Janome 4300QDC User manual

First Edition: 19 September 2018
SERVICE MANUAL
MODEL: 4300QDC

INDEX
What to do when.................................................................................................................................. 1-3
Changing External Parts
Face Cover............................................................................................................................................. 4
Free arm Cover ..................................................................................................................................... 5
Front Cover.......................................................................................................................................... 6-7
Rear Cover ............................................................................................................................................. 8
Mechanical Adjustment
Presser Bar Height ................................................................................................................................. 9
Needle Drop Position............................................................................................................................ 10
Adjustment of Hook Timing....................................................................................................................11
Adjustment of Needle Bar Height ......................................................................................................... 12
Clearance between Needle and Tip of Rotary Hook ............................................................................ 13
Feed Dog Height .................................................................................................................................. 14
Top Tension .......................................................................................................................................... 15
Stretch Stitch Feed Balance................................................................................................................. 16
Replacing the Electronic Components
Circuit Board-A Connection .................................................................................................................. 17
Self-diagnostic Test ......................................................................................................................... 18-23
Circuit Board-A ..................................................................................................................................... 24
Driving Motor ........................................................................................................................................ 25
Switching Regulator Unit ...................................................................................................................... 26
Adjusting Buttonhole Lever Position..................................................................................................... 27

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 the fabric
being sewn.
5. Sewing on stretch fabric.
6. Inappropriate needle bar height.
7. Inappropriate needle to hook
timing.
8. 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.
See mechanical adjustment “Needle bar
height”.
See mechanical adjustment “Adjustment
of hook timing”.
See mechanical adjustment “Clearance
between needle and tip of the rotary
hook”.
P. 12
P. 11
P. 13
2. Fabric not
moving
1. Incorrect feed dog height.
2. Feed dog is in down position.
3. Thread on bottom side of
fabric is jammed up.
4. 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
bobbin threads under the foot when start
sewing.
Change the feed dog.
P. 14
What to do when

2
Condition Cause How to Fix Reference
3. Breaking
upper
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.
Repair the hole or replace the needle
plate.
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
breaks
1. Needle is hitting the needle plate.
2. Needle is bent or worn.
3. Needle is hitting the hook.
4. Fabric is being pulled too strongly
while sewing.
See mechanical adjustment “Needle drop
position”.
Change the needle.
See mechanical adjustment “Clearance
between needle and tip of the rotary
hook”.
Guide the fabric gently while sewing.
P. 10
P. 13

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. Inappropriate belt tension.
4. Not enough oil.
5. Upper shaft gear is loose.
Eliminate the backlash.
Eliminate the looseness.
See part removal and replacement
“driving motor (DC motor)”.
Oil all moving parts.
Eliminate the looseness.
P. 25
7. Deformation
pattern
1. Inappropriate feed balance.
2. Top tension is too strong.
Adjust the feed balancing screw.
See mechanical adjustment
“Top tension”.
P. 16
P. 15