Douwe Egberts Cafitesse 100, Service Manual, Page: 148 / 210

07.2004
5C - 10
Functions - Dosing System Service Manual Cafitesse 100
• The secondary voltage of a 25 V
transformator is rectified by a bridge
rectifier and smoothened by a diode and a
condensator. The smoothened voltage is
stabilised at 20.5 V by a voltage regulator.
(Fig. 1)
• The green LED on the pc board indicates
that the 20.5 V supply is applied.
• Pulses are transmitted to the coil when the
delivery button has been actuated. Each
pulse enables the delivery of 0.105 cc.
• The microprocessor controls the pulse
duration and the intervals.
a) Pulse current and pulse duration:
• Pulses are generated when the concentrate
coil is triggered by the microprocessor via
two transistors and is switched off again at
a coil current of 5.2 A. The current is
measured by measuring the voltage at a
measuring resistor.
U
--- = 5.2 A
R
• In normal operation the pulse duration is
6.7 msec. When the pulse duration is not
between 6.5 msec. and 10 msec., the error
message 'Error last dosing' is indicated.
This can only be read out by means of the
Service Device.
The microprocessor switches the
transistors off after a maximum pulse
duration of 10 msec., even when the
peak current value has not been
reached. Dosing is still posible when
the circuit is not interrupted, but it is
not exact.
Special equipment and indicator circuit
• The indicator and special equipment are
supplied by the concentrate coil circuit.
The stabilised 20.5 V supply is regulated at
5 V by means of a resistor and a voltage
regulator to supply future special
equipment. The microprocessor transfers
the counter data to the indicator.
Fig. 1
main
switch
fuse
trans-
formator
T02
mains
bridge rectifier
condensator
20.5 V
concentrate
coil
switching
transistor
measuring
resistor
0.22 Ω
delivery
button
MP
C.4 Electrical Diagrams
C.4.1 Circuit of the concentrate coil
diode
voltage regulator
switching
transistor
F05