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Ref. 185040646 MR730/720/700/480 Technical Manual ¯ Revision F ¯ Issued March 2001
4.3 POWER BOARD
4.3.1 REVISION D/F PCBS
A bridge rectifier (D13 to D16) supplies power to the 5 V regulator Q7 mounted on the heat sink. This circuit is protected
by a 1 A fuse (F1) mounted on the circuit board. The 5 V negative supply stabilized by Q8, is derived from the voltage
doubling network D17, D18.
The Heater Wire (HHC) is controlled by triac Q9 which is mounted on the heat sink. Q9 is switched by the optoisolator
U11 which in turn is driven by Q10. Q10 is controlled directly from an output port of U4 on the control board.
The resistor R52 connected to the anode of Q9 provides a signal through (HHS) to U5d and U4. This signal, with
processor interpretation, provides the information to determine if the Heater Wire is connected or open circuit and also
the integrity of fuse F2, the 4 A fuse supplying power to the Heater Wire.
Triac Q11 (mounted on the heatsink) is controlled by optoisolator U12, which in turn is controlled by Q12, and HPC.
Transistors Q5 and Q6 are a RS232 level driver for the serial data interface.
4.3.2 REVISION H AND J PCBS
A bridge rectifier (D13 to D16) supplies power to the 5 V regulator Q7 mounted on the heat sink. This circuit is protected
by a 1 A fuse (F1) mounted on the circuit board. The 5 V negative supply stabilized by Q8, is derived from the voltage
doubling network D17, D18.
The Heater Wire (HHC) is controlled by triac Q9 which is mounted on the heat sink. Q9 is switched by the optoisolator,
U11, which in turn is driven by Q10. Q10 is controlled directly from an output port of U4 on the control board (HHC).
Resistor R9, C6 form a snubber on the triac. Capacitors C8, C32 balance the heater wire with respect to ground.
Heater wire sensing is accomplished through the optoisolator U13 and associated components R51, R52, D21, R66 and
R67. R51 and R52 limit the current through the LED when the triac is on or off. With the triac off and a heater wire
connected then the optoisolator will remain off. Otherwise if a heater wire is not connected then the optoisolator will be
turned on and off in synchronisation with the secondary cycle. The output of the optoisolator feeds U4 on the control
board. This signal, with processor interpretation, provides the information to determine if the Heater Wire is connected
or open circuit and also the integrity of fuse F2, the 4 A fuse supplying power to the Heater Wire.
Q11 controls power to the heaterplate and is under control of optoisolator U12 and transistor Q12 via an output port
(HPC) on U4 on the control board. Resistors R64, R57 limit the gate current to the triac and with C33 form a snubber for
the triac and the optoisolator.
Transistors Q5 and Q6 are an RS232 level driver for the serial data interface.
4.4 PROBE TEMPERATURE VERSUS THERMISTOR RESISTANCE
TEMP (± 0.2 °C) RESISTANCE (Ω) TEMP (± 0.2 °C) RESISTANCE (Ω)
0 7352.8 36 1411.3
9 4702.2 37 1355.0
28 1976.6 38 1301.0
29 1893.3 39 1249.2
30 1814.4 40 1199.6
31 1739.2 41 1152.3
32 1667.2 42 1107.3
33 1598.2 43 1064.5
34 1532.9 44 1023.1
35 1470.6 60 560.3