Bernina 1090 - Description of Print L-1230; Print A-KAO

Description
The electronics of the model 1090 sewing
machine is essentially located on three large
printed circuit boards; the power print L-1230, the
control print S-KAO and the display print A-KAO
(compare to the block schematic diagram). The
tasks of the 3 units correspond to the the known
functions of L-4200, $-4200 and A-4200 prints
from the model 1130.
L-1230 power print
The L-1230 power print is mounted above the
motor on the rear side of sewing machine. The
circuit components on the 1-4200 have the follow-
ing functions:
= Motor control:
The main motor control operates with the mains
voltage. Тре main motor is о DC motor with
pulse-width modulated speed control. The
ја ed loop control circuit on ће small R-4200
is located on the power print.
м circuit components for the ‘motor control
operate at dangerous voltage levels.
The safely regulations must be адћегед о.
- Power supply:
Generates the following D.C. voltages:
— 30V for the step motors
= ` 5V for the logic circuitry on the 5-КАО and
А-КАО prints
— 6У forthe sewing light
— 30V for the bobbin winder motor
Components are protected from overload, in
the case of faults, by a fuse F150. На fuse
blows only original replacement fuses, with the
correct rating may be us
А-КАО display print
The display section is mounted directly behind the
operating control ponel. The display and ope-
rating control elements are soldered onto ће
L-shaped printed circuit.
Анте multiplex control allows the numerous
LEDs and control elements to be connected іо the
open loop control on the 5-КАО control print
using only 21 connection lines.
$-KAO control print
The complete sewing machine control is located
‘onthe S-KAO control print. The 5-КАО control
print is located on the A-KAO print from the rear.
The most important control element is the
microcomputer, and the power drive for the step
motors. A new feature over model 1130 is that the
bobbin winder motor is also controlled by the
microprocessor. The bobbin winder motor speed
сап now be controlled from the foot control.
The $220 service switch on print S-KAO ва
service aid. This switch hos two positions: normal
sewing operation, and service position. In the
service position, several buttons and diodes on
the display panel are assigned other functions.
This allows the service technician to execute
necessary adjustment and testing functions using
the display panel (refer to the special section
service programme). The service switch must
always be set into the sewing position for normal
sewing operations.
The microcomputer on print S-KAO receives on
а! from ће foot control, which it then
а digital signal and transmits to print
R-4200 as setpoint for the motor speed. The
R-4200 print controls the motor speed to 1
ied by the Sprint, using a setpoint -
omparison. When the foot control is
released, ће setpoint goes to zero, the brake is
actuated from the microcomputer on the S-print
via the R-4200 print, and the motor is rapidly
braked.
‘Signal transfer between the S-KAO and R-4200
printis realised using а 4-pole cable. Signal
transfer is realised through an opto-coupler pro-
viding electrical isolation and thus eliminating
dangerous voltage levels from the foot control
and the $-КАО control print.
‘The step motors are in random positions when
sewing machine is switched on. Random valves
соп also be in the microcomputer control
memory. In order to have а defined state, the step
motors ore rotated into their calibrated position
by а microcomputer command, and the position
value is set to zero in the microcomputer memory.
This starting state allows the selection ond sewing
of any stitch programme.