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1756-L55/A Controller

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Respected Friends,

Good day. I face a serious issue please help me to fix the problem. 

We have a 1756-L55/A controller with 1756/M13 A memory card. after 2 or 3 months the program washout and the LED status on the controller are following


2. I/O--- OFF

3. RS232 --- SOILD RED


5. BAT-- OFF


At that time CONTROL NET MODULES OK Light for Chanel A and Chanel B are also blinking and communication not established via control net and serial port AB-DF1.

I switched off the power supply and after 10 second again power up the controller then OK LED becomes solid green. 

i download the program and its run fine.

But the problem is still there. In the controller properties the major fault shows 



what are the possible reason for wash out the program from the memory? 

At that time version 16.03 firmware installed and the rslogix program convert from version 10 to version 16.03. 

Is 1756 L555/A with 1756/M13 A support the version 10 firmware? i ask because the original program is in version 10 if its supported then i update the firm ware and download the original program.


Hope you will help me in this issue.


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I'm 99% sure the -L55 supports back to v10. I know that v16 is the newest it supports. We have about a dozen of these in service right now.

Here is what your CPU LEDs mean:

Run = solid green: PLC is in run mode

I/O = off: Either no I/O is configured or there is no program in the PLC

RS232 = solid red: ????, manual just says off or solid green

OK = solid red: non-recoverable fault, CPU has cleared the program

BAT = Off: battery is ok

Force = Off: no tags contain I/O force values and I/O forces are inactive


Here is an older version of the ControlLogix user manual that covers the -L55:


There is a KnowledgeBase article (278692) on this but it requires TechConnect access and really isn't that helpful for figuring out what happened, just how to recover, which you've already done. there's another manual here:

It says that if it persists, to contact Rockwell support. If you don't have a support contract, I would reach out to your local distributor for assistance. Ours has always been very helpful.

I remember having something weird happen once, but I can't find my notes from that far back (2011). It turned out to be the memory module. This processor has been out of production for a very long time, but you can probably find the CPU and/or memory module on the secondary market if you want to try a straight replacement instead of an upgrade.




Edited by Joe E.
Moved attachment in-line

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