是否为使用不当引起的故障，如属于这类故障，则根据使用情况可初步判断出故障类型、发生部位。常见的使用不当包括供电电源故障、端子接线故障、模板安装故障、现场操作故障等。
如果不是使用故障，则可能是偶然性故障或系统运行时间较长所引发的故障。对于这类故障可按PLC的故障分布，依次检查、判断故障。首先检查与实际过程相连的传感器、检测开关、执行机构和负载是否有故障：然后检查PLC的I/O模板是否有故障：最后检查PLC的CPU是否有故障。
在检查PLC本身故障时，可参考PLC的CPU模板和电源模板上的指示灯。
采取上述步骤还检查不出故障部位和原因，则可能是系统设计错误，此时要重新检查系统设计，包括硬件设计和软件设计。
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PRECISION DIGITAL PD141AFO-3 VIGILANTE ANNUNCIATOR
(A6) 1 Sick Optic LCUAMNCRS Power Supply
Square D EDB24240 480Y / 277V, Thermal Magnetic Circuit Breaker, in Box
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Accuray Circuit Board #26437
Microscan 1950 mAh Replacement Battery, For MS-911 Scanner, !
Industrial Devices Controller S6961NP Scratch & Dent #55586
Westinghouse 60 HP Electric Motor HSB-60 #6087
LOT OF 2 CROUSE-HINDS DS181 COVER
Fischer Custom Communications FCCCDN, Passive Impedance Adapter Kit
(O2-1) 1 TEST PRODUCTS TL CONNECTOR
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Atc 331B-357-Q10Xx Timer (K2-3)
Schrader Bellows Cylinder FAS110421 #27292
Pacific Scientific S21-HNNA-HGNS-02 Brushless Servo Motor, !
Armstrong Tools X-110 1" Drive, 9" Length, Chrome Plated, Drive Extension
Vectron 80.000 MHz, Precision Crystal Oscillator
Allen Bradley Contact Kit Z-34042 #31897
Yaskawa Servopack SGDB-1EADGY48 #59926
(N1-1) BUSSMANN LPS-RK-400SP FUSE
Kistler 5039A222, Range 1# 20,000 pc, #2 25,000 pc Industrial Charge Amplifier
Hendry 0B2-20R, 10 Circuit Breaker, 20A Each, A/B Alarms, Fuse Panel Switch Unit
Namco Proximity Switch Ee Rsense (3402)
General Radio (GR) 874-K, DC to 4 GHz, 4700 pF, GR 874 to 874 Coupling Capacitor
(0310) Reliance PC Board Relay Card
Allen Bradley Keyboard 1770-FE Ser A #28850
Bulova PCOXO-HP01, HP .000 MHz, +20/30 VDC Quartz Crystal Oscillator
MICROSWITCH 5ML1-E1 LIMIT SWITCH
SCIENTIFIC TECHNOLOGIES INCORPORATED PC BOARD OSCILLATOR
(2994)E Allen Bradley 1775-L2 Processor Level 2 PLC 3
Wandel & Goltermann TK-12/TKN-12, 200 Hz to 18.6 MHz, Test Probe / Power Supply
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Square D EDB24240 480Y / 277V, Thermal Magnetic Circuit Breaker, in Box
(N1-1) 1 DATALOGIC CM1000 COMMUNICATIONS MODULE
(B1) 1 NIB MILLER FLUID POWER 051-KR BOLTED STAR BUSHING KIT
