Brother S-710A User manual

SL-710A
DB2-DD7100A
DB2-DD7100
Please read this manual before making any adjustments.
SINGLE NEEDLE DIRECT DRIVE STRAIGHT LOCK STITCHER
WITH THREAD TRIMMER
SERVICE MANUAL

SL-710A
i
This service manual is intended for SL-710A, DB2-DD7100A, DB2-DD7100 ; be sure to read the SL-710A, DB2-
DD7100A, DB2-DD7100 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
1. Safety indications and their meanings
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
DANGER The instructions which follow this term indicate situations where failure to follow the
instructions will almost certainly result in death or severe injury.
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.
Symbols
........................................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”.)

SL-710A ii
2. Notes on safety
DANGER
Wait at least 10 minutes after turnin
g
off the
p
ower switch and disconnectin
g
the
p
ower cord from the wall outlet
before o
p
enin
g
the face
p
late of the control box. Touchin
g
areas where hi
g
h volta
g
es are
p
resent can result in
severe injury.
CAUTION
Environmental requirements
Use the sewin
g
machine in an area which is free
from sources of stron
g
electrical noise such as
high-frequency welders.
Sources of stron
g
electrical noise ma
y
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
p
ower su
pp
l
y
ca
p
acit
y
should be
g
reater than
the re
q
uirements for the sewin
g
machine’s
electrical consumption.
Insufficient
p
ower su
pp
l
y
ca
p
acit
y
ma
y
cause
problems with correct operation.
The ambient tem
p
erature should be within the
range of 5 to 35 during use.
Tem
p
eratures which are lower or hi
g
her than this
may cause problems with correct operation.
The relative humidit
y
should be within the ran
g
e of
45 % to 85 % durin
g
use, and no dew formation
should occur in any devices.
Excessivel
y
dr
y
or humid environments and dew
formation ma
y
cause
p
roblems with correct
operation.
Avoid exposure to direct sunlight during use.
Ex
p
osure to direct sunli
g
ht ma
y
cause
p
roblems
with correct operation.
In the event of an electrical storm, turn off the
p
ower and disconnect the
p
ower cord from the
wall outlet.
Li
g
htnin
g
ma
y
cause
p
roblems with correct
operation.
Installation
Machine installation should onl
y
be carried out b
y
a qualified technician.
Contact your Brother dealer or a qualified electrician
for anyelectricalwork that mayneed to be done.
The sewin
g
machine wei
g
hs more than 36 k
g
.
The installation should be carried out b
y
two or
more people.
Do not connect the
p
ower cord until installation is
complete, otherwise the machine may operate if
the treadle is de
p
ressed b
y
mistake, which could
result in injury.
Be sure to connect the
g
round. If the
g
round
connection is not secure, you run a high risk of
receiving a serious electric shock, and problems
with correct operation may also occur.
When securin
g
the cords, do not bend the cords
excessivel
y
or fasten them too hard with sta
p
les,
otherwise there is the dan
g
er that fire or electric
shocks could occur.
If usin
g
a work table which has casters, the
casters should be secured in such a wa
y
so that
they cannot move.
Use both hands to hold the machine head when
tiltin
g
it back or returnin
g
it to its ori
g
inal
p
osition. If
onl
y
one hand is used, the wei
g
ht of the machine
head ma
y
cause
y
our hand to sli
p
, and
y
our hand
may get caught.
Be sure to wear
p
rotective
g
o
gg
les and
g
loves
when handlin
g
the lubricatin
g
oil, so that no oil
g
ets into
y
our e
y
es or onto
y
our skin, otherwise
inflammation can result.
Furthermore, do not drink the oil under an
y
circumstances, as the
y
can cause vomitin
g
and
diarrhea.
Keep the oil out of the reach of children.
Use a lam
p
which is rated at 6 V AC and 20 W or
less. If a lam
p
with a hi
g
her ratin
g
than this is
used, it could cause the lam
p
wires and the
transformer to overheat and burn out, which could
result in fire.

SL-710A
iii
CAUTION
Sewing
This sewing machine should only be used by
operators who have received the necessary
training in safe use beforehand.
The sewin
g
machine should not be used for an
y
applications other than sewing.
Be sure to wear
p
rotective
g
o
gg
les when usin
g
the
machine.
If goggles are not worn, there is the danger that if
a needle breaks,
p
arts of the broken needle ma
y
enter your eyes and injury may result.
Turn off the power switch at the following times,
otherwise the machine may operate if the treadle is
depressed by mistake, which could result in injury.
When threading the needle
When replacing the bobbin and needle
When not usin
g
the machine and when leavin
g
the machine unattended
If using a work table which has casters, the casters should
besecuredin sucha waysothattheycannotmove.
Attach all safet
y
devices before usin
g
the sewin
g
machine. If the machine is used without these
devices attached, injury may result.
Do not touch an
y
of the movin
g
p
arts or
p
ress an
y
ob
j
ects a
g
ainst the machine while sewin
g
, as this
ma
y
result in
p
ersonal in
j
ur
y
or dama
g
e to the
machine.
Use both hands to hold the machine head when
tiltin
g
it back or returnin
g
it to its ori
g
inal
p
osition. If
onl
y
one hand is used, the wei
g
ht of the machine
head ma
y
cause
y
our hand to sli
p
, and
y
our hand
may get caught.
If an error occurs in machine o
p
eration, or if abnormal
noises or smells are noticed, immediatel
y
turn off the
p
ower switch. Then contact
y
our nearest Brother
dealer or a qualified technician.
If the machine develo
p
s a
p
roblem, contact
y
our
nearest Brother dealer or a qualified technician.
Cleaning
Turn off the
p
ower switch before carr
y
in
g
out
cleaning, otherwise the machine may operate if
the treadle is de
p
ressed b
y
mistake, which could
result in injury.
Use both hands to hold the machine head when tilting it
back or returning it to its original position. If only one hand
is used, the weight of the machine head may cause your
hand to slip,and yourhand may getcaught.
Be sure to wear protective goggles and gloves
when handling the lubricating oil, so that no oil
gets into your eyes or onto your skin, otherwise
inflammation can result.
Furthermore, do not drink the oil under any
circumstances, as they can cause vomiting and
diarrhea.
Keep the oil out of the reach of children.
Maintenance and inspection
Disassembly, assembly, 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
treadle is depressed by mistake, which could
result in injury.
When carrying out inspection, adjustment and
maintenance
When replacing consumable parts such as the
rotary hook and knife
Turn off the power switch before inserting or
removing the plug, otherwise damage to the
control box could result.
Use both hands to hold the machine head when tilting it
back or returning it to its original position. If only one hand
is used, the weight of the machine head may cause your
hand to slip,and yourhand may getcaught.
If the power switch needs to be left on when
carrying out some adjustment, be extremely
careful to observe all safety precautions.
Be careful not to touch your fingers or the lubrication
amount check sheet against moving parts such as
the rotary hook or the feed mechanism when
checking the amount of oil supplied to the rotary
hook, otherwise injury may result.
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.

SL-710A iv
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.
4. About the ground symbol
There is a ground symbol which is shown on
the control box in the position shown in the
illustration.
If other equipment needs to be grounded,
connect the ground wire to the screw which
is next to this ground symbol.
If the ground connection is not secure, you
run a high risk of receiving a serious shock,
and problems with correct operation may
also occur.
Finger guard
0766M
2
1
Thread take-up cover
Safety devices
Finger guard
Thread take-up cover, etc.
2
1
Ground symbol
Screw
0767M

SL-710A
INDEX
1. SPECIFICATIONS.................................... 1
2. OPTIONAL PARTS.................................. 3
3. NOTES ON HANDLING .......................... 4
4. MECHANICAL DESCRIPTIONS ............. 5
4-1. Upper shaft and needle bar mechanism .......5
4-2. Lower shaft and rotary hook mechanism ......5
4-3. Feed mechanism...........................................6
4-4. Quick reverse mechanism.............................7
4-5. Lubrication mechanism
(Thread take-up lever and rotary hook)........8
4-6. Thread trimmer mechanism ........................10
4-6-1. Thread trimmer operation..........................10
4-6-2. Upper and lower thread trimming..............12
4-7. Tension release mechanism ........................13
4-8. Thread wiper mechanism.............................14
4-9. Presser foot lifter mechanism
(-9[][], Option) (built into machine head)......14
4-10. Lower thread detector mechanism.............15
5. DISASSEMBLY...............................................16
5-1. Bed cover and safety switch........................16
5-2. Connectors..................................................17
5-3. Solenoid-type presser lifter
(-9[][], Option) ..............................................17
5-4. Lower thread detector
(-31[], -41[], -91[], Option)............................17
5-5. Covers and operation panel ........................18
5-6. Tension release wire, ground wire and
thread trimmer solenoid...............................19
5-7. Wick holder and oil tube
(Thread take-up lever).................................20
5-8. Oil tank, Bed under cover and sub tank......20
5-9. Quick reverse solenoid................................21
5-10. Needle, presser hoot and
reverse actuator assy..................................22
5-11. Thread tension mechanism........................22
5-12. Needle plate and Feed dog .......................22
5-13. Bobbin case, rotary hook and
thread trimming mechanism........................23
5-14. Feed bar mechanism..................................23
5-15. Feed rocker shaft .......................................23
5-16. Presser foot mechanism.............................24
5-17.Knee lifter lever mechanism........................24
5-18. Needle bar and thread take-up mechanism25
5-19. Pulley and motor ........................................25
5-20. Timing belt..................................................26
5-21. Spring and feed regulator...........................26
5-22. Lower shaft, lower shaft gear and
feed regulator set.........................................27
5-23. Plunger, rotary hook shaft, gear
and thread trimmer cam ..............................27
5-24. Stitch length dial.........................................28
5-25. Reverse stitching lever and feed regulator.28
6. ASSEMBLY.......................................................29
6-1. Stitch length dial, reverse stitching lever
and feed regulator mechanism....................29
6-2. Rotary hook shaft, thread trimmer
cam and gear...............................................31
6-3. Plunger........................................................31
6-4. Lower shaft, lower shaft gear
and feed regulator set..................................32
6-5. Timing belt, motor and pulley ......................34
6-6. Knee lifter lever mechanism........................36
6-7. Needle bar and thread take-up mechanism 36
6-8. Presser foot mechanism..............................39
6-9. Feed rocker shaft ........................................40
6-10.Spring..........................................................40
6-11.Feed bar mechanism...................................41
6-12.Sub tank, wick holder and wick...................42
6-13.Thread tension mechanism.........................43
6-14.Oil (Feed rocker shaft).................................44
6-15.Thread trimming mechanism.......................44
6-15-1. Installing the thread trimmer cam lever 44
6-15-2. Adjusting the needle and
feed mechanism timing................................45
6-15-3. Installing the movable knife and
fixed knife.....................................................46
6-15-4. Adjusting the thread trimming timing....47
6-16.Rotary hook and bobbin case
holder position bracket ................................48
6-17.Ruler plate and needle plate .......................49
6-18.Reverse actuator assembly
and presser hoot..........................................49
6-18-1. Adjusting the presser foot height.............50
6-18-2. Adjusting the thread guide height............50
6-18-3. Adjusting the tension spring
vertical position............................................50
6-18-4. Adjusting the thread tension bracket
forward/back position...................................50
6-19.Tension release wire ...................................51
6-20.Quick reverse solenoid................................52
6-21.Bed under cover (Gear box)........................53
6-22.Oil tank ........................................................54
6-23.Tension release wire ...................................55
6-24.Ground wire.................................................55
6-25.Operation panel...........................................55
6-26.Face plate and thread take-up cover...........56
6-27.Safety switch ...............................................57
6-28.Arm cover, rear cover and
bobbin winder tension assembly.................57
6-29.Other devices ..............................................57
6-30.Connectors..................................................58
6-31.Lubrication...................................................59
6-32.Bed cover and knee lifter lever....................60
6-33.Test operation..............................................61
6-34.Adjusting the safety switch position.............62

SL-710A
7. ADJUSTMENTS..............................................63
7-1. Adjusting the thread tension spring.............63
7-2. Adjusting arm thread guide R......................64
7-3. Adjusting the presser foot height.................64
7-4. Adjusting of the feed dog height..................65
7-5. Adjusting the feed dog angle.......................66
7-6. Adjusting the needle bar height...................67
7-7. Adjusting the needle and
feed mechanism timing ...............................67
7-8. Adjusting the needle and rotary
hook timing..................................................68
7-9. Quick reverse mechanism...........................69
7-10.Matching stitch lengths for normal
feed and reverse feed..................................69
7-11.Synchronizer Adjustment ............................70
7-12.Adjusting the tension release wire...............71
7-13.Adjusting the treadle....................................72
7-14.
Adjusting the rotary hook lubrication amount
.......73
8. CONTROL SYSTEM ....................................75
9. REMOVING AND INSTALLING
THE CONTROL BOX...................................76
10. CONTROL BOX AND
MOTOR RATING PLATE...........................77
11. CONTROL CIRCUIT BOARD...................79
12. FUNCTION SETTING METHODS..........81
12-1.DIP switch functions....................................81
12-2.Parameter setting flowchart.........................82
12-3.Parameters..................................................83
12-4.Memory switch setting flowchart .................86
12-5.Memory switches.........................................87
13. TREADLE UNIT ASSEMBLY...................90
13-1.Types...........................................................90
13-2.Standard setting values...............................91
13-3.Setting method for standard
depression strokes ......................................92
14. STANDING OPERATION PEDAL...........96
14-1.Installing the foot plug..................................96
14-2.Connectors..................................................97
15. Puller
(commercially available)..........................98
15-1.Timing..........................................................98
15-2.Connector....................................................98
15-3.Binding the cord...........................................98
16. AUTO BOBBIN CHANGER......................99
16-1.Timing..........................................................99
16-2.Connector....................................................99
16-3.Binding the cord...........................................99
17. SPEED SETTING METHODS ............... 100
17-1.Types of speed settings............................ 100
17-2.Setting method.......................................... 100
17-3.Checking the speed settings..................... 101
18. CLEARING THE MEMORY DATA....... 102
19. CHECKING THE MOTOR AND
POWER SUPPLY...................................... 103
20. CHECKING THE SOLENOIDS............. 104
21. WIRING DIAGRAMS................................ 105
21-1.Control circuit board assembly ................. 105
21-2.Power supply circuit board assembly
(DD7100A, 710A) ..................................... 111
21-3.Power supply circuit board assembly
(DD7100) .................................................. 120
21-4.Transformer.............................................. 129
21-5.Operation panel B-40................................ 130
21-6.Operation panel B-100.............................. 133
22. TROUBLESHOOTING............................. 136
22-1.Sewing...................................................... 136
22-2.Error code displays................................... 143

1. SPECIFICATIONS
SL-710A
1
1. SPECIFICATIONS
Machine head
30 31 40 41 90 91
Thread trimmer Solenoid
Thread wiper Solenoid
Quick reverse Solenoid
Automatic presser lifter Solenoid
Bobbin thread detector
135
Use For light-weight and
difficult-to-sew For medium-weight materials For heavy-weight materials
Sewing speed 220 - 4,000 rpm 220 - 5,000 rpm * 220 - 3,500 rpm
Start backtacking and continuous backtacking
speed 220 - 1,800 rpm
End backtacking speed 1,800 rpm
Maximum stitch length 4.2 mm 5 mm
Needle bar stroke 29 mm 31 mm 35 mm
Thread take-up stroke 57.4 mm 61 mm
Feed dog 4 row 3 row 3 row (Long stitch)
Feed dog height 0.8 mm 1.2 mm
Presser bar lifter 6 mm
Knee lifter 13 mm
Presser
foot
height Automatic presser lifter 10 mm
Presser foot pressure 10 - 40N 40 - 79 N 57 - 98 N
Bed size 476 X 178 mm
Arm pocket size 266.5 X 134.5 mm
Needle (DB X 1) NS # 9 # 11 # 22
Rotary hook For light-weight
materials For medium-weight materials For heavy-weight materials
Motor AC servo motor (three-phase/single-phase, 4-pole, 400 W)
Control circuit Microprocessor
Weight 36 kg (41 kg for sub-class-900)
*… When using the rotary hook RP(Lubrication-free rotary hook),set the sewing speed to 4,000 rpm or less.
Models
DD7100- A
DD7100-
SL-710A-

1. SPECIFICATIONS
SL-710A 2
Operation panel
Operation panel Part code
B-40 J80627-001
B-100 J80629-001

2.OPTIONAL PARTS
SL-710A
3
2. OPTIONAL PARTS
Part name Part code
DD7100A, 710A S80008-001
Presser foot lifting solenoid setA With knee switch DD7100 183959-001
DD7100A, 710A S80009-001
Presser foot lifting solenoid set B Without knee switch DD7100 183960-001
DD7100A, 710A S80007-001
Lower thread detector set DD7100 183955-001
Thread wiper set 183956-001
Tension gauge set 183922-101
Sensor ll J80755-001
Part name Part code
Set for new synthetic fabric * For -[][]3 models 183910-101
If changing -[][]1 models to new synthetic fabric specifications, or if using the machine with standard specifications but
with the rotary hook replaced by the rotary hook RP (lubrication-free rotary hook), please use the following parts.
S44338-901 (Rotary hook box assembly)*
S35786-001 (Cap screw)
* …When using the rotary hook RP (lubrication-free rotary hook), set the sewing speed to 4,000 rpm or less.
Table parts
Part name Part code
Standing operation 2 pedal #6
(Two pedals +kick pedal) J80081-040
Standing operation 3 pedal #40
(Three pedals) J80380-040
Standing operation 3 pedal two-speed
(Three pedals) J80630-001
Spacer set 183504-009
Caster set 183501-001
Foot plug set, NDD (for control box) J02953-001
0772M
0773M
0527M
0528M
1144M

3. NOTES ON HANDLING
SL-710A 4
3. NOTES ON HANDLING
About the machine set-up location
• Do not set up this sewing machine near other equipment such
as televisions, radios or cordless telephones, otherwise such
equipment may be affected by electronic interference from the
sewing machine.
• The sewing machine should be plugged directly into an AC
wall outlet. Operation problems may result if extension cords
are used.
Carrying the machine
• The machine should be carried by the arm by two people as
shown in the illustration.
* Do not hold the machine by the machine pulley.
Tilting back the machine head
• While pulling the bottom rear of the bed toward you with your
left hand, push the top right of the arm body with your rigth
hand to tilt back the machine head.
* Be careful not to get your left hand caught between the
bottom of the bed and the table.
Returning the machine head to the upright position
1. Clear away any tools, etc. which may be near the table holes.
2. While holding the face plate with your left hand, gently return
the machine head to the upright position with your right hand.
0777M
0776M
0775M
0774M

4. MECHANICAL DESCRIPTIONS
SL-710A
5
4. MECHANICAL DESCRIPTIONS
The mechanisms operate in the order of the numbers given in the illustrations.
4-1. Upper shaft and needle bar mechanism
4-2. Lower shaft and rotary hook mechanism
1627M
8 Lower shaft gear
7 Lower shaft
3 Join
t
4 Timing pulley U
2 Roto
r
1 Pulle
y
6 Timin
g
pulle
y
D
5 Timing bel
t
9 Gea
r
10 Rotary hook shaft ass
y
11 Rotary hook
1626M
5 Needle take-up leve
r
4 Thread take-up crank 3 Upper shaf
t
2 Rotor 1 Pulle
y
7 Slide bloc
k
8Needle ba
r
(1)
(2)
6Needle bar
clamp
The needle bar is guided by the needle bar bush U (1) and needle bar bush D (2).

4. MECHANICAL DESCRIPTIONS
SL-710A 6
4-3. Feed mechanism
Vertical movement of feed bar
Horizontal movement of feed bar
1629M
1628M
1 Pulle
y
1 Pulle
y
3 Level feed
eccentric wheel
4 Level feed
connecting rod
5 Feed regulator ass
y
6 Feed
7 Feed rocker bracket arm
8 Feed ba
r
2 Lower shaf
t
2 Lower shaft
4 Feed ba
r
3 F-lifting eccentric
wheel assy

4. MECHANICAL DESCRIPTIONS
SL-710A
7
4-4. Quick reverse mechanism
1. When the actuator is pressed lightly, the movement is transmitted to the various parts as shown in the illustration, so
that the angle of the feed regulator assembly is reversed.
2. When the angle of the feed regulator assembly is reversed, the feed rocker arm link and feed rocker arm change from
normal feed to reverse feed.
* Operation occurs in the same way as described above even when the reverse stitching lever (1) is lowered.
1632M1631M
<Normal feed> <Reverse feed>
4 Shaf
t
1A ctuato
r
2 Quick reverse solenoid
3Solenoid leve
r
5 Handle shaft arm
6 Connecting rod
7 Stud arm
9 F-regulator connecting rod S
13 Feed rocker shaf
t
12 Feed rocker arm
10 Feed regulator ass
y
8 Join
t
11 Feed rocker arm lin
k
13 Feed rocker shaf
t
12 Feed rocker arm
11 Feed rocker arm lin
k
10 Feed regulator ass
y
(1)
1630M

4. MECHANICAL DESCRIPTIONS
SL-710A 8
4-5. Lubrication mechanism (Thread take-up lever and rotary hook)
The lubrication mechanism for this sewing machine is a dry head method, with the oil supplied from a tank.
The oil level can be checked through the oil gauge window, without needing to tilt back the machine head or operate the
sewing machine.
DD7100A, 710A
When adding the lubricating oil for the first time after unpacking the sewing machine, pour 130 ml of lubricating oil in
through oil filler hole (1). The oil gauge in the oil gauge window (2) will rise as far as the upper reference line. (Refer to
page 59 for details on the lubrication method.)
1. The lubricating oil that is poured into the oil filler hole (1) is stored in the oil tank (3).
2. The lubricating oil in the oil tank (3) is drawn up by the plunger pump (4).
3. The lubricating oil in the sub tank (5) is transferred to parts such as the thread take-up lever and needle bar by wicks.
* The rotary hook lubrication amount can be adjusted using the adjusting screw (6). (Refer to page 73.)
(2)
(3)
(4)
(5)
(1)
(6)
(6)
(5)
1636M
1635M
1634M
1633M
To upper shaft, thread take-up
lever, needle bar, etc.
Used oil To rotary hook and rotary
hook shaft
Upper reference line
Oil gauge
Lower reference line
(2) Oil gauge window
Plunger pump
Oil gauge
Increase
Decrease
(4)

4. MECHANICAL DESCRIPTIONS
SL-710A
9
DD7100
When adding the lubricating oil for the first time after unpacking the sewing machine, pour 120 ml of lubricating oil in
through oil filler hole (1). The oil gauge in the oil gauge window (2) will rise as far as the upper reference line. (Refer to
page 59 for details on the lubrication method.)
1. The lubricating oil that is poured into the oil filler hole (1) is stored in the oil tank (3).
2. The lubricating oil in the oil tank (3) is drawn up by the plunger pump (4).
3. The lubricating oil that is drawn up by the plunger pump (4) is transferred to parts such as the thread take-up lever and
needle bar by oil tubes and wicks.
* The rotary hook lubrication amount can be adjusted using the adjusting screw (6). (Refer to page 73.)
(2)
(1)
(6)
(4)
(6)
(4)
(3)
1638M1635M1634M
1637M
Used oil
Upper reference line
Oil gauge
Lower reference line
(2) Oil gauge window
Plunger pump
Oil gauge
IncreaseDecrease
To rotary hook and rotar
y
hook shaft
To upper shaft, thread take-up
lever, needle bar, etc.

4. MECHANICAL DESCRIPTIONS
SL-710A 10
4-6. Thread trimmer mechanism
4-6-1. Thread trimmer operation
The figure below shows the thread trimmer without the high-speed rotary hook.
1) When the thread trimmer signal is received
2) Thread trimmer holder action
1639M
1 Solenoid plunge
r
2 Solenoid leve
r
3 Thread trimmer cam lever shaft
4 Roller
(Moves over thread trimmer cam (1))
(1)
1640M
1 Thread trimmer cam
2 Roller
3 Roller block
4 Forked shaf
t
5 Thread trimmer leve
r
6 Thread trimmer
connecting rod
7 Thread trimmer holde
r
8 Movable knife

4. MECHANICAL DESCRIPTIONS
SL-710A
11
3) Thread trimming complete stop
4) Thread trimmer safety device
When the movable knife does not return to its original position, the mechanism operates as shown in the illustration
below to move the movable knife to a position where it will not touch the needle.
1642M
1641M
(1) Thread trimmer lever
1 Spring
2 Thread trimmer leve
r
(3) Thread trimmer holde
r
3 Solenoid leve
r
<2> Forked shaf
t
4 Solenoid
plunger
(2) Thread trimmer
connecting rod
<1> Thread trimmer leve
r
(4) Movable knife
<3> Roller bloc
k
<4> Rolle
r
1 Thread trimmer cam
2 Return pin
3 Roller bloc
k
4 Forked shaft
5 Thread trimmer lever
6 Thread trimmer connecting rod
7 Thread trimmer holde
r
8 Movable knife

4. MECHANICAL DESCRIPTIONS
SL-710A 12
4-6-2. Upper and lower thread trimming
1. When the needle rises 1.8mm (2.2mm with heavy-
wei
g
ht materials
)
above the down
p
osition the rotar
y
hook point catches the loop formed by the needle.
2.The thread trimmer si
g
nal is then rela
y
ed, and the
thread trimmer cam drives the movable knife. The
rotar
y
hook catches the u
pp
er thread and
p
asses it
through the inner rotary hook.
3. The tip of the movable knife passes through the middle of the triangular loop formed underneath the needle plate
by the rotary hook to separate the upper and lower threads.At this time, the thread take-up lever moves up slightly
from its lowest position. (The angular movement of the upper shaft is approximately 330°.)
* If the timing of this operation is advanced, it will affect the separation of the upper and lower threads by the
movable knife, and it may result in thread trimming errors.
4. The u
pp
er and lower threads cau
g
ht b
y
the movable knife in 3 above are
g
raduall
y
s
p
read b
y
the knife and lower
thread fin
g
er and cut b
y
the fixed knife ti
p
. The thread take-u
p
lever has now a
pp
roached the to
p
of its stroke.
When the knife is s
p
readin
g
the thread, the tension release relieves the u
pp
er thread tension to
p
revent excessive
tension and to enable the u
pp
er thread to be smoothl
y
extended. The len
g
th of thread s
p
read b
y
the movable knife
determines the len
g
th of thread remainin
g
from the needle ti
p
and bobbin when thread trimmin
g
is com
p
lete, and
effects stitch formation at the beginning of the next sewing procedure.
Movable knife
Movable knife
Lower thread
finger
Lower thread
Fixed knife
Movable knife
U
pp
er thread
Lower thread
Movable knife
Lower thread
finger
Fixed knife
1643M
1646M
1648M
1647M
1645M
1644M
(
As seen with fixed knife removed
)
Upper thread

4. MECHANICAL DESCRIPTIONS
SL-710A
13
4-7. Tension release mechanism
9 Discs
8 Disc presse
r
5 Tension release plate
4 Tension
release wire
7 Pin
2 Bol
t
3 Solenoid lever
6 Tension release stud
1 Thread trimmer
solenoid
3 Solenoid leve
r
1 Thread trimme
r
solenoid
6 Tension release stud
5 Tension
release plate
4 Tension release wire
Disc presse
r
Tension release
stud Pin
4 Tension
release wire
2 Bol
t
When raising the presser foot using a knee lifter or knee switch
Discs 2 Presser bar
lifter lever
1 Knee lifter
connecting rod
4 Tension
release stud
3 Tension
release plate
1649M
1652M
1653M
1651M
1650M Seen from underneath
When a thread trimming
signal is input