Bernina arista 165 Service Manual page 26

Description of the electronics
25
The electronics of the BERNINA artista are basically con-
tained in two modules (printed circuits), namely on the
power L-print and the S-print (see block diagram).
Power L-print
The power L-print is mounted at the rear of the sewing
machine. The circuits have the following functions:
Motor control
The motor control for the main motor operates with low
safety voltages. The main motor is a 30 volt DC motor,
the speed of which is controlled by a pulse width modu-
lation. The regulating circuit is integrated at the control
side (S-print). All circuits for the motor control work with
low safety voltages.
Power supply
The following voltages are supplied:
· 5 V for the logic on the S-print
· 12 V for the sewing light
· 30/33 V for the drive motor, bobbin winder motor and
stepping motors.
In case of malfunction, a T-3A fuse protects the parts against
overload. If a fuse blows, only an original replacement with the
correct ratings must be used.
S-print
The S-print is assembled with the latest SMD (Surface
Mounted Unit) technology. SMD components allow a
very compact type of circuitry.
SMD prints cannot be repaired with conventional tools!
The micro-computer on the S-print receives an analogue
signal from the foot control which is converted into a
digital signal and given as a nominal value.
When the foot control is released (nominal value zero)
the micro-computer switches on the electric brake.
The motor is stopped very quickly in the required needle
position. The signal exchange between the S-print and
the L-print is carried by means of a 5-pole cable (165-
180).
When the sewing machine is switched on the stepping
motors are in any given position. There can also be any
given value in the memory of the micro-computer.
So that a defined basis is achieved, the stepping motors
are positioned by means of a signal from the micro com-
puter. This position is then registered and set at zero in
the memory of the micro-computer. It is then possible to
select and sew any given stitch from this zero position.