
8. TROUBLESHOOTING
B–62755EN/01
378
920: Watch dog alarm or RAM parity in servo control module
has occurred in servo control module on the main CPU board
922: Above alarm has occurred in servo control module on the option 3
board
The timer used to monitor the operation of CPU is called the watch dog
timer. The CPU resets timer time every time a constant time has passed.
When an error occurs in CPU or peripheral device, timer is not reset but
the alarm is informed.
Refer to alarm 910 to 915
The servo module includes servo RAM, watch dog timer circuit, etc.
Defectiveness of hardware, abnormality or malfunctioning of detection
circuit or the like is considered. Therefore, replace servo module on the
main CPU board for alarm 920 and 921; replace servo module on the
option 2 board for alarm 922 and 923.
Servo module
Main
CPU
ROM
RAM
(A20B–2902–0061, A20B–2902–0070)
CPU or peripheral circuits may be faulty. Replace the main CPU board.
Software may not work properly due to failure of FROM module. Change
FROM module.
DC output voltage of power supply unit may be faulty. Replace the power
supply unit.
8.33
ALARM 920, 922
(WATCH DOG OR
RAM PARITY)
points
D Watch dog timer alarm
D RAM parity error
Causes and Remedies
D Servo control module is
faulty
D Main CPU board is faulty
D CNC control software
ROM module is faulty
D Power supply unit is
faulty