Smiths Graseby 3200, Technical & Service Manual

Page: 49 / 117

Smiths Medical International Ltd.
3200 Service Manual Issue 5 (August 2004)
4 — 6
Input/output serial interface
The remaining five output lines on IC8 are used to activate transistors Q9 to Q13 inclusive,
and these transistors control the illumination of the syringe size indication LEDs, D17 to D21.
The outputs from IC9 are used to control which group of opto-sensors are activated and also
to activate transistors Q14, Q15, and Q16: these transistors control the illumination of the
ALARM , START and STOP LEDs. Resistors R52 to R57 inclusive are current limiters.
The display is a 20 character, two line Vacuum Fluorescent Display (VFD) that is linked to the
main board by PL5.
The display data is transmitted via MOSI to IC10, which is enabled by FPSEL2. The output of
IC10 is input to the VFD by a signal from VFDSTB, when the VFD_BUSY signal signifies to the
processor that the VFD is ready to accept the next byte of data.
The supervisor chip IC15 can turn on the sounder independently of the microprocessor via
ENABLE_MOTOR. This independence occurs if the processor malfunctions and is unable to
produce its own sounder control; in which case the supervisor chip’s watchdog would timeout
thus generating an ENABLE_MOTOR control.
D28 prevents a low signal from SOUND drawing a current from IC15. Q8 and associated
components C30, R39, R40 and R41 constitute a low-pass filter which allows the PWM signal
SOUND from the micro-controller to activate the sounder. The sounder is connected to PL2.
R3, R10, R76, C2 and Q2 enable the main processor to detect the presence or absence of
mains power. When mains power is present a low signal is applied to pin 14 of IC11.
This signal is then transmitted serially to the processor via MISO.
The pump utilizes a primary switching power supply (see Figure 4.11 ).
The advantages of this type of supply over a conventional secondary switching power supply
include the following:
• greater efficiency,
• larger power capability for a given size of supply, and
• a smaller transformer is needed for the equivalent power.
The regulator circuit is based on a universal input switch-mode controller, IC1 (see Figure 4.12 ).
IC1 uses a current mode, pulse width modulation control circuit, which allows it to operate
over a wide range of AC input voltages i.e. from at least 90 V to 270 V AC.
The regulator also provides a 7 V DC supply for the motor and the LEDs. This supply is then
used to provide a 5 V DC supply for the logic circuits
The regulator circuit is protected by a mains fuse, FS2. The mains supply is then filtered by
C14 and L2. R20 allows the residual charge on C14 to be dissipated when the pump is
removed from the mains supply.
The output from the bridge rectifier D7 is smoothed by C10 and transient current limited by
varistor V1. When V1 is cold, the resistance is high and current is limited. As the thermistor
warms up, the resistance decreases, allowing the current to increase. The output from VR1 is
used to start up IC1 via pin 1. It is also fed to the primary winding, pin 6 on the power
transformer.
Regulator
board