Roche Diagnostics April 2007
Service manual · Version 2.0 A-35
91xx pH/Electrolyte Analyzers 4 Description of modules
Description of modules
Display board
The display board contains the LCD display, sample contact circuit (9110 only) or
sample sensor connector, the preheater (9110 only) and the YES and NO switches
used for operation of the analyzer. Power and signal interconnection is accomplished
via a ribbon cable from the SBC board through JP2 on the display board.
9110 only The sample contact circuit consists of a square wave generator U1B which generates a
500 Hz signal. U1A amplifies the signal, D2 and C3 rectify the square wave. The gain
can be adjusted with R10. The sample contact output provides a DC voltage, which is
proportional to the square wave amplitude. During sample aspiration, the preheater
tube and the sample contact 1 tube are connected to the square wave via relay K1.
The heater control circuit controls two transistors which are placed in the preheater
block. A thermistor provides temperature feedback to the setting of potentiometer
R20. The signal difference drives the base of the heating transistors via buffer U2C.
U2D shuts the system off in case the thermistor opens. U2B limits the maximum
heating current during warm-up. U1C and attached circuit is used as an AC/DC
converter to create negative voltage -V
SS
, using square wave generator U1B.
9181 only Display boards utilized in the 9181 analyzer also contain circuitry for both the needle
mechanism motor control and position sensor. The autosampler "Table Present"
signal is also buffered through U1 on this board.
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