Bosch TCA640 Series Repair Instruction page 33

4.3.4 Compensation of the grinding unit running time
The amount of ground coffee which is generated by the grinding unit
depends on the running time of the grinding unit.
To ensure that the required amount of coffee is always ground, both
with different types of coffee, at different grinding settings and possibly
with worn grinding tools, the amount of ground coffee which was
actually conveyed to the brewing module (B) is measured.
The more powder there is in the brewing chamber, the higher the
spring-mounted brewing head is pushed upwards during compression.
A micro switch (µ) closes and opens as it moves past via a slide which
is connected mechanically to the brewing head.
58300000120060_ARA_en_c.doc – 18.09.09
The electronics module measures the number of the voltage changes
(connection A) caused by the switching processes which occur
immediately before the pressure pump switches on and can therefore
detect whether and how much ground coffee has been metered. This
value can be compared with the nominal value for the aroma setting.
Differences are adjusted by changing the running times of the grinding
unit.
4.3.4.1 Switching states
If there is a minimum amount of coffee (<7 g), the brewing head
does not move. The switch is not actuated. = Not enough coffee
beans. ADD BEANS is displayed
(I) Amount of powder >7 g – <10 g
(II) Amount of powder 10 g
(III) Amount of powder >10 g – <13 g
(IV) Amount of powder >14 g = Too many coffee beans. The
running time of the grinding unit must be reduced.
Special cases:
Too hot and too little
powder before brewing
st
Too little powder during 1
brewing process
Brewing is ended (dry discharge),
there is no pumping. The brewing
module moves to the
position. Auto cooling starts (several
ml of water are conveyed) and
SYSTEM TOO HOT is displayed
ADD BEANS is displayed and an
additional time of 1.3 sec. is given.
Compensation is not active during
this and the next brewing process.
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grinding