S120 ErrorDetail 421

There are several topics on the forum on the issue of a 421 error with motion control.  However, none of them seem to solve the problem. 

I have an S7-1500TF CPU, specifically a 1517TF-3 PN/DP.  Using TIA Portal V15.

There are two S120 control units on ProfiNet.

There are 4 normal S120 drives, plus a 5th drive that runs 6 S120M drive motors.

Everything runs fine.  At some point, one of the S120M drives gives an error, with ErrorDetail 421.  The error clears easily and the drive re-enables.  Between 1 and 10 minutes later, I get the fault again, on the same drive. 

In the List of Technology alarms, 421 is described as "Faulty drive at the logical address"

However, in the detail section it says "Faulty encoder at the logical address."

In yet a third place, 421 is also called out in section 3.2.5.6, saying it results from the Basic Safety Function being triggered.

I don't think anything is going on with safety, since none of the other drives are affected.  I don't actually know how to check that, however, especially since I don't have the password for any of the safety function blocks.

To recap, I keep getting a 421 alarm on 1 of 10 servos.  What can I do?

Thanks,

James

Hi, 

as ChristophD says you have to go online with the drive to see the real drive fault.

 Fault 421 on the PLC side just says that the drive stopped by its own without being controlled by the TO. The real reason you can just get from the drive. I think your drive project must be a STARTER project as you use S120M. So open that project, go online with the drive and check the actual faults then. 

Thanks for the replies.  Going online with Starter did indeed give me a specific, meaningful error message. 

Regards,

James