Baby Lock BL7800 Manuale utente

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4. 2001.

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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.

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I. PRINCIPAL MECHANISMS..................................................................................1

II. DISASSEMBLING AND REASSEMBLING THE SEWING MACHINE................7

III. HOW TO ADJUST MECHANICAL ELEMENTS.................................................20

IV. HOW TO ADJUST ELECTRONIC ELEMENTS.................................................37

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1. Always use rubber gloves when handling printed circuit boards and never touch the metal portion of a printed

circuit board with bare hands.

2. Keep your bodyearthed in order to avoid generating static electricity.

3. Pack printed circuit boards in aluminum foil and avoid subjecting them to anyform of impact during storage or

transportation.

4. Do not touch or damage the metal portion of a printed circuit board with a screwdriver or anyother tool while

making repairs or the like.

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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

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1. MECHANICAL CHART

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2. POWER TRANSMISSION CHART

(A) Generating mechanism of needle bar, thread take-up lever and zigzag movements

(B) Mechanism of feed dog and rotary hook movement

Upper shaft

Balance wheel

ZPM

(Zigzag pulse motor) Needle bar crank rod

Needle bar clamp

Needle bar supporter

Zigzag connecting rod

Needle bar Needle

Balance wheel

Upper shaft

Horizontal cam pulley

Timing belt

FPM

(Feed pulse motor)

Timing pulley D

Vertical feed cam

Rotary hook assembly

Feed stand Feed dog Drop plate

Lower shaft Side feed plate spring

Horizontal feed arm

Lower shaft gear Horizontal feed plate Horizontal feed shaft

Side feed plate

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3. ELECTRONIC PARTS ARRANGEMENT CHART

NP (needle position) PC board switch

PF (Presser foot)

switch

SS (start/stop)

PC board

ZPM

(zigzag pulse motor)

(buttonhole) switch

BHL

(buttonhole lever)

switch

WB light

(Lamp)

VR PC

board

Power supply unit

Main PC

board

Inlet assembly

(foot controller

jack)

Power supply

switch

FPM

(feed pulse motor)

Operation

panel

Operation PC

board

BW (bobbin winder) switch

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4. CONTROL SYSTEM BLOCK DIAGRAM

Control system block diagram

5. 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.

6. PATTERN GENERATOR

For conventional sewing machines, the pattern was generated by rocking the needle bar and the feed regulator by

means of a pattern cam onto which the pattern data had been mechanically engraved. In contrast to this, this model

stores the data electronically in memory and uses a feed pulse motor, and a zigzag pulse motor to directly rock the

needle bar and the feed regulator to generate the pattern. In addition, the pulse motors must move the position of

the needle while the needle is raised and stop it in the correct position (and similarly, they must move the position of

the feed regulator while the needle is lowered). Thus, highly-precise positioning and a fast response speed are

required. Because of this, the feed pulse motor, and a zigzag pulse motor were adopted, and a simple open-loop

structure circuit was employed.

Block diagram of pattern generator control

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7. 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. For lockstitching,

three stitches are made at the current needle position and then sewing stops.

Needle position (NP) switch ................used to change the needle position either up or down.

Operation panel...................................used to select pattern required for sewing. This simplifies the operation for

selecting the desired pattern.

Buttonhole(BH) stitch switch................used to detect the edges of the buttonhole stitch by means of the buttonhole

stitch presser foot and lever.

Buttonhole stitch lever(BHL) switch.....used to detect whether the buttonhole stitch lever is raised or lowered.

Needle position(NP) sensor.................detects the drive timing of zigzag and feed pulse motors and detects the

(Rotation Sensor) vertical position of the needle. Also detects the turning angle of the upper

shaft by means of a photointerruptor and shutter installed on the upper shaft.

Speed sensor ......................................used to detect the rotation speed of the main motor.

detects the operating speed of the main motor by means of a

photointerruptor and shutter installed on the upper shaft.

Bobbin winder(BW) switch ..................used to detect whether the bobbin winder has been set when winding the

lower thread.

Presser foot(PF) switch.......................used to detect whether the pressor foot is raised or lowered.

Foot controller jack..............................when using the foot controller, connect it to this terminal.

Transformer.........................................used for driving the pulse motors, to illuminate the lamps and to supply

power to the electronic circuitry.

WB light (Lamp)...................................is 12V 5W.

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1.DISASSEMBLING AND REASSEMBLING

THE OUTER PARTS AND MAIN PARTS................................................................8

2.LEAD WIRE ARRANGEMENT..............................................................................19

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1. DISASSEMBLING AND REASSEMBLING THE OUTER PARTS AND MAIN

PARTS

1. Remove the screw securing the face plate, and the face plate by sliding it to the left.

2. Remove the screw securing the free arm cover, and the free arm cover by sliding it to the left.

3. 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.

4. Remove the two screws securing the base cover, slide the base cover to the left and then holding the front,

slide it to the left and out.

5. Remove the screw securing the front cover (near spool pin), and loosen the two screws (below jaw section on

face plate side, below free arm). Open the front cover toward the front, remove the three connectors and then

the front cover.

6. Remove the two screws securing the needle plate, and the needle plate.

7. Remove the three screws securing the rear cover, and the rear cover from the rear side.

Disassembly Points

3. To remove the belt cover, unhook the bottom catch (A), slide the belt cover to the right, then unhook the top

catches (B) by sliding the belt cover downward.

5. To remove the front cover, slide part (C) downward, unhook the two catches (D) from the base plate and the

jaw section of the front cover (E) from the bottom of the thread guide, then pull the front cover away at the

front.

7. To remove the screw (F) securing the rear cover, move the bobbin winder shaft to the right.

* Before removing the rear cover, lower the presser foot lifter.

Indice

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