T150/150G/T400/400G Course Computers
28
Type 150/150G/400/400G Course Computers Service Manual 83156-1
Type 150/400 Course Computers
Another switching regulator IC6, provides the main 5 Volt requirement, 5V-REG. A
filtered version of this, 5V-DIG supplies all the 5 Volt digital circuitry on the PCB. 5V-
DIG is further regulated down by linear regulator IC16. This generates the 3.3 Volt rail
(3VDD) required by the microcontroller IC15.
Drive Output
The main motor drive circuit consists of the H-Bridge formed by the FETs TR18, TR24,
TR34 and TR27. These four power devices control the current delivered to any drive unit
connected to terminals MOTOR1 and MOTOR2. Each FET is controlled by buffer circuits
which switch the gate terminals between ground and the appropriate drive potential (VREG
for TR24 and TR27 and VIN+12V for TR18 and TR34).
The buffer circuits are themselves controlled from four logic signals (HIGH-LEFT, LOW-
LEFT, LOW-RIGHT and HIGH-RIGHT), which emanate from logic chips IC11 and IC8 in
response to signals from the micro controller (PORT-D, STBD-D and PWM).
Comparator circuits IC5a and IC5b monitor the current flowing through the H-Bridge and
shut down the drive in the event of an over-current situation.
The H-Bridge can also be shut down in response to the WATCHDOG, RESET or KILL
signals going low. The buffers in IC24 and transistors TR80, TR49 and TR50 control this.
The H-Bridge provides direction and speed control of the motor. Speed control is achieved
by modulating the drive voltage at 20KHz for various duty cycle settings.
Spool Valve Control
Both the Type 150 and 400 Course Computers have dedicated ground connections for use
with solenoid valve drives. These connections provide a current limited ground return by
monitoring the current flow in sense resistor R133. When this current exceeds 2 Amps,
comparator IC10a changes state and shuts down the drive provided by H-Bridge high side
FETs TR18 and TR34.
Clutch Drive
The clutch output (TB11) is controlled by FET, TR56. The output voltage is normally a
nominal 12 Volts but can be connected direct to the incoming power rail by moving the
position of output fuse FS3. In the case of a 24 Volt power supply, this enables you to drive
a 24 Volt clutch if required.
In a similar manner to the Spool Valve drive, the clutch output current is sensed across
resistor R167 and compared against a fixed threshold by comparator IC10c. The
comparator output shuts down TR56 if the clutch current exceeds 4 Amps.
Fluxgate Compass
The compass is driven at 8 KHz by the buffer circuit consisting of TR36 and TR37. The
drive signal originates from the micro controller and the current amplified output is a.c.
coupled via capacitor C53 to the fluxgate drive (Blue) terminal.
