JUKI SC-20 Quick start guide

aJUKI
SC-20 SC-120
SC-220 SC-320
ENGINEER'S MANUAL
SC-20
SC-320
No. 1-35-3
1990.7
From the library of: Superior Sewing Machine & Supply LLC

PREFACE
The engineer's manual is written for the technical personnelwho are responsible for the service and maintenance of the
sewing machines. This manual presents detailed explanation of the adjusting procedures, etc. which are not covered by
the INSTRUCTION MANUAL intended for the maintenance personneland operators at a garment factory.
It is advisable to use this engineer's manual is combination with the pertinent INSTRUCTION
MANUAL and PARTS
LIST when servicingthe sewing machines of these models.
OPERATION PRECAUTIONS
Z Oo not put your (irsgers into the thread take-up cover
while (he machine is operating.
4. During operation, be careful not to allow your or any
Other person's head or hands to come close to the
handwheel, V bell, bobbin winder or motor. Also, do
not place anything close to them. Doing so may be
dangerous. i 1_
6. To achieve security, be sure that the power supply
earth wire has been connected before ope'ating the
sewing machine.
1. Keep hands away from (he needle when the
power switch is turned ON or while the machine it
operating.
3. Be sure to turn the power switch OFF before tilling
the machine head or removing the V belt
S. If your machine is provided with a belt cover, finger
guard or any other protectors, do not operate your
machine with any of them removed.
7. No motor sound is heard when the sewing machine is
not operating. So. do not forget to turn the power
OFF at the end of work.
From the library of: Superior Sewing Machine & Supply LLC

i •'* *•'
CONTENTS
1. GENERAL • •••••; •• ^
1-1. Features • • • . 1
2. OPERATION 3
2-1. Name ofpart 3
2-2. Test run ^
2-3. SC-20 Powerindicatorbox ^
2-4. SC-120 Control panel ^
2-5. SC-220 Control panel ®
2-6. SC-320 Control panel 12
3. ADJUSTMENT 21
3-1. Belt tension 21
3-2. Prevention motor vibration (for Ncompany'smotor) 21
3-3. Checkingand correcting the rotational direction of sewingmachine 21
3-4. Pedal 22
3-5. Maximum sewing speed 25
3-6. Auto-lifter 27
3-7. Howto reduce the handlightfrom flickering (for single phaseonly) 28
4. FUNCTIONS 29
4-1. Power supply voltage 29
4-2. Functions selection switches 30
4-3. Increase of control panel functions 44
44. Safety circuit 46
4-5. Connectors for standing work 48
4-6. Production control systemand needle-upstop switch functions 50
5. MAINTENANCE AND INSPECTION 51
5-1. Howto replacethe sensorpotentiometer set 51
5-2. Memory battery charging monitor LED (SC-320 only) 53
5-3. Motor malfunction detector LED 53
54. Solenoid monitor LED 54
5-5. How to replace each circuit board 55
5-6. Troubleshooting 64
5-7. Circuit board installment diagrams 75
5-8. Connector connection diagrams 80
5-9. Type of rating plates for SCseries of the PSC unit 81
5-10. Block diagrams 82
From the library of: Superior Sewing Machine & Supply LLC

1. GENERAL
1-1. Features
1) Use ofan AC servomotor provides the following mqor advantages:
(1) No noise or vibration while the machine is at rest.
(2) The power consumption is 40% to 60% compared with the conventional power consumption.
(3) The motor weight has been almost halved, permitting easier layout change.
(4) The absence ofa clutch (no brake in case ofN company's motor) makes theunit virtually maintenance-fiee.
(H company's brake is good for more than10 years under normal operation.)
Unlike the DC servomotor, there is no bmsh.
2) Pedaloperation features
(1) Youcansetthe maximum sewing speed in400 s.p.m.
stepswith fingertipcontrol according to the type of
operation and your level of proficiency.
(In the conventional unit, the motor pulleyhad to
be changedto alter the maximum sewing speed.)
Further, you canget the samespeedat any time.
(2) The conventional speed limit knobis also provided.
So, by combining the knob with the function
mentioned in(1) above, high-speed playstrokecan
be provided. This eliminatesthe need for large
pedalingforce to maintain high speed,significantly
reducing operator foot fatigue.
(3) The speed acceleration starting pointcanbe adjusted
about 1mm (0.039") by pedal stroke to suit with
each operator.
(4) The minimumspeedfor depressing the front part of
the pedal can be changed(from 200 s.p.m. to 400
s.p.m.).
High-speed'
play stroke
Pedal depression amount
(3) 1mm (0.039 'l
adjustable by ^
pedal stroke >/
/ (4) 400 spm
_t 200 spm
Pedal depression amount
3) Reverse feedstitchingfeatures
(1) As in the conventional model, you can select either the mode in which priority is given to pedaling for the
starting reverse feed stitching orthe mode in which the machine performs nonstop reverse feed stitching at
a preset speed.
(2) The reverse feed stitching speed has been increased from 1,700 s.p.m. to 1,900 s.p.m. (about 12% increase).
Furthermore, the speed canbe adjusted from 1,000 s.p.m. to 3,500 s.p.m., using the variable resistor.
(3) The speed control circuitry has been improved to prevent overrun or 1-stitch error when the reverse feed
stitching speed is changed.
4) Thesoftstart speedhasbeen increased.
The soft start speed for assuring properly interlaced threads ofa starting stitch has been increased from 200 s.p.m.
to 800 s.p.m.
The soft start speed is now adjustable within a range of 200 s.p.m. to 2,000 s.p.m., so you do not have to drop
the speed more than necessary.
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5) Enhanced series with easy upgrading • '•^ ^ ^
Thecontroller comes inthe SC-20, SC-120, SC-220, SC-320 and SC-522 series, andyoucan easily upgrade them
simply by replacing their control panels (excluding the SC-522). ?; > ..
6) A manualcount-downcapabilityhasbeen added.
As an additional capability, the manual count-down capability has been added to the one-touch type reverse feed
switch to provide the control based ofa preset number of stitches.
Description Applications
Count back
When the one-touch type reverse feed switch
is pressed,the preset number of stitches is
counted down.
Sewing pleats
Count back + Thread trim
When the one-touch type reverse feed switch
ispressed,the preset number of stitches is
counted down, and threads are trimmed.
Replaces the reverse feed
stitching at a seam end.
(This feature is especially useful
in a sewing machine for standing
work because the need for
operating the thread trimmer
switch is eliminated.)
7) Even ifa material overlap at sewing startorendis thick, the needle will notbe caught inthe thick overlap.
(After thread trimming, youcanturnthe handwheel inthe reverse direction to bring the needle barup to its
highestposition.)
8) Aconnectorfor standing workhasbeen provided asa standarditem.
9) A terminal for connection to a sewing control system hasbeen provided.
10) The automatic presser foot lifting capability can be added simply by adding the AK auto-lifter and a transistor
circuit board.
11) The control panel is very easy to operate and the slant panel surface makes it easier to see indication on the panel.
12) To ensure easier operation of the control panel, each key has been assigned to only one function.
13) You can setthe lifting duration ofthe Auto-lifter after thread trimming for60 sec. or ten minutes.
(For a sewing machine for standing work, it is advisable to set the lifting duration for ten minutes.)
14) The output transistor has been designed to be a unit circuit board to make ita common part. If any trouble
should occur, the minimum function is assured.
(Example : If the thread trimmer transistor fails, the wiper transistor will work to permit thread trimming and
reversefeed stitching.)
15) The trouble checking feature for the output system (output monitor LED) has been added to the conventional
input system. This enables you to quickly and easily identify defective parts.
16) Reliability
The machine uses only the components which have passed our reliability test conducted on each discrete component.
17) We are planning to provide the following options inthe future:
Sewing controlcounter(oflowcost)
18) The machine controller now can be applied to the control of the ED-1 (cloth edge sensor) (Optional).
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2. OPERATION
2-1. Name of part
O Power switch
oControl box
0Synchronizer
O
L-shaped threadstand
0 PSCbox
0 Max.speed control knob
0Motor
m
0 Pedal
0One-touch type reverse feedswitch
0 Wiper
0 Stand levelling screw(or caster)
0 400 s.p.m.-step speed control knob
0 Connector for standing operation
0 Connector for production control system
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O Power switch
Power switch for the motor, PSC and control box.
0Control box
Used to make settings for automatic reverse feed stitching, the number ofstitches forpattern sewing orother
sewing conditions.
®Synchronizer
Incorporated in the machine pulley, the synchronizer detects the needle position (up or down) and the se^ymg
speed, then sends a resultant input signal to the main circuit board inthe PSC box. . .
O
L-shaped thread stand
0 PSC box
Comprises a circuitry to control the sewing machine and motor, an output circuitry to operate the elements (thread
trimming solenoid, reverse feed solenoid, etc.), a pedal sensor to detect pedal position, and a power circuitry to
actuate the elements.
0 Max. speed controlknob
Allows analog adjustment of the maximum sewing speed without changing themotor pulley.
0 Motor
Operates the machine at high speed medium speed low speed in response toa signal received from the PSC box.
(AnH company's motoris provided witha brake.)
0 Pedal
The front and back parts ofthe pedal are depressed to control the sewing speed and to actuate the thread trimmer,
presser footlifter (only fora version with AK-31, AK-34), etc.
© One-touch type reverse feed switch
Usedby hand to perform reverse feed stitching.
# Wiper
Wipes the needle thread off the material after thread trimming in response toa wiper signal received from the
PSC box.
0 Stand levelling screw (or caster)
Used to perform adjustment sothatthe stand rests flatly onthe floor to minimize vibration during operation.
0 400 s.p.m.-step speedcontrol knob
This switch has 16 steps from 1to 16in order to digitally setthe maximum speed in400 s.p.m. steps.
0Connector for standing operation
Used fora sewing machine designed for standing operation.
0 Connector for production control system
Usedto connect the machine to a production control system.
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2-2. Test Run ^
1) Operationwhen the power switchis turned ON
When the power switch is turned ON, if the needle isnot initsupperstop position, the machine rotates untilits €?
needle reaches the upper stop position, and then stops with its needle in that position.
If the needle is already in its upper stop position when the power switch is turned ON, the sewingmachine stays
stationary.
'-Uf
2)Pedal operation
(1) Thepedalisoperatesin the foUowing four steps, (exceptfora Version with AK-31, AK-34)
©—
High speed
Low speed
Stop
Thread trimming
High speed
Low speed
Stop (neutral)
Thread trimming
The sewing machine runs at low speed when you depress the front part of the pedal.
The sewing speed changes fromlowto highwhenthe front part of the pedalisfurther depressed.
(However,if the automatic reverse feed stitching switch has been set, the machine willnot mn at high speed
until it completes reverse feedstitching.)
When the pedalis returnedto the neutralposition(stop position),the machine will stop with needle down.
When the backpart of the pedalis depressed, the thread trimmerisactuated and the needlegoesup and
stops in its upper position.
(When the wiperswitchhasbeenset to ON,the wiperisactuated.)
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7^
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(2) In caseof a versionwith AK-31,AK-34
The pedalisoperated in the
following fivesteps:
High speed
Low speed
Stop
Presser foot lifting
Thread trimming
@
High speed
Low speed
Stop (neutral)
Presser foot lifting
Thread trimming
o The sewing machine startsat low speed whenthe front part of the pedalislightly depressed,
o The sewing speed changes from lowto highwhenthe front part of the pedalis further depressed.
(However, if the automatic reverse feed stitching switch has been set,the sewing speed will not change to
highuntil reverse feed stitching iscompleted.)
o When the pedalis returned to the neutral(stop) position,the machine stopswith its needledown,
o When the backpart of the pedal islightly depressed, the presser foot will goup.
o When the backpart of the pedalisfurther depressed, the presser foot comesdown,thread trimmeris
actuated, and the machine stops with its needle up.
(If the wiperswitchhas been set to ON, the wiperis actuated.)
o Between the lowandhigh sewing speedpositions, the machine runsat a speedcorresponding to the pedal
depressionamount. (The speed is infinitely variable.)
o The proper thread trimmingaction willnot be disturbed evenif the pedal is returned to the neutral
position immediatelyafter the machinestarts thread trimming.
At this time, the thread trimmerproperlyoperates even if the front part of the pedalisdepressed, however,
the safetycircuitryisput in operationso that the machine will not mn after thread trimming iscompleted.
Therefore, the pedal must be returned to the neutral position once.
2-3. SC-20 Power Indicator Box
1) Power indicator LED
o Lights up when the power switch is turned ON.
o This light stays ON for a while after the power is turned OFF. It is dangerousto carry out maintenance or
adjustment with the PSC box cover open. Be sure that the LED is OFF before starting maintenance such as
part replacement.
SC- 2 0
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2-4. SC 120 Control panel
1) Control panel
Automatic reverse stitching (for end) indicator
lamp (LED)
•Lights when the ending reverse stitching
switch is ON.
Power indicator lamp (LED)
• Lights up whenthe powerswitchisturned ON.
• Stays ON for a while immediately after the
power switch is turned OFF.
It is dangerous to perform any maintenance
work with the PSC box cover open.
Be sure that the lamp is OFF before per
forming maintenance work such as parts
replacement.
Switch for raising the needle.
• If this switch is turned ON when the machine
stops with its needle down, the needle goes up
and stops in its upper position.
• By depressing the back part of the pedal, the
thread trimmer may be actuated.
(Note that this switch will be invalid when the
needle has been moved down by hand.)
2) Howto use the automatic reverse stitchingpatterns
Automatic reverse
switching (for start)
switchO
Stitching pattern
Automatic reverse
stitching (for end)
switch 0
OFF ON
OFF OFF
OFF
ON
NN
ON
ON
m m
Automatic reverse stitching (for start) indicator
lamp (LED)
•Lights when the starting reverse stitching
switch is ON.
Switches for setting the number of stitches
• These are pushbutton switches for setting the
numbers of stitches for steps A and B.
The setting range is from 0 to 9.
[+]... .Increases the number of stitches
B . . . .Decreases the number of stitches
Automatic reverse stitching (for start) switch
• Used to turn ON or OFF automatic reverse
stitching at sewing start.
• Each time this switch is pressed, it alternately
turns ON or OFF. (This switch is rendered
invalid when the number of stitches for step B
has been set to "0".)
Automatic reverse stitching (for end) switch
• Used to turn ON or OFF automatic reverse
stitching at sewing end.
• Each time this switch is pressed, it alternately
turns ON or OFF. (This switch is rendered
invalid when the number of stitches for step B
has been set to "0".)
m
El m
By combining ON and OFF conditions of automatic reverse
stitching (for start) switch O and automatic reverse stitching
(for end) switch O , four different stitching patterns are
available.
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