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Support > Easy PLC System Repairs

Troubleshooting Guide For Easy PLC System Repairs

  • Introduction

    Easy PLC System RepairsImage: Easy PLC Repairs

    Welcome to PDF Electric & Supply Company repair department. Our 33 years of automation expertise allows us to provide a process for identifying PLC problems as well as test procedures, which will help you recover from a factory-down situation.

    In this guide we are going to show you some of our techniques to identify PLC board failures so that you may fix them yourself.

  • Step 1 – Identify Your Module Type.

    Easy PLC System RepairsImage: Indentify Your Module Type

    When we repair PLC parts, we break them into three categories:

    • Intelligent Modules, consisting of CPUs and communication hardware;
    • Analog Modules, measuring current or voltage, including thermocouples and RTDs;
    • Discrete Modules, 24 volts AC or DC up to 230 volts AC.
  • Step 2 – Common Intelligent Module Faults:

    Easy PLC System Repairs
    Image: Battery Terminals
    Easy PLC System Repairs Image: On Board Pins

    Memory Fault

    The primary failure we see in PLC intelligent modules is a memory fault. The processor experiences a spike or glitch that hangs the processor memory. In many cases, simply removing the battery and shorting the two battery pins on the module will discharge the on-board capacitor and totally erase any RAM-based logic. This may clear the memory problem.

    ** Please Note ** You are erasing your program and you will have to reload it, so make sure you have a current backup copy.

    The manufacturers are so aware of this issue that many have discreetly installed small contact points hidden on the boards for their own field service engineers. This technique should save you an unneeded, expensive repair fee, as well as get your process machine back up in minutes.

    Communication Port Faults

    Other common failures in intelligent modules are focused around serial and Ethernet communication ports. Communication wires may create antennas and can destroy communication driver-integrated circuits. If there is a secondary communication port unused, simply move your communication cable to a working port and reconfigure your device.

  • Step 3 – Common Analog Module Faults:

    Easy PLC System Repairs
    Image: Communications Chip
    Easy PLC System RepairsImage: Comms Port

    Ground Error

    With analog modules, we consistently receive these modules in for repair and find out nothing wrong with them, only to learn that a ground error had occurred in the factory that made the analog card suspect. Ground loops, noise from a newly-installed AC drive, or a simple loose shield wire will create an erratic signal which gets misdiagnosed as a bad module. Move your analog signal wire to another PLC input point, you can see if it follows the wire, not the PLC point. This will allow you to determine if it is a field wiring problem or a PLC part problem.

  • Step 4 – Common Discrete Module Faults:

    Easy PLC System Repairs
    Image: Glass Tubes Fuses
    Easy PLC System RepairsImage: Ceramic PICO Fuse

    The most common module sent in for repairs are discrete modules from 24 volts to 230 volts. Luckily, these are also the easiest to repair and cost the least.

    Blown Fuses

    Fuses are the key to field repairing a digital I/O PLC card. In most cases, when a fuse blows in a digital PLC card it disables more than one output. If you see a group of 4, 8 or 16 points fail all at once, simply remove your module and test the internal fuses with an inexpensive Ohm meter.

    Fuses are no more than a couple dollars and can be found at any local electronics store.

    There are two basic types of fuses: the traditional glass fuse and the ceramic PICO fuse. Both can be replaced with an inexpensive soldering iron.

  • Step 5 - Additional Support and Repair Options

    Easy PLC System Repairs

    We hope that our troubleshooting guide has helped you track down the problem in your PLC system.

    If these techniques have not resolved your PLC problem, then PDF Electric & Supply is here to provide quality repairs. Our standard three-year PDF Supply warranty ensures years of reliable performance.

    If our quick turnaround is still not fast enough, we will ship you a replacement unit out today and issue core credit for most failed parts.

    PDF Supply: quality repairs, same-day shipments at a competitive price.

    Please contact us at 1-800-360-6802.

    We offer:

    • Repair
    • Repair with Exchange Credit
    • Remanufactured - 3 year PDF Supply warranty

PDF Supply sells used surplus products. PDF Supply is not an authorized distributor, affiliate, or representative for the brands we carry. Products sold by PDF Supply come with PDF Supply’s 1-year, 2-year, or 3-year warranty and do not come with the original manufacturer’s warranty. Designated trademarks, brand names and brands appearing herein are the property of their respective owners. This website is not sanctioned or approved by any manufacturer or tradename listed.

Rockwell Disclaimer: The product is used surplus. PDF Supply is not an authorized surplus dealer or affiliate for the Manufacturer of this product. The product may have older date codes or be an older series than that available direct from the factory or authorized dealers. Because PDF Supply is not an authorized distributor of this product, the Original Manufacturer’s warranty does not apply. While many Allen-Bradley PLC products will have firmware already installed, PDF Supply makes no representation as to whether a PLC product will or will not have firmware and, if it does have firmware, whether the firmware is the revision level that you need for your application. PDF Supply also makes no representations as to your ability or right to download or otherwise obtain firmware for the product from Rockwell, its distributors, or any other source. PDF Supply also makes no representations as to your right to install any such firmware on the product. PDF Supply will not obtain or supply firmware on your behalf. It is your obligation to comply with the terms of any End-User License Agreement or similar document related to obtaining or installing firmware.