1756-dnb losing scanlist

I'm on an out of town startup. I have multiple cnet drops, some with 1756-dnb attached to Rockwell Intellecenter mccs. Twice during the startup plant wide power was lost for several hours. First time for a main transformer feed switchover to the plant, second time due to a tree falling on power lines during a wind storm. Out of the 6 1756-dnbs all but one had no issues with the power failure. This one dnb both times lost its scanlist requiring a reload using rsnetworx.

Does this sound like a pooched 1756-dnb?

I've commissioned many dozens of 1756-DNBs and have never seen one with a defective flash memory, but I suppose there's always a first time. I would be amazed if a defective flash memory didn't also result in a POST or self-diagnostic failure.

Check the connected controller's program to be sure they're not running a scanlist archive/restore routine, or sending a Reset command (CIP service 0x05) to the module.

Ken Roach said:

I've commissioned many dozens of 1756-DNBs and have never seen one with a defective flash memory, but I suppose there's always a first time. I would be amazed if a defective flash memory didn't also result in a POST or self-diagnostic failure.

Check the connected controller's program to be sure they're not running a scanlist archive/restore routine, or sending a Reset command (CIP service 0x05) to the module.

Click to expand...

Definitely not, i programmed the plc and am not smart enough to even do that.

While I agree that replacement is probably appropriate, I'm curious about what happened.

If these are 1756-DNB without the USB port and the rotary switches (Series A or B), did they also revert to Node 63 and 125 kb/s ?

I'm trying to figure out how the Scanlist Objects, which are stored in NVRAM like everything else, could get erased without otherwise damaging the module.

How did you determine that the scanlist was empty; did the 1756-DNB show an error code 75, or did you upload the scanlist and find no entries ?

Ken Roach said:

While I agree that replacement is probably appropriate, I'm curious about what happened.

If these are 1756-DNB without the USB port and the rotary switches (Series A or B), did they also revert to Node 63 and 125 kb/s ?

I'm trying to figure out how the Scanlist Objects, which are stored in NVRAM like everything else, could get erased without otherwise damaging the module.

How did you determine that the scanlist was empty; did the 1756-DNB show an error code 75, or did you upload the scanlist and find no entries ?

Click to expand...

Ken,

after both power outages, the cards appeared normal. Both times the status LEDs indicated it was in in Run mode and at Node 0. All motors associated with this card would be non functioning. Every so often the Mod/net LED would flash red ans "No Rx (or Tx)" would flash on the staus Leds.
Doing an upload from the scanner would reveal the Scanlist was gone. After doing a download to the scanner, the motors associated with this card were online.

Today I will probably swap out the 1756-DNB with a non commissioned Devicenet MCC to elimante a card problem.

The joys of working on out of town jobs on a weekend, getting parts.