Omron WDT Troubleshooting Help

[Guest Grac Mascarenhas]

Hi Ev1 I'm presently working on one of the old PlC by Omron "SYSMAC CV–series CV500/CV1000 CVM1 CPU21". Now my main problem is the WDT ( Watch Dog Timer ) Error., Due to which the entire systems goes into a reset condition & I'm unable to debug or in other words view any of the signals. So I wanted to know what are the different conditions that causes this WDT error to go High. And I also want to know if any timing violations cause this error if so what is the best way to come out of this condition & if anyone has worked on this board , can they please give me the list of signals that are effecting the WDT. There is a processor 80C186 being shared by TF250LF & TF 142NF, Can anyone give me the detailed operation happening between them. I'm very greatful for ur consideration. Thanking You, Grac Mascarenhas

[Jay Anthony 118]

Guest_Grac Mascarenhas: Please register at MrPLC.com and join the MRPLC.com community Register at MrPLC.com Please post more significant troubleshooting data about the CV CPU: 1. Is the CPU mounted to a rack? 2. What other modules are present on the rack? 3. What CPU indicators are lit? 4. What are the positions of the CPU dip switch? 5. Did this CPU ever work properly? 6. Is there an expansion memory card mounted to the CPU? 7. Is there a PCMCIA card mounted to the CPU? 8. What is the condition of the CPU battery? 9 Anything else related to hardware that you can tell us? It is my profound opininon that one of the above answers will lead us to the solution. I do not think it would be wise to start troubleshooting the CPU main board before checking out these items.

[Guest Grac]

Hi Jay, Thank you very much for your prompt reply. Here's the information 1.Yes the CPU is mounted on a rack(On CV500-BC101) 2.The Other modules present are a Digital Output module- OUT OD412 3.Only the Power & WDT , sometimes even this occurs ( WDT along with ALARM & ERROR LEDs Glow, but only for some time ,No idea why this happens ) 4.only the S/W 4 is in the DOWN position 5.YES 6.NO 7.NO 8.CPU battery is OK 9.More about hardware:This is what I can give information about: There are two chips (mainly )as I had told you earlier TF250LF & TF 142NF and there is a processor 80C186 being shared by these, & there are some memory chips.There is a sequencing of operations done by the processor & the 2 chips try to get access according to some rule . Now I doubt there might be some timing violations while the two are trying to access the data from memory or some other data. I need more information regarding the generation of the WDT, which is the module generating this and what the conditions are? Hope the information is sufficient. Can you also suggest me some study materials regarding these which would be a great help. Again thank you very much for your consideration.

[Jay Anthony 118]

I recommend disconnecting the battery from the CPU for at least 72 hours and see if it is a bad program. Else you will need to return it to Omron for repair.