Allen Bradley MicroLogix 1500

This section describes how to troubleshoot your MicroLogix 1500 controller. This section will cover the process of understanding your controller LED status, a controller error recovery schematic, and identifying controller faults. 

Understanding MicroLogix 1500 Controller LEDs

The controller status LEDs provide a way to determine the current status of the controller if a programming device is not present, available, or connected. 

LED	Color	Indicates
POWER	Off	No input power
	Green	Power on
RUN	Off	MicroLogix 1500 controller is not in Run mode or REM Run
	Green	Controller is in Run mode or REM Run
	Green Flashing	System is not in Run mode. Memory module transfer is in process.
FAULT	Off	No fault detected
	Red Flashing	Faulted user program
	Red	Processor hardware fault or critical fault
FORCE	Off	No forces installed
	Amber	Forces installed
BATTERY LOW	Off	Battery OK
	Red	Battery needs replacement
COMM 0	Off	Flashes when communications are active
	Green
COMM 1 (1764-LRP only)	Off	Flashes when communications are active
	Green
DCOMM***	Off	User configured communications mode is active
	Green	Default communications mode active
INPUTS	Off	Input is not energized
	Green	Input is energized (logic status)
OUTPUTS	Off	Output is not energized
	Amber	Output is energized.

***When using a 1764-LRP processor, the DCOMM LED applies only to Channel 0. 

When Operating Normally

The POWER and RUN LEDs are on. If a force condition is present, the FORCE LED turns on and remains on until all forces are removed. 

When An Error Exists

If the LEDs Indicate	The Following Error Exists	Probable Cause	Recommended Action To Solve
All LEDs off	No input power or power supply error	No line power	Verify proper line voltage and connections to the controller.
		Power supply overload	This problem may occur intermittently if the power supply is overloaded when output loading and temperature varies.
Power and FAULT LEDs on solid	Hardware faulted	Processor Hardware Error	Cycle power.
		Loose wiring	Inspect connections to controller to ensure that they are connected.
Power LED on and FAULT LED flashing	Application fault	Hardware/Software Major Fault Detected	1. Monitor Status File Word S:6 for major error code. 2. Remove hardware/software condition causing fault.  3. Clear Major Error Halted flag, bit S2:1/13 Attempt a MicroLogix 1500 controller Run mode entry. If unsuccessful, repeat recommended action steps above.

Controller Error Recovery Schematic

Use the error recovery schematic below to help you diagnose software and hardware problems in the micro controller. The model provides common questions you might ask to help troubleshoot your system. Refer to the recommended pages within the model for further help. 

1. Is the error hardware related?
   1. If NO: (1) Identify the error code and description, (2) Refer to "When An Error Occurs" table (above) for probable cause and recommended action, (3) Clear the Fault, (4) Correct the condition causing the fault, (5) Return controller to RUN or any of the REM test modes, and (F) Test and verify system operation. 
   2. If YES: Are the wire connections tight?
      1. If NO: (1) Tighten wire connections, and (F). 
      2. If YES: Is the Power LED on? 
         1. If NO: Is power supplied to the controller?
            1. If YES: Refer to "When An Error Occurs" table (above) for probable cause and recommended action. 
            2. If NO: (1) Check power, and (F). 
         2. If YES: Is the RUN LED on?
            1. If YES: (F). 
            2. If NO: Is the Fault LED on?
               1. If YES: Refer to "When An Error Occurs" table (above) for probable cause and recommended action. 
               2. If NO: Is an input LED accurately showing status? 
                  1. If Yes: (F). 
                  2. If NO: Refer to "When An Error Occurs" table (above) for probable cause and recommended action. 

Identifying Controller Faults

While a program is executing, a fault may occur within the operating system or your program. When a fault occurs, you have several options to determine what the fault is and how to correct it. 

Automatically Clearing Faults

You can automatically clear a fault by cycling power to the MicroLogix 1500 controller when the Fault Override at Power-up bit (S:1/8) is set in the status file. You can also configure the controller to clear faults and go to RUN every time the controller is power cycled. This is a feature that OEMs can build into their equipment to allow end users to reset the controller. If the controller faults it can be reset by simply cycling power to the machine. To accomplish this, set the following bits in the status file: 

• S2:1/8 - Fault Override at Power-Up
• S2:1/12 - Mode Behavior

If the fault condition still occurs after cycling power, the controller reenters the fault mode. 

Manually Clearing Faults Using the Fault Routine

The occurrence of recoverable or non-recoverable user faults can cause the user fault subroutine to be executed. If the fault is recoverable, the subroutine can be used to correct the problem and clear the fault bit S:1/13. The controller then continues in the Run or test mode. The subroutine does not execute for non-user faults. Refer to the MicroLogix 1200 and MicroLogix 1500 Instruction Set Reference Manual publication 1762-RM001 for information on creating a user fault subroutine. 

MicroLogix 1500 Controller Repairs

Here at DO Supply, we offer repair services for your Allen-Bradley products, such as the Allen-Bradley MicroLogix 1500 Controller. Please select the Repairs tab for more information or to request a quote.