Allen Bradley SLC500 Fault

We have had a conveyor line that has been running for 10 years with no problems. This week it started shutting down and when I checked the Allen Bradley SLC500 PLC it had a fault each time it stopped running. The Fault that comes up is 0002h and the explanation it shows in the RSLogix software is as follows:

Unexpected hardware watchdog timeout or an ASIC reset occured

I havent seen this one before and not sure exactly what to do to make it go away permanently. The only way I have been able to get rid of the fault each time and get it back up and running was to download the program back into the CPU each time.

The system consists of the following:
Slot 0: 5/02 CPU with 4K EEPROM installed
Slot 1: 16 input 100/120VAC
Slot 2: 16 input 100/120VAC
Slot 3: 16 input 100/120VAC
Slot 4; 16 input 100/120VAC
Slot 5: 16 output (Triac)
Slot 6: 16 output (Triac)
Slot 7: 16 output (Triac)
Slot 8: empty
Slot 9: 1747-KE Interface Module

When the system was installed 10 years ago, there was a modem plugged into the interface module in slot 9 so the company that installed the system would troubleshoot the system from there location. The modem is still attached to the interface card but is no longer used.

If the program in the CPU is running the the power is turned on, I get the fault when the power is turned back on. I reload the program and I am able to put the CPU back in RUN they can are able to run the conveyor. The last two days, even though the power is left on overnight, I come in to the same fault. Once the program is reloaded, the conveyor line runs the rest of the day.

I have replaced the 5/02 CPU with our spare one and also changed the EEPROM and installed a new battery in the CPU. If anyone has any suggestions, I would greatly appreciate it.
Thanks
Fred Johns
Day Timer, Inc.

I've had a bad backplane do this too, its a PITA to troubleshoot because it could also be a module causing the issue.

The watchdog timeout means that the I/O scan took longer than expected, it is adjustable I believe. It's been awhile.

Hope this helps

Thanks for your help. My next move is going to be taking out all of the cards, set the CPU back to the default settings, install a configuration with just the cpu and power it up and see if I get the same fault

See picture below.

How do i use the autoload feature and have it load from the mem module. I have a mem module installed but right now it doesnt load from it

fredjohns said:

How do i use the autoload feature and have it load from the mem module. I have a mem module installed but right now it doesnt load from it

Click to expand...

See link to the manual below, page B-8. But that is a band-aid.

http://literature.rockwellautomation.com/idc/groups/literature/documents/rm/1747-rm001_-en-p.pdf

Yea, I want to use the autoload for after I figure out what the problem is with the PLC..Any suggestions for the best way to troubleshoot this problem

fredjohns said:

Yea, I want to use the autoload for after I figure out what the problem is with the PLC..Any suggestions for the best way to troubleshoot this problem

Click to expand...

From the diagram posted above, after 10 years I would check and double check grounding. Then the surge protection if any.
Then replace the rack power supply if you have another one.
Then remove output modules and replace one at a time if removing
corrected the problem. ( see status S:11,S:12 for module and slot enable control while doing this)

Thanks, I do have another power supply so when I get back to the plant tomorrow I will change the power supply after checking all the grounds and surgeprotection.
Fred