Service manual

Section - VII Reagent Module BT3000 PLUS Rev. 0, Soft Ver. 8 Page 2 of 6
The gate P0.7 of µC U3 sends the command bit of optoisolator U8 (TLP521-1). A low
logic level of P0.7 determines the simultaneous opening of the MOSFETs Q1 and Q2
(BUZ111S) and the consequent inhibition of the peltier modules of the refrigeration
system.
The gate P1.6 of U3 controls the high velocity optoisolator U9 (6N136). This optoisolator
drives the digital potentiometers PD1 and PD2. The potentiometers through their ohmic
variation determine the Peltier supply voltage value. An approximate voltage of 26VDC
corresponds to the higher cooling capacity and the approximate voltage of 16VDC
corresponds to the lower cooling capacity. The power supply is interfaced through the
connector J2. The NTC1 sensor protects the reagent controller module against
overheating. The high temperature inside the module (>70ºC) produces a voltage
variation on the gate P0.6 of U3. The intervention threshold is fixed at 4.5V. During the
alarm condition the Peltier modules are disabled and an alarm message is displayed on
the analyzer screen.
The gate P0.0 of U3 drives the optoisolator U11 (TLP521-1). The low level logic of P0.0
determines the opening of the transistor Q3 and the power off to the cross blower
ventilator. The operating logic turns the cross blower fan ON or OFF when the reagent
plate reaches the preset temperature (±0.5º) in the analyzer setup to avoid ice formation
in the reagent plate with ambient temperature up to +12ºC (values beyond the operating
range).
The glowing LED (DL5) indicates the activation of cross blower fan.
This board, compared to the previous board, has the advantage of functioning also when
the analyzer is in the standby mode, without any supply voltage from the IBM.
The supply voltage for the µC 767 is realized on board through a DC/DC converter, which
is powered by the same source that energizes Peltiers. The temperature sensor is
connected to the gate A/D of the 764 for reading the value in ºC. The temperature
monitoring system is controlled digitally by regulating nominal 24V in the range of 16V to
28 Volts.
Below a certain temperature (approximately 5ºC), it is not possible to further reduce the
current of the Peltiers. Therefore to control the temperature, the operation of cross-blower
fan is interrupted for the time necessary to reset the selected temperature. The
temperature is selected in the instrument setup and the temperature can be set between
5ºC and 15ºC. The set temperature is maintained reagent chamber base to a tolerance of
+/-2°C as long as the ambient temperature does not exceed the 26ºC. Beyond 26ºC it is
possible to have a considerable increase in the set temperature. If the µC reads a
temperature higher than approximately 40ºC, then it interrupts the current to the
regulation circuit assuming that there is a problem in the system. For example a defective
or damaged fan or an exceptionally high ambient temperature (40ºC) may generate an
excessive temperature in the reagent chamber. One can observe in the electrical
schematic the NTC near the power connectors. It has the function of heat sensor, which
may be produced by false contacts in the connections or some other problems in the
printed circuit board. In this case the MOSFET Qx interrupts the Peltier current, when the
temperature in the interested zone is approximately 70ºC.