Baby Lock BL7800 Service Manual
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Baby Lock BL7800 Service Manual

Baby Lock BL7800 Service Manual

Computerized sewing maachine
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2001
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Summary of Contents for Baby Lock BL7800

  • Page 1 2001...
  • Page 2 This service manual has been compiled for explaining repair procedures of BL7800. This was produced based on up-to-date product specifications at the time of issue, but there may have been changes of specifications for the purpose of improvements. Contact manufacturer or local sales company for information concerning such changes.

  • Page 3: Table Of Contents

    1. MECHANICAL CHART..................2 2. POWER TRANSMISSION CHART...............3 3. ELECTRONIC PARTS ARRANGEMENT CHART..........4 4. CONTROL SYSTEM BLOCK DIAGRAM.............5 5. MOTOR UNIT CONTROL..................5 6. PATTERN GENERATOR..................5 7. OTHER ELECTRONIC COMPONENT FUNCTIONS ...........6 - 1 -...

  • Page 4: Mechanical Chart

    MECHANICAL CHART - 2 -...

  • Page 5: Power Transmission Chart

    POWER TRANSMISSION CHART Generating mechanism of needle bar, thread take-up lever and zigzag movements Balance wheel Upper shaft Needle bar crank rod (Zigzag pulse motor) Needle bar clamp Zigzag connecting rod Needle bar supporter Needle bar Needle Mechanism of feed dog and rotary hook movement Balance wheel Upper shaft Horizontal cam pulley...

  • Page 6: Electronic Parts Arrangement Chart

    ELECTRONIC PARTS ARRANGEMENT CHART PF (Presser foot) switch BW (bobbin winder) switch SS (start/stop) PC board NP (needle position) PC board switch Operation PC board Operation (zigzag pulse motor) panel Main PC board (buttonhole) switch (buttonhole lever) (feed pulse motor) switch VR PC Power supply...

  • Page 7: Control System Block Diagram

    CONTROL SYSTEM BLOCK DIAGRAM Control system block diagram MOTOR UNIT CONTROL The main motor for the sewing machine is required to smoothly change from low speed to high speed without any fluctuations due to load or temperature changes. To fully comply with this requirement, this model adopts PWM control using FET.

  • Page 8: Other Electronic Component Functions

    OTHER ELECTRONIC COMPONENT FUNCTIONS Start/stop(SS) switch ......used to start and stop (SS) the machine. If you want to start sewing at low speed, keep this switch depressed and start sewing. Backstitch(BK) switch ......used for backstitching and lockstitching. Backstitching is performed at low speed in the reverse direction while the switch is pressed.
  • Page 9 1. DISASSEMBLING AND REASSEMBLING THE OUTER PARTS AND MAIN PARTS..............8 2. LEAD WIRE ARRANGEMENT................19 - 7 -...
  • Page 10 DISASSEMBLING AND REASSEMBLING THE OUTER PARTS AND MAIN PARTS Remove the screw securing the face plate, and the face plate by sliding it to the left. Remove the screw securing the free arm cover, and the free arm cover by sliding it to the left. Remove the blind cap on the belt cover, the screw securing the belt cover, and the belt cover from below by sliding it to the right.
  • Page 11 8. Remove the presser holder and needle. 9. Remove the 8 connectors, the two screws, and the main PC board. 10. Remove the two screws and handle holder assembly. 11. Remove the screw and the bobbin winder switch assembly. 12. Remove the motor belt and pull out the motor connector. Remove the two screws and the motor unit. 13.
  • Page 12 19. Remove the two screws and the lower thread guide assembly. 20. Remove the screw and the inner rotary hook bracket. 21. Remove the presser bar clamp screw. 22. Remove the presser bar by lifting it from above, and the presser bar clamp. 23.
  • Page 13 26. Remove the two screws securing the upper shaft metal, and the upper shaft assembly. 27. Remove the screw and the NP PC board assembly. 28. Remove the screw and the tension pulley holder. 29. Remove the two feed rod tension springs. 30.
  • Page 14 38. Install the tension releaser plate onto the pin, then install the CS retaining ring. 39. Attach the bace plate using the three screws. 40. Attach the power supply unit assembly using the two screws, and insert the inlet connector. 41.
  • Page 15 - 13 -...
  • Page 16 50. Attach the thread take-up shaft using the screw. 51. Attach the presser spring using the collar and screw. 52. Insert and attach the presser foot lifter using the presser lifter shaft. 53. Insert and attach the presser bar into the presser bar clamp. 54.
  • Page 17 - 15 -...
  • Page 18 57. Attach the ZPM holder assembly using the two screws. 58. Attach the needle bar supporter assembly using the two springs. (Insert the needle bar clamp into needle bar crank rod.) 59. Attach the needle bar supporter stud holder using the screw. (Insert the needle bar block arm into the pin on the needle bar block.) 60.
  • Page 19 - 17 -...
  • Page 20 68. Attach the rear cover using the three screws. 69. Attach the needle plate assembly using the two screws. 70. Connect the three connectors, and attach the front cover using the three screws. 71. Insert the base cover into the base plate and attach using the two screws. 72.
  • Page 21 LEAD WIRE ARRANGEMENT - 19 -...
  • Page 22 1. SETTING THE TEST MODE................21 2. TENSION OF MOTOR BELT AND TIMING BELT..........22 3. NEEDLE DOWN POSITION ADJUSTMENT............23 4. TIMING OF NEEDLE AND ROTARY HOOK (CLEARANCE BETWEEN THE NEEDLE AND THE ROTARY HOOK POINT)..24 5. NEEDLE BAR HEIGHT..................25 6. LOWER SHAFT ....................26 7.

  • Page 23: Setting The Test Mode

    SEETING THE TEST MODE BASIC TEST MODES To set the test mode, turn on the power switch while holding down the start/stop button and backtack button simultaneously. The LED will light up, and you can enter each test mode by pressing the corresponding pattern key. The monitor sign LED will blink.

  • Page 24: Tension Of Motor Belt And Timing Belt

    TENSION OF MOTOR BELT AND TIMING BELT STANDARD There should be a 4-6 mm slack in the motor belt when the center of the motor belt is pressed with a force of 200g. There should be a 3-4 mm slack in the timing belt when it is pressed with a force of 200g. ADJUSTMENT Timing belt Loosen the screw of the belt adjusting pulley.

  • Page 25: Needle Down Position Adjustment

    NEEDLE DOWN POSITION ADJUSTMENT STANDARD Put the machine in test mode. When pattern , or is selected to decide the left, center, or right needle position, the needle should be positioned in the left or right part of the needle plate hole in the needle down position. ADJUSTMENT Put the machine in test mode.

  • Page 26: Timing Of Needle And Rotary Hook (Clearance Between The Needle And The Rotary Hook Point)

    TIMING OF NEEDLE AND ROTARY HOOK (CLEARANCE BETWEEN THE NEEDLE AND THE ROTARY HOOK POINT) STANDARD When the machine is in test mode and is selected, and the needle is raised 2.9 to 3.3 mm from its lowest position, the rotary hook point should be aligned with the outer circumference of the needle. The clearance between the needle (golden needle) and the rotary hook point should be 0.1 mm or less, and they should never touch each other .

  • Page 27: Needle Bar Height

    NEEDLE BAR HEIGHT STANDARD When the machine is in test mode and pattern is selected, and the balance wheel is turned so that the needle meets the rotary hook point, the clearance between the upper end of the needle eye and the bottom of the rotary hook point should be 1.0 to 1.4 mm.

  • Page 28: Lower Shaft

    LOWER SHAFT Attach the bushing presser L temporarily so as the center of lower shaft is positioned higher by 1 mm against the center of eccentric metal. Install the outer rotary hook, then turn the eccentric metal and make sure that there is no backlash on the gears.

  • Page 29: Height Of Feed Dog

    HEIGHT OF FEED DOG STANDARD When the balance wheel is turned to raise the feed dog to its highest position, the standard height of the feed dog above the needle plate should be 0.9-1.1 mm. ADJUSTMENT Turn the balance wheel to raise the feed dog to its highest position. Loosen the screw securing the vertical feed roller shaft.

  • Page 30: Presser Bar Height

    PRESSER BAR HEIGHT STANDARD The clearance from the needle plate top to the bottom of the presser bar should be 7.0-7.5 mm. ADJUSTMENT Raise the presser foot lifter. Loosen the screw of the presser bar guide bracket. Adjust the height of the presser bar by moving it vertically. Tighten the screw of the presser bar guide bracket.

  • Page 31: Position Of Buttonhole Switch Lever

    POSITION OF BUTTONHOLE SWITCH LEVER STANDARD When the buttonhole lever is lowered, the clearance of front part of buttonhole foot is 1.5 mm and the presser foot lever is lowered BH0 should touch BH1. ADJUSTMENT Turn on power switch and select pattern Fit the buttonhole foot (A).

  • Page 32: Bobbin Winder

    BOBBIN WINDER STANDARD The thread should be wound parallel to the bobbin and around about 75-85% of the bobbin at low speed. (A) The clearance between the bobbin winder switch and the bobbin winder assembly should be 0.5-1.0 mm. (B) ADJUSTMENT 1.

  • Page 33: Dial Tension

    DIAL TENSION STANDAD With the presser foot lowered and the thread tension dial set to "4", use polyester thread (#60) to check that the tension between the tension discs is 33 to 38 g. ADJUSTMENT Set the thread tension dial to "4", pass polyester thread (#60) between the tension discs, then lower the presser foot.

  • Page 34: Inner Rotary Hook Bracket Position

    INNER ROTARY HOOK BRACKET POSITION STANDARD When the inner rotary hook bracket and the rotary hook meet, the spring of the inner rotary hook bracket and the inner rotary hook should overlap each other by 1.9-2.1 mm. ADJUSTMENT Loosen the screw securing the inner rotary hook bracket. Adjust the position of the inner rotary hook bracket by moving it vertically and/or horizontally.

  • Page 35: Feed Adjustment (Vertical Feed)

    FEED ADJUSTMENT (VERTICAL FEED) STANDARD Put the machine in test mode, and with pattern , 100 stitches forward and 100 stitches from the back will meet. ADJUSTMENT Loosen the screw securing the pulse motor. Rotate the pulse motor and adjust the pattern. * Make sure not to contact the main PC board during the adjustment.

  • Page 36: Needle Threader

    NEEDLE THREADER USING THE NEEDLE THREADER 5. Do not turn the balance wheel when using needle There are a wide variety of different needles and sewing threader. machine threads available. The right ones should be 6. Do not lower the needle threader lever while the selected in accordance with the sewing conditions.

  • Page 37: Needle Threader (Exchange)

    NEEDLE THREADER (EXCHANGE) HOW TO EXCHANGE NEEDLE THREADER Remove the needle and lower the presser foot. Push down the needle threader and take it out. Place a new one so that the guide is immediately under the groove as shown in figure A . Push the needle threader all the way up so that the guide is fits into the groove.

  • Page 38: Needle Threader

    NEEDLE THREADER (CHECKING THE HOOK POSITION IN VERTICAL DIRECTION) Case A (Hook point is too high) Adjust needle threader position setter slightly down and check that the clearance between the top of hook and top of needle eye is 0 mm. Case B (Hook point is too low) Adjust needle threader position setter slightly up and check the clearance between the top of hook and top...
  • Page 39 1. When power is turned on, buzzer does not sound and the LED does not light up .......................38 2. After the power is turned on, pulse motors do not return to their home positions with respect to the needle position (Zigzag pulse motor when needle bar is raised and feed pulse motor when needle bar is lowered) ..38 3.

  • Page 40: Light Up

    ∗ You must turn off the power and remove the connectors from printed circuit boards before measuring resistance. ∗ Refer to the illustrations for check locations. PROBLEM CHECK REMEDY When power is If the voltage between both inlet terminals is Replace the power cord.

  • Page 41: Operation Of Main Motor Is Not Stable, Maximum Speed Operation Is Not Possible, Or Speed Cannot Be Adjusted

    Main motor does Is the presser foot lever lowered, or does the Replace the presser foot SW not run. presser foot switch operate correctly? assembly. Resistance at both ends of switch: Ω When switch is pressed ..1 or less ∞...

  • Page 42: Abnormal

    Vertical movement Are the resistances of both ends of each Replace the SS PC board Ω of the needle bar switch on the SS PC board either 1 or less assembly. ∞ and backstitch depending on whether the switch is on or operation are off? abnormal.
  • Page 43 Main PC board - 41 -...
  • Page 44 Power supply unit Power 120 Power 230 - 42 -...
  • Page 45 Operation board Other PC boards - 43 -...
  • Page 46 BL7800 T1010141...

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