Janome JP720 Servicing Manual
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Janome JP720 Servicing Manual

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SERVICING
MANUAL
JP720 & JP760

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Summary of Contents for Janome JP720

  • Page 1 SERVICING MANUAL JP720 & JP760...

  • Page 2: Table Of Contents

    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 ...............................

  • Page 3: What To Do When

    What to do when Condition Cause How to fix Reference 1. Skipping 1. Needle is not inserted properly. Insert the needle properly. Stitches 2. Needle is bent or worn. Change the needle. 3. Incorrectly threaded. Rethread. 4. Needle or thread are Use the recommended sewing needle and inappropriate for fabric being thread.
  • Page 4 Condition Cause How to Fix Reference 3. Breaking 1. Initial sewing speed is too fast. Start with medium speed. uper thread. 2. Thread path is incorrect. Use the proper thread path. 3. Needle is bent or dull. Replace with a new needle. 4.
  • Page 5 Condition Cause How to fix Reference 6. Noisy 1. Backlash between hook gear and See mechanical adjustment P. 14 operation lower shaft gear is too great. “backlash (lower shaft gear)”. 2. Lower shaft gear is loose. Eliminate the looseness. 3. Inappropriatte belt tension. See part removal and replacement P.

  • Page 6: Changing External Parts

    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...

  • Page 7: Bed Cover

    Changing External Parts Bed cover 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.

  • Page 8: Front Cover

    Changing External Parts Front cover 1. Remove the face cover. (See page 4) 2. Loosen the set screw then remove the set screw 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.
  • Page 9 Changing External Parts Front cover 4. Disengage the hooks and stitch balance adjustment knob 5. Remove the front cover. To attach: Follow the above procedures in reverse.
  • Page 10 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.

  • Page 11: Mechanical Adjustment

    Mechanical Adjustment Presser bar height The distance between the bottom of the presser foot in up position and the needle plate should be 6.0 mm. 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.

  • Page 12: Needle Drop Position

    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.

  • Page 13: Needle Bar Height

    Mechanical Adjustment Needle bar height 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 1.

  • Page 14: Needle To Hook Timing

    Mechanical Adjustment Needle to hook timing 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 –...

  • Page 15: Clearance Between Needle And Hook Point

    Mechanical Adjustment Clearance between Needle and Hook Point * The clearance between the needle and the point of hook should be –0.1 to +0.05 mm. Preparation: 1. Remove the needle plate, bobbin holder, and bed cover, and replace the needle with the test pin 2.

  • Page 16: Backlash ( Lower Shaft Gear )

    Mechanical Adjustment Backlash ( Lower shaft gear ) 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.

  • Page 17: Feed Dog Height

    Mechanical Adjustment Feed dog height 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.

  • Page 18: Needle Swing Timming

    Mechanical Adjustment Needle swing timing 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. 1. Remove the front cover (Refer to page 6-7). 2.

  • Page 19: Top Tension

    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.

  • Page 20: Stretch Stitch Feed Balance

    Mechanical Adjustment Stretch stitch feed balance 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: 1.

  • Page 21: Thread Plate

    Mechanical Adjustment Thread plate When the hook of the threader plate is damaged, change or adjust the part as follows. To change the threader plate: 1. Raise the needle to its highest position and lower the threader knob to its lowest position. 2.

  • Page 22: Replacing The Electronic Components

    Replacing the Electronic Components Location of the connectors NOTE: * Do not disconnect the connectors by pulling on the cord. * To disconnect, grasp the connector, not the cord. * Connect the connector to the connector post of the same color on the circuit board. Bobbin winder switch BH sensor Machine socket...
  • Page 23 Self-diagnostic Test Preparation: 1. Turn the power switch. 2. Move the bobbin winder spindle to the left. 3. Raise the feed dog. 4. Set the speed control lever to the left. 5. Remove the presser foot and raise the presser foot lifter. 6.
  • Page 24 Step and Procedure Correct Condition Defective condition items to check Turn on the power switch while simulta- Beeping sound when the button pressed. No beep sound neously pressing the needle up/down LED display "8.8". And it blinks in one Does not enter self- segmentLED button and start/stop button.
  • Page 25 Step and items Correct Condition Procedure Defective condition to check When the needle is at Press the needle up/down button, LED display is different from that the highest position, LED Upper shaft LED dispays "07" for one second. shown to the left. displays "H.L".

  • Page 26: Circuit Board-A

    Replacing the Electronic Components Circuit board-A To remove: 1. Remove the front cover. (See pages 6 – 7) 2. Pull out connectors from the circuit board-A. 3. Loosen 7 screws and remove the circuit board-A. To attach: 1. Follow the above procedures in reverse. NOTE: Do not disconnect the connectors by pulling on cord.

  • Page 27: Circuit Board-F

    Replacing the Electronic Components Circuit board-F To remove: 1. Removed the front cover. Pull out the circuit board-F connector , from the circuit board-A 3. Loosen the set screw and remove the board-F To attach: 1. Follow the above procedures in reverse. NOTE: * Insert the lower part of the board-F into the hole of rear cover when attaching the board-F.

  • Page 28: Driving Motor

    Replacing the Electronic Components Driving motor To remove: 1. Remove the front cover and the rear cover. 2. Loosen 2 screws and remove the driving motor and the belt To attach: 1. Install the driving motor and the motor belt with 2 screws 2.
  • Page 29 Replacing the Electronic Components Switching regulator unit To remove: 1. Remove the front cover and the rear cover. 2. Loosen 2 screws and a screw , then remove the switching regulator To attach: 3. Follow the above procedures in reverse. NOTE: * Cords should not contact the lower shaft, motor belt etc.

  • Page 30: Stepping Motor ( Zigzag )

    Replacing the Electronic Components Stepping motor ( Zigzag ) To remove: 1. Remove the front cover and the rear cover. 2. Remove 2 screws 3. Remove E-ring 4. Remove stepping motor (Zigzag). To attach: 1. Follow the above procedures in reverse. NOTE: * Check the needle drop position after replacing the stepping motor.

  • Page 31: Stepping Motor ( Feed )

    Replacing the Electronic Components Stepping motor ( Feed ) To remove: 1. Remove the front cover and the rear cover. 2. Remove 2 screws 3. Remove E-ring 4. Remove stepping motor (Feed). To attach: 1. Follow the above procedures in reverse. NOTE: * Check the stretch stitch balance after replacing the stepping motor.

  • Page 32: Buttonhole Lever Guide

    Mechanical Adjustment Adjusting buttonhole lever position To adjust the buttonhole lever guide: 1. Enter the buttonhole sensor adjusting mode. (See below. The LED should display " H " or " L ".) 2. Remove the face cover (see page 4) and loosen set screw 3.

  • Page 33: Oiling

    Oiling Factory lubricated parts will provide years of household sewing without routine oiling. However, whenever the machine is being serviced, check to see if any parts need to be luburicated. OIL: Use good quality sewing machine oil at the points ( A, B, C, D, E, F, G, H, J, K ) indicated by black arrows. Grease White grease is recommended for use on gears and cam surfaces.

This manual is also suitable for:

Jp760

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