Needle bar mechanism 4
1-5. Looper mechanism 4
1-6. Feed mechanism 5
1-7. Thread trimmer mechanism 7
1-8. Button clamp mechanism 8
1-9. Tension release mechanism 9
2. DISASSEMBLY---------------------------------10
2-1. Cover 10
2-2. Clutch 10
2-3. Button clamp 11
2-4. Looper 12
2-5. Number of stitches changing 13
2-6. Needle bar 14
3. ASSEMBLY AND ADJUSTMENT----15
3-1. Needle bar 15
3-2. Number of stitches 17
3-3. Loopre 19
3-4. Button clamp 24
3-5. Clutch 25
3-6. Cover 26
4. REPLACEMENT OF PARTS------------28
4-1. Horizontal feed cam, vertical feed cam,
worm gear, worm,
number of stitches adjustment cam 28
4-2. Cushion rubber 33
5. ADJUSTMENTS---------------------------------35
5-1. Needle bar height 35
5-2. Loop spreader 35
5-3. Point where needle and looper meet 35
5-4. Clearance between needle bar and looper 35
5-5. Needle guard 35
5-6. Fixed knife 35
5-7. Movable knife 36
5-8. Stitch number 36
5-9. Number of stitches adjustment cam 36
5-10.Pawl of thread trimming lever 36
5-11.Button clamp driving lever 36
5-12.Worm and worm gear backlash 37
5-13.Pulley clearance in thrust direction 37
5-14.Slider 37
5-15.Auxiliary tension timing 38
5-16.Thread tension timing 38
5-17.Loop spreader timing 38
5-18.Forward and reverse feed 38
5-19.Button clamp installation 39
5-20.Elevation amount of button clamp 39
5-21.Feed timing 39
5-22.Clutch lever 39
5-23.Brake 39
5-24.Button clamp opener (B917A) 40
5-25.Thread take-up lever 40
5-26.Main tension 40
5-27.Rotor 41
5-28.Button clamp pressure 41
6. Troubleshooting-----------------------------------42
4-3. Driving lever pawl 34

1.MECHANICAL DESCRIPTIONS
CB3-B916A/B917A
1
Clutch lever
Clutch assembly
Ball presser plate
Ball bearing 5/16
Pulley
Stop cam
Drive shaft
2.Press
3.Press
Lower shaft
4.Clutch mounts here
1.Depress pedal
101s
1. MECHANICAL DESCRIPTIONS
1-1. Start mechanism
Clutch connects here
Press in with the ball
presser plate
102s

1. MECHANICAL DESCRIPTIONS
CB3-B916A/B917A 2
1-2. Number of stitches changing
Number of stitches
control lever
Number of stitches
adjustment lever Number of stitches
adjustment cam
Number of stitches 6, 8
104s
Number of stitches 12, 16
105s
Stitch 32 lever
Roller
Number of stitches
adjustment gear
Number of stitches 24, 32
106s
107s
Roller

1.MECHANICAL DESCRIPTIONS
CB3-B916A/B917A
3
1-3. Brake mechanism
1.Drop
Clutchshaft
Clutch
Ball presser plate
2.Drop
3.Clutch released
Number of stitches control lever
108s
Clutch released
109s
Ball presser plate

1. MECHANICAL DESCRIPTIONS
CB3-B916A/B917A 4
1-4. Needle bar mechanism
1-5. Looper mechanism
Drive shaft
Drive shaft
Helical gear
Lower shaft helical gear
Lower shaft
Triangular cam
Looper (Rotary)
112s
Loop spreader
Loop spreader base
1. Rotation
2. Eccentric
3. Vertical motion
4. Rocking motion
6. Vertical motion
5. Rocking motion
Needle bar clamp
connector
Needle bar clamp
Needle bar
Needle
Needle bar drive lever
Crank rod
Stop cam
Pulley
111s
113s
Loop spreader guide
Triangular cam
114s
Loop spreader groove
cam
115s

1. MECHANICAL DESCRIPTIONS
CB3-B916A/B917A
5
1-6. Feed mechanism
1-6-1. Vertical feed mechanism
117s
Drive shaft
Drive shaft helical gear
Lower shaft helical gear
Lower shaft
Worm
Worm gear
Cam shaft
Vertical feed cam
Feed roller
Feed roller shaft
Vertical feed lever
Slide block
Vertical feed connecting
rod
Vertical feed link A
Feed bracket
Feed plate
1. Rotation
2. Right – left
3. Rocking
4. Forward – back
5. Forward -back
118s
Vertical feed
adjustment lever
Vertical feed scale
116s

1. MECHANICAL DESCRIPTIONS
CB3-B916A/B917A 6
1-6-1. Horizontal feed mechanism
Button hole spacing 2 mm
Button hole spacing 6 mm
121s
122s
119s
Drive shaft
Drive shaft helical gear
Lower shaft helical gear
Lower shaft
Worm
Worm gear Cam shaft
Vertical feed
cam
Feed roller
Feed roller shaft
Horizontal feed
lever
Feed link
Feed bracket
Feed plate
1. Rotation
4. Right - left
3. Rocking
120s
2

1. MECHANICAL DESCRIPTIONS
CB3-B916A/B917A
7
1-7. Thread trimmer mechanism
124s
125s
126s
Number of stitches 6, 8
Number of stitches 12, 16
Number of stitches 24, 32
Thread trimming lever
Number of stitches adjustment lever
Number of stitches adjustment cam
Number of stitches
ad
j
ustment
g
ear
Stitch 32 lever
Roller
123s
1. Rotation
Cam shaft
Number of stitches adjustment cam
Pawl
Thread trimming
lever
Connecting rod
Connecting lever
Thread cutter connecting rod
Movable knife
7
2
3
4
65
Fixed knife

1. MECHANICAL DESCRIPTIONS
CB3-B916A/B917A 8
1-8. Button clamp mechanism
1-8-1. Button clamp descent (sewing start)
1-8-2. Button clamp lift (machine stop)
127s
2
1. Depress pedal
Clutch lever
Clutch
Clutchshaft
Button clamp driving lever
Button clamp driving
connecting rod
Button clamp driving lever
Button clamp lifter
connecting rod
Button clamp lifter
arm
Button clamp arm
assembly
Driving link
Button clamp
regulating
plate
3
4
5
6. Pawl is disengaged and
arm is raised by tension
spring.
7
8
9
10
Operating lever pawl
Spring
Button clamp
presser spring
4. Pawl is caught and
lever is pulled down.
128s
2
Number of stitches
control lever
Clutchshaft
Button clamp driving
lever
Driving link
Button clamp driving
connecting rod
Button clamp lifter
connecting rod
Button clamp lifter
arm
Button clamp regulating
plate
Button clamp arm
assembl
y
Button clamp driving
lever
3
5
6
7
8
9
Driving cam
Button clamp operating fork
1

1.MECHANICAL DESCRIPTIONS
CB3-B916A/B917A
9
1-8-3. Button clamp opener [B917A]
1-9. Tension release mechanism
Size adjustment
plate
Button clamp opener
lever
Button clamp opener
claw Button clamp
opener lever Button clamp plate cam
Button clamp
129s
131s
130s
Claw adjustment
p
late
Disconnects
Thread
tension Auxiliary tension Main tension
Machine stopped O O X
Sewing O Opens at each
stitch X
O -> X -> OFinal stitch B917A
B916A O -> X -> X Differs according to needle bar
position X
O-Tension discs open
X-Tension discs close
Auxiliary tension (Opens
at each stitch)
Slider
132s
Thread tension (Tightens
on final stitch onl
y)
Main tension (Thread
tension is alwa
y
s ke
p
t.
)
Rocking
Needle bar
drive lever
133s
Slider Final stitch
During machine
o
p
eration Machine stop
(B916A : non)
Returns to
original
position

2. DISASSEMBLY
CB3-B916A/B917A 10
2. DISASSEMBLY
2-1. Cover
2-2. Clutch
Turn off the power switch before starting any
cleaning work, otherwise the machine may
operate if the pedal is depressed by mistake,
which could result in injury.
* The motor will keep turning even after the
power is switched off as a result of the motor’s
inertia. Wait until the motor stops fully before
starting work.
Disassembly of the sewing machine should only
be carried out bya qualified technician.
If any safety devices have been removed, be
absolutely sure to re-install them to their original
positions and check that they operate correctly
before using the machine.
CAUTION
Be sure to wear protective goggles and gloves
when handling the lubricating oil and grease, so
that they do not get into your eyes or onto your
skin, otherwise inflammation can result.
Furthermore, do not drink the oil or eat the grease
under any circumstances, as they can cause
vomiting and diarrhoea.
Keep the oil out of the reach of children.
Use only the proper replacement parts as
specified by Brother.
Any problems in machine operation which result
from unauthorized modifications to the machine
will not be covered by the warranty.
201s
1. Button tray
2. Eye guard
3.
Needle
4.Sub–tension
thread guide 5.
Face
plate
4. Face plate thread guide
4. Needle bar cover
4. Face plate thread guide 6. Top cover
7. Bolt
8. Arm cover
8. Looper cover
1. Ball presser plate
2. Ball bearing (5/16)
3. V-belt
4. Pulley
5. Ball bearing (7/32)
6. Spring
7. Set screw
8. Clutch tension spring
10. Clutch
202s
9. Brake

2. DISASSEMBLY
CB3-B916A/B917A
11
2-3. Button clamp lifter
203s
Button clamp
1. Spring guide
1. Spring
2. Button clamp arm
3. Holder shaft
4. Stud screw 6.35
204s
5. Button clamp
lifter arm shaft
6. Button clamp lifter arm
Button clamp opener claw
Claw adjustment plate

2. DISASSEMBLY
CB3-B916A/B917A 12
2-4. Looper
205s
1. Feed plate
2. Needle plate
206s
3. Loop spreader
4. Disconnecting rod
207s
5. Movable knife
6. Fixed knife
7. Needle guard
8. Loop spreader guide
9. Loop spreader base
208s
10. Looper
11. Looper setting shaft
12. Roller
14. Loop spreader groove cam
13. Loop spreader link
[B917A]
[B917A]

2. DISASSEMBLY
CB3-B916A/B917A
13
2-5. Number of stitches changing
1. Stitch 32 lever
2. Set collar
9. Snap ring
3. Number of stitches
adjustment gear
10. Number of stitches
adjustment M gear
Number of stitches control lever
8. Number of stitches adjustment cam
7. Thread trimming lever
Thrust washer
209s
210s
4. Snap ring
5. Connecting rod
6. Spring
[B917A]

2. DISASSEMBLY
CB3-B916A/B917A 14
2-6. Needle bar
211s
1. Needle thread
take - up
2. Needle bar
3. Needle bar clamp
4. Needle bar clamp
connector
5. Spring 6. Adjustment stud
7. Tension release rod
212s
11. Needle bar drive lever
9. Set collar 8. Crank rod upper part
Mark
Mark
10. Drive lever shaft