Janome JP720 User manual

SERVICING
MANUAL
JP720 & JP760

INDEX

What to do when................................................................................................................................................................ １-３
Changing External Parts
Face Cover.................................................................................................................................................................................４
Bed Cover ................................................................................................................................................................................５
Front Cover............................................................................................................................................................................６-７
RearF Cover..............................................................................................................................................................................８
Mechanical Adjustment
Presser Bar Height..................................................................................................................................................................９
Needle Drop Position..........................................................................................................................................................１０
Needle Bar Height................................................................................................................................................................１１
Needle to Hook Timing.......................................................................................................................................................１２
Clearance between Needle and Hook Point...............................................................................................................１３
Backlash ( Lower Shaft Gear ).........................................................................................................................................１４
Feed Dog Height...................................................................................................................................................................１５
Needle Swing Timming.......................................................................................................................................................１６
Top Tension............................................................................................................................................................................１７
Stretch Stitch Feed Balance.............................................................................................................................................１８
Thread Plate...........................................................................................................................................................................１９
Replacing the Electronic Components
Location of the Connectors .............................................................................................................................................２０
Diagnosis chart...............................................................................................................................................................２１-２３
Circuit Board-A......................................................................................................................................................................２４
Circuit Board-F.......................................................................................................................................................................２５
Driving Motor..........................................................................................................................................................................２６
Switching regulator Motor..................................................................................................................................................２７
Stepping motor ( Zigzag )...................................................................................................................................................28
Stepping motor ( Feed )......................................................................................................................................................29
Buttonhole lever guide.........................................................................................................................................................30
Oiling ...........................................................................................................................................................................................31

1
Condition Cause How to fix Reference
1. Skipping
Stitches 1. Needle is not inserted properly.
2. Needle is bent or worn.
3. Incorrectly threaded.
4. Needle or thread are
inappropriate for fabric being
sewn.
5. Sewing on stretch fabric.
6.Presser foot pressure is too weak.
7.In appropriate needle bar height.
8. Inappropriate needle to hook
timing.
9. Inappropriate needle to hook
clearance.
Insert the needle properly.
Change the needle.
Rethread.
Use the recommended sewing needle and
thread.
Use a HA x #11 blue tip needle.
Adjust the presser bar level to make the
pressure stronger.
See mechanical adjustment " Needle bar
height ".
See mechanical adjustment " Needle to
hook timing ".
See mechanical adjustment " Clearance
between needle and hook ".
P. 11
P. 12
P. 13
2. Fabric not
moving 1.Foot pressure foot is too weak.
2. Incorrect feed dog height.
3. Feed dog is in down position.
4.Thread on bottom side of fabric is
jammed up.
5. Feed dog teeth are worn.
Adjust the presser bar level to make the
pressure stronger.
See mechanical adjustment " Feed dog
height ".
Raise the feed dog.
Make sure to bring both needle and bob-
bin threads under the foot when starting
sewing.
Change the feed dog.
P. 15
What to do when

2
Condition Cause How to Fix Reference
3. Breaking
uper thread. 1. Initial sewing speed is too fast.
2.Thread path is incorrect.
3. Needle is bent or dull.
4.Top tension is too strong.
5. Needle size is inappropriate for
fabric.
6. Needle eye is worn.
7. Needle hole in needle plate is
worn or burred.
Start with medium speed.
Use the proper thread path.
Replace with a new needle.
Adjust top tension correctly.
Use appropriate needle for fabric and
thread in use.
Change the needle.
Repairthe hole orreplace the needle plate.
P. 17
4. Breaking
bobbin thread. 1. Bobbin holder is incorrectly threaded.
2.Too much thread is wound on the
bobbin,
3. Lint is stuck inside the bobbin
holder.
4.Thread quality is too low.
5.Thread is jamming around the
bobbin holder.
Set the bobbin thread correctly.
Adjust the position of bobbin winder
stopper.
Clean the bobbin holder.
Change to a high quality sewing thread.
Clear out the jamming thread.
5. Needle
breakes 1.Needle is hitting the needle plate.
2. Needle is bent or worn.
3. Needle is hitting the hook.
4.The fabric moves while the needle
is piercing it, or the needle zigzags
while in fabric.
5. Fabric is being pulled too strongly
while sewing.
See mechanical adjustment " Needle
drop position ".
Change the needle.
See mechanical adjustment " Clearance
between needle and hook ".
Seemechanical adjustment" Needleswing
timing ".
Guide the fabric gently while sewing.
P. 10
P. 13
P. 16

3
Condition Cause How to fix Reference
6. Noisy
operation 1.Backlash between hook gear and lower shaft gear is too great.
2. Lower shaft gear is loose.
3. Inappropriatte belt tension.
4. Not enough oil
See mechanical adjustment
“backlash (lower shaft gear)”.
Eliminate the looseness.
See part removal and replacement
“driving motor (dc motor)”.
Oil all moving parts.
P. 14
P. 26
P. 34
7. Deformation
pattern 1.Inappropriate feed balance.
2. Inappropriate needle swing
timing.
3.Top tension is too strong.
See mechanical adjustment
“stretch stitch feed balance”.
See mechanical adjustment
“Needle swing timing”.
See mechanical adjustment
“Top tension”.
P. 18
P. 16
P. 17

4
Changing External Parts
Face cover
To remove:
1. Loosen the screw and lift the face cover to disengage the rib on the inside. Remove the face cover .
To attach:
2. Attach the face cover ,engaging the hook and the rib with the rear cover and tighten screw .
q
q
w
w
e
e
r
r
t
t
t
q
w

5
Bed cover
Changing External Parts
To remove:
1. Shift the drop lever to the left .
2. Loosen 4 screws and remove the bed cover .
To attach:
Follow the above procedures in reverse.
q
w e
q
w
e
w
w

6
Changing External Parts
Front cover
1. Remove the face cover. (See page 4)
2. Loosen the set screw and then remove the set screw and .
3. Remove the cap and loosen set screw .
4. Disconnect all the connectors from the circuit board-A.
NOTE:
Do not disconnect the connectors by pulling on cord.
To disconnect, grasp the connector, not the cord.
(To be continued)
q
q
e
e
w
r
r
t
t
y
y
w

7
Changing External Parts
Front cover
4. Disengage the hooks and stitch balance adjustment knob .
5. Remove the front cover.
q
q
w
w
To attach:
Follow the above procedures in reverse.

8
Changing External Parts
Rear cover
To remove:
1. Remove the front cover. (See pages. 6, 7)
2. Loosen set screws , , , , ,and , then remove the rear cover .
NOTE:
Remove the presser lifter from the rear cover first while presser lifter lowered.
To attach:
Follow the above procedures in reverse.
q
q
w
w
e
e
r
r
t
t
y
y u
u

9
６.０mm
Mechanical Adjustment
The distance between the bottom of the presser foot in up position and the needle plate should be 6.0 mm.
Presser bar height
1. Remove the face plate and needle.
2. Lower the feed dog below the needle plate. Place a block 6 mm thick under the presser foot and lower the
presser foot lifter.
3. Loosen the setscrew . Raise the presser foot lifter and tighten the setscrew firmly.
Attach the needle and face plate.
NOTE:
Make sure that the presser foot should be parallel to the feed dog slots in the needle plate.
q
q
w
w
Presser foot should be
parallel to the feed dog slots.
q

10
0.2 mm
or more
0.2 mm
or more
Ａ=Ｂ
Mechanical Adjustment
Needle drop position
Set the stitch pattern to " ". The standard needle drop position should be at center of the needle plate hole .
Select zigzag stitch " ", and set the stitch width at " 5.0 ". The clearance between the needle and the edge of the
needle hole in the needle plate should be at least 0.2 mm on either side. If not, adjust as follows:
1. Remove the face cover. (See page 4.)
2. Turn the power switch on and check the needle drop position.
3. If the needle drop is out of position, adjust it to propper position by turning the adjusting screw " " so that
the needle is in the center of the needle hole when the straight stitch " " is selected.
4. Check the needle drop position of the zigzag stitch " " with the maximum width.
4. Attach the face cover.
NOTE:
Check the hook timing after this adjustment.
q
q
w
w

11
When the tip of the hook meets the left side of the needle in ascending travel of the needle from its left and lowest
position, the distance between the top of the needle eye and the tip of the hook should be in the range of 3.0 to 3.6
mm.
1. Remove the face cover, needle plate and bobbin holder.
2. Turn on the power switch.
3. Select the pattern (simple zigzag). (maximum zigzag width)
4. Turn the handwheel toward you until the tip of hook meets the right side of the needle.
5. Loosen the setscrew .
6. Adjust the height of the needle bar by moving the needle bar upward or downward without turning it. (Make sure
that the needle setting groove of the needle bar is in the front).
7. Tighten the setscrew .
8. Insert the bobbin holder, then attach the needle plate and face cover.
Needle #14 Hook race
3.0-3.6 mm
Upper edge of
needle eye
Hook race unit
Mechanical Adjustment
Needle bar height
q
q
w
w
w
e
e

12
When the machine is set for zigzag stitch (maximum zigzzag width) at the right needle position, the
amount of ascending travel of the needle bar from its lowest position at the right needle drop to the
position where the tip of the hook meets the right side of the needle should be 1.4 – 2.0mm.
1.Remove the needle plate and bobbin holder.
2.Turn on the power switch, select the pattern (simple zigzag). (maximum zigzag width)
3.Remove the bed cover.
4.Turn the handwheel toward you, and set the needle bar at the lowest position.
5.Loosen the setscrews on the lower shaft timing gear .
6.Raise the needle bar 1.6 mm from the lowest position of the needle bar.
7.Turn the lower shaft timing gear until the tip of hook meets with the right side of needle.
8.Tighten the setscrews on lower shaft timing gear.
9.Attach the bed cover, bobbin holder and needle plate.
Needle #14
1.4–2.0 mm
Lowest needle
position
Mechanical Adjustment
Needle to hook timing
q
q w
w
e
e

13
Preparation:
1. Remove the needle plate, bobbin holder, and bed cover, and replace the needle with the test pin .
2. Turn the power switch on, and select pattern (simple zigzag). (maximum zigzag width)
Adjustment procedure:
1. Loosen the screws , , , then slightly tighten the hinge screw .
2. Turn the handwheel toward you to bring the hook point behind the needle. Adjust the clearance between the test
pin and the point of the hook in the left and right needle position to –0.1 to +0.05 mm by moving the hook
set plate up or down.
3. Tighten the setscrews , , .
4. Check the backlash of the hook, gear and lower shaft gear. (See. page 14).
5. Attach the bed cover, needle plate and bobbin holder, and remove the test pin.
* The clearance between the needle and the point of hook should be –0.1 to +0.05 mm.
–0.1 to +0.05 mm
Clearance between Needle and Hook Point
Mechanical Adjustment
q
q
w
w
e
e e
q w
r
r
e
t
t
y
y
r

14
To check
1. Turn the power switch off.
2. Remove the needle plate and bobbin holder.
3. Turn the handwheel slowly toward you until the tip of the hook is between both ends of feed dog .
4. Rock the hook race with fingers to check the rotary play. It should be within 0.8 mm.
*If there is more than 0.8 mm play, adjust as follows.
Adjustment procedure:
1. Remove the bed cover and loosen the setscrew .
2. Turn the lower shaft bushing (eccentric) , in the direction " E " when the play at hook tip is too small.
3. Turn the lower shaft bushing (eccentric) , in the direction " F " when the play at hook tip is too large.
4. Tighten setscrew securely after adjustment.
Check the play.
E
F
Groove of lower shaft bushing (D)
Lower shaft gear
E
F
Mechanical Adjustment
Backlash ( Lower shaft gear )
q
q w
w
e
e
r
r
r
e

15
The highest position of the feed dog should be between 0.80 and 0.90 mm from the surface of the needle plate.
1. Remove the bed cover.
2. Turn the power switch on.
3. Select the straight stitch pattern with maximum length.
4. Turn the handwheel toward you to set the feed dog at the highest position.
5. Loosen the setscrew and nut .
6. Adjust the feed dog height by turning the adjusting screw .
7. Tighten the nut and setscrew .
E (To raise)
D
(To lower)
Presser foot
Feed dog
0.80-0.90mm
Surface of the needle
plate
Feed dog height
Mechanical Adjustment
q
q
w
w
e
e
w q

16
1. Remove the front cover (Refer to page 6-7).
2. Turn on the power switch, select the pattern " ", and set the machine at the maximum zigzag width.
3. Turn the handwheel toward you slowly with your hand until the needle start to swing. Loosen the setscrew
and turn the upper shaft shield plate in the direction of:
A: If the swing point is higher than 7.5 mm.
B: If the swing point is lower than 6.3 mm.
4. Shift the upper shaft shield plate to the left as close to the upper shaft sensor as possible.
(It should not touch the upper shaft sensor ).
5. Check the swing point by turning the handwheel, then tighten the setscrew.
6. Attach the front cover.
The needle should start to swing between 6.3 and 7.5 mm above the surface of the needle plate when the machine
is set for zigzag stitching.
Needle #14
6.3–7.5mm
Surface of the needle plate
A
B
Needle swing timing
Mechanical Adjustment
q
q w
w
e
e

17
4
3
5
(B)
()
Mechanical Adjustment
Top tension
The top tension should be between 75 and 90g when pulling the thread up in the direction of C.
* Use polyester sewing thread #50 (White).
* If it is not within the above limit, adjust as follows.
1. Set the tension dial at "4".
2. Lower the presser foot.
3. Remove the front cover unit (See P.6 – 7).
2. Pull the spring away from the lead screw .
3. If the top tension is too loose, turn the lead screw in the direction (A).
4. If the top tension is too tight, turn the lead screw in the direction (B).
Pull this way
q
w
e
e
C
w
e
e
q

18
1. Set the machine to the adjustment mode (See illustration below).
2. Set the slit of the feed balancing dial at the standard setting mark '' '' on the front cover.
3. Enter the adjusting mode. Sew the stitch pattern "8" until the machine stop automatically, and check the stitch
length.
* Standard length of five "8" characters: 32 mm – 40 mm
4. Remove the base cap .
5. If the length is too short, turn the adjusting screw in the direction of (D).
6. If the length is too long, turn the adjusting screw in the direction of (C).
7. Attach the base cap.
When a stretch pattern is sewn with the feed balancing dial set at the standard setting mark '' '' , The pattern
should be as indicated with the '' '' mark in the figure below. (If the stitch feed is not balanced, adjust it as follows:
F
START
STOP
START
STOP
(Enter the adjustment mode)
Turn the power switch on
while pressing the Up/Down
button and S/S button at the
same time.
The LED display
indicates "1". Press the needle Up/Down button.
▲
36±4mm
CD
Stretch stitch feed balance
Mechanical Adjustment
▲
q
q
w
w
w
e
e
r
r
r
q