# PLC Panel troubleshooting

**URL:** <https://forumautomation.com/t/plc-panel-troubleshooting/4137>\
**Category:** PLC (Programmable Logic Controllers)\
**Created:** [July 17, 2018, 2:34pm UTC](https://forumautomation.com/t/plc-panel-troubleshooting/4137 "2018-07-17T14:34:12Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![sivaranjith](https://forumautomation.com/letter_avatar_proxy/v4/letter/s/ba9def/32.png) [@sivaranjith](https://forumautomation.com/u/sivaranjith)\
**Post date:** [July 17, 2018, 2:34pm UTC](https://forumautomation.com/t/plc-panel-troubleshooting/4137/1 "2018-07-17T14:34:12Z")

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[**PLC**](https://forumautomation.com/c/plc-programmable-logic-controllers) troubleshooting is to correct the common operating problems with system components.

### Check for adequate power:

An under-powered unit could result in unpredictable behavior.

- The 400/600 DC powered terminals require 24V dc at 1.0 A.

- The 400/600 AC powered terminals require 85 to 264V ac.

- The 700-1500 DC powered terminals require 24V dc at 2.9 A.

- The AC Power Supply (2711P-RSACDIN) for 700-1500 terminals meets Class 2/SELV requirements.

### Check LED indicators on the terminal at startup:

The terminals have two [**LED**](https://en.wikipedia.org/wiki/Light-emitting_diode) indicators to isolate operating problems:

- COMM indicator (green) for communications
- FAULT indicator (red) for hardware faults

The red LED should be Off, except for a few brief flashes, and the green LED should be On.

- If the LEDs remain Off on the 700-1500 terminals, the power supply or logic module has failed. Check the power cable. Replace the logic module if the power is within range; if not, replace the power supply.

- If the LEDs remain off on the 400/600 terminals, check the power cable.

### Check the voltages and temperatures:

Display Temperatures should be less than 55 °C. The CPU temperature should be less than 95 °C.

If the temperatures are higher, check for obstructed airflow through the chassis and attempt to moderate the ambient temperatures within the enclosure and surroundings.

### Ethernet Cable connection:

Check for good connections and things such as quality, crimping, hub connection, and uplink ports. A bad Ethernet connection and the absence of a valid IP address are typically reported in a Communications error message box. Do not allow devices on the network with same (host) name.

### Troubleshooting Input modules:

The main purpose of the I/O interface is to condition the various signals received from or sent to the external input and output devices.

 ![plcin](https://cdn.forumautomation.com/original/2X/f/fb65e25060ae9814cc9b3ab5c7791760da345d69.png)

An input filter eliminates false signals due to contact rebound or electrical interference; Optical isolation protects the circuits of the backplane by isolating the logic circuits from the input signals; The logic circuits process the signal; An input LED turns on or off to indicate the status of the corresponding input device.

### Troubleshooting Output modules:

Output modules converts signal from the processor to levels capable of driving the connected discrete or analog output devices.

 ![plcout](https://cdn.forumautomation.com/original/2X/d/dfb76a551b5a04d74b78807f10e4398c08207284.png)

The processor determines the output status; Logic circuits maintain the output status. An output LED indicates the status of the output signal, Optical isolation separates logic and backplane circuits from field signals; The output driver turns the corresponding output on or off.

DC outputs typically are used to drive high-current electromagnetic loads such as solenoids, relays, valves, and motor starters.

Analog outputs can be used to drive devices such as voltmeters, X-Y recorders, servomotor drives, and valves through the use of transducers.