Three different SLC5/03 same CRC error

Wondering if any of you old timers have seen a case where you can download to the processor no problem, but on power cycle: fault, and no program? Three separate processors, 2 are new. Fresh batts in all.

I checked my load bits for memory module everything is set low. I have no problem reloading any of the processors and they run fine until next power cycle.

I'm scratching my head on this one. I have changed out hundreds of processors no problem, well not usually.


P.S. Ron if your around just want to give you a shoutout. I sent several techs your way a few years back. Excellent training my man. I heard you were retiring back then, hope your doing good.

I can't remember the exact issue I got but I had an issue years ago with a SLC and getting it to load the program. Turned out to be the power supply. Swapped it out and no problems.

merchantg said:

Wondering if any of you old timers have seen a case where you can download to the processor no problem, but on power cycle: fault, and no program? Three separate processors, 2 are new. Fresh batts in all.

I checked my load bits for memory module everything is set low. I have no problem reloading any of the processors and they run fine until next power cycle.

I'm scratching my head on this one. I have changed out hundreds of processors no problem, well not usually.


P.S. Ron if your around just want to give you a shoutout. I sent several techs your way a few years back. Excellent training my man. I heard you were retiring back then, hope your doing good.

Click to expand...

Normally ... heh heh ... NORMAL failure .. heh heh

.. Normally .. I would suggest checking for a ground on the communications. Not a low impedance short to ground or shield ... something like 10 - 20 ohms? In my experience, the SLC do not like any loads on the communications during power up. The terminating resistors for RS485 are obviously fine. Less resistance to ground than the signal to signal resistors.

BUT - I've only seen that after a SLC has been hit repeatedly with the same condition on powerup. Just before it gives up totally and stops talking to almost everything. Since you have 3, and all of them do it ... I've not seen this particular issue.

Disconnecting comms on powerup is likely something you've already tried.

Multiple processors suggests it’s local to the rack. Power supply issues are common and can cause loss of program.

Another vote for the power supply.

And my friends it was indeed the power supply. Thank you for the replys. I have changed many a bad power supply but never caused this exact issue.

Hopefully this thread will help someone else.

merchantg said:

And my friends it was indeed the power supply. Thank you for the replys. I have changed many a bad power supply but never caused this exact issue.

Hopefully this thread will help someone else.

Click to expand...

Thanks for coming back and posting :site:

Not just SLC's.

I have had to replace 2 ControlLogix power supplies for one PLC repeatedly losing its program (even a new CPU) and another kept shutting down the Ethernet comm's.

Yes had the same problem a couple of times, Racks when they get older and PSU's, on two occasions had a fault in NVRam Checksum error, re-load the program would run for a few days, then crash, replaced processor, Then fitted an Eprom and new battery, turned out to be the PSU, same on another but turned out to be rack.