The Issue
When using Control Expert 16.0 to transfer a program to a backup (standby) M580 controller, the backup PLC may enter a “No Conf” (No Configuration) state. When this happens, the standard transfer procedure does not complete — the backup controller does not accept the program.
What “No Conf” Means
The PLC is running but has no valid program configuration loaded. It cannot synchronize with the primary controller because it has nothing to synchronize to. The hot standby transfer mechanism expects both controllers to have a valid program base — with “No Conf,” that prerequisite is not met.
Resolution
- A site person must power cycle the backup PLC. This clears the “No Conf” state and puts the controller into a clean startup condition.
- After the power cycle, connect directly to the backup controller (not through the primary) using Control Expert.
- Download the program directly to the backup PLC. Do not rely on the hot standby synchronization to push the program over.
- Once the backup has a valid program, re-establish the hot standby link and verify synchronization status.
Why Remote Resolution Is Difficult
If you are troubleshooting remotely and do not have a network path directly to the backup controller, you are dependent on someone on site to physically power cycle the PLC and connect a programming cable. Plan for this — ensure site contacts know where the backup PLC is located and how to power cycle it safely.
Prevention
- Always download to both primary and backup controllers during initial commissioning — do not assume the hot standby sync will handle it.
- After any program modification, verify the backup controller has the updated program. Check the program revision/checksum on both controllers.