Baby Lock BL7800 User manual

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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)
BH
(buttonhole) switch
BHL
(buttonhole lever)
switch
WB light
(Lamp)
VR PC
board
Power supply unit
Main PC
board
Inlet assembly
FC
(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.