STEPRACE: Service & Maintenance Manual - rev. 1.2
Page 6.16
Are the signals output by the
serial port on the CPU board
correct?
Replace the CPU board
Replace cable ST-1
NO
YES
6
A
Follow the step by step procedure to correctly diagnose the problem. Take particular care with the
checks highlighted by circled numbers, which are described in detail below:
Disconnect any race cables linking the machines before performing these checks.
The machine is configured as MASTER if it is assigned No. 1, and as SLAVE if it is
assigned any other number.
(1) Place the tester probes between pins 10 and 3 of connector CN1 on the CPU board, and check
that the reading is 5 Vdc when the machine is configured as MASTER, and 0 Vdc when the
machine is configured as SLAVE.
(2) Place the tester probes between pins 10 and 3 of connector CN1 on the alternator interface
board and check that the reading is 5 Vdc when the machine is configured as master, and 0
Vdc when the machine is configured as SLAVE.
(3) After changing the state of the Master – Slave signal, when the machine is turned back on
check that the relay switches by listening for its typical “clicking” sound.
(4) Place the tester probes between the pins of connector CN4 on the alternator interface board
and check that the measured voltages are those given in the table below:
Alternator interface
board
Voltage
(Vdc)
Signal CN1
CPU board
CN1 CN4 Master Slave
A – bus 14-3 14-3 3-7 3.7 3.7
B – bus 15-3 15-3 4-7 0.8 0.8
Y – bus 11-3 11-3 1-7 3.7 3.7
Z – bus 12-3 12-3 2-7 0.8 0.8
Table 6.7-1
(5) Check the cable by following the diagram in paragraph 2.5. “Wiring diagram”.
(6) Place the tester probes between the pins of connector CN1 on the CPU board and check that
the measured voltages are the same as those given in Table 6.7-1.
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