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Troubleshooting Tutorial: Common SLC 500 Faults – Part 3: I/O Faults

Programmable Logic Controllers (PLC) such as Allen-Bradley’s SLC 500 Modular or Fixed style hardware are designed with capability of self-diagnostics. With Self-diagnostics, the controller is able to detect the operational status of every member module and report this externally through varying behavior of built-in LED indicators and internally via the diagnostic buffer. This is part 3 of our tutorial for troubleshooting common SLC 500 Faults.
In this section, we will discuss common SLC 500 I/O Faults.

Before proceeding, it is important to understandthe structure of the error code. I/O errors reported by the CPU is provided with slot number.    
So for an error code xx50, a chassis data error, the code represents:

                                xx as slot number in Hexadecimal (see table below);
50 as the fixed error code provided by the controller.

Chassis data error is detected

Hardware Fault TypeI/O Errors
Error Code xx50
Error DescriptionA chassis data error is detected.
CauseDefective chassis caused by electrical noise, power surge, intermittent power supply and improper grounding.
Resolution(a) Download program and run.
(b) Verify grounding integrity, install surge and noise suppression devices.
(c) Replace chassis
Detailed Stepsa) To download program and Run, refer to the appendix
To Verify grounding integrity, install surge and noise suppression devices;
a. Perform physical hardware check, retightening of grounding screws and conduct ground cable continuity.
b. If surge and noise protection are installed, verify functionality of each devices otherwise, replace or install.
c. Relocate and reinstall the chassis to a different panel or enclosure.

To replace chassis;
a. ensure that that the replacement unit is of the same part number otherwise, hardware reconfiguration is needed and downloading of the entire program is required.

Undetected or missing module

Hardware Fault TypeI/O Errors
Error Codexx52
Error DescriptionA module required for the user program is detected as missing or removed.
CauseMissing or removed I/O module; Damaged module
Resolution(a) Replace or Install the appropriate module
(b) Disable the slot in the status file S:11 and S:12
Detailed StepsTo install or replace module;
a. Disconnect power
b. Align module with the chassis slot.
c. Slide the module into place and push gently until the locking tab is in place.
d. Apply power to the rack.

To disable the slot within Status file S:11 and S:12;
a. Identify the specific slot as pointed by the error code.
b. Open the Data File status and navigate through the I/O tab.

c. Disable the specific slot by changing value from 1 to 0. In this example, slot 8 is disabled. You can disable other  slots, similarly.

Hardware Interrupt problem

Hardware Fault TypeI/O Errors
Error Codexx5A
Error DescriptionHardware interrupt problem
CauseIf this is a discrete I/O module, this is a noise problem. If this is a specialty I/O module, refer to the user manual for the module.
ResolutionResolution depends on the type of the specialty module installed. The specific user manual must be used to refer to the appropriate resolution.

Module inserted under power

Hardware Fault TypeI/O Errors
Error Codexx94
Error DescriptionA module has been detected as being inserted under power in the run or test mode. This can also mean that an I/O module has reset itself.
CauseModule was installed to the chassis under power; The module performed self-reset.
Resolution(a) Remove the module, clear fault and change controller mode to RUN.
(b) Reconfigure hardware definition and include the installed module. Download the user program
Detailed StepsTo remove the module, clear fault and change controller mode to RUN;
a. Disconnect power
b. Remove the module by pressing and holding the module release located on each self-locking tab and slide the module out of the chassis slot.
c. Once the module is removed, go online with the controller and clear fault.
d. Once fault is cleared, change controller to RUN mode.

To reconfigure hardware definition;
a. Revise the user program offline using the RSLogix 500 programming software.
b. Open the hardware configuration and update hardware definition. Double Click I/O configuration (1) to open the hardware selection window. Select the equivalent module (2) from the hardware catalog. Once the equivalent module is selected, perform (3) Drag and Drop operation to insert the module to the actual I/O configuration.
c. Once hardware is appropriately configured, compile and download the program.

Battery Low

Hardware Fault TypeStatus
Status CodeS:5/11 Battery low bit set to 1
Status DescriptionThis bit is set whenever the Battery Low LED is on. The bit is cleared when the Battery Low LED is off..
CauseLow battery charge
ResolutionBattery Replacement
Detailed StepsIt is important to recognize that Battery Low indication is a Status indication only and not a Fault. However, many treats this status indication as “fault” in some sense as a completely discharged battery may lead to a variety of fatal errors specifically, program related errors. To address low battery indication, battery replacement is required.

To replace battery of an SLC 5/01 -5/02 processor;

a. Without removing the power supplied to the processor, open the processor swing door and locate the battery.
b. Unplug existing battery connector and remove from the retainer clips.
c. Insert the replacement battery by allowing it to be held by the same retainer clips.
d. Engage the battery connector.
e. Close the processor swing door.

To replace battery of an SLC 5/03 -5/04 and -5/05 processor;
a. Remove power supply.
b. Uninstall the processor module.
c. The battery can be seen near the bottom of the Processor circuit board.
d. Remove the old battery.
e. Install the new battery to the same location where the old battery is removed.
f. Re-insert processor module to the chassis.
g. Power-up the SLC 500 chassis.

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This entry was posted on April 9th, 2021 and is filed under Uncategorized. Both comments and pings are currently closed.

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