Siemens LOGO! 0BA8 Drops to STOP V1.08.x Firmware Troubleshooting

1. Problem Description

Field installations of the Siemens LOGO! 8 (order code suffix 0BA8) logic module have been reported to leave RUN mode and enter STOP mode without operator intervention. In water-well automation deployments across multiple sites, two LOGO! 0BA8 base units on firmware V1.08.01 and V1.08.02 switched out of RUN spontaneously. The unit was no longer executing the user program, the display showed STOP, and remote telemetry indicated the well controls were no longer responding. On arrival the technician recovered the controller by entering the ADMIN menu and selecting START.

The transition appears correlated with a mains supply event but is not conclusively proven in every report. Because the operator is only dispatched after the customer notices a loss of function, the controller is typically already in STOP, no diagnostic buffer is preserved in a way that is visible from the front panel, and the exact triggering condition must be reconstructed indirectly.

2. Affected Hardware and Firmware Matrix

The reported condition clusters around the LOGO! 8 generation base units with an integrated display. The 0BA8 generation was the first to use the naming convention order-code-suffix 0BA8, with the display-bearing variants carrying the suffix ...RCE or ...RCEo. The following matrix summarises what is reported in field service:

The defining pattern is the presence of the built-in display combined with a mid-range 1.08.x firmware. Units delivered without a display (...E variants such as 6ED1052-1FB08-0BA1) are not reported to exhibit the fault, even when the firmware version is identical.

3. LOGO! 0BA8 Production State (FSxx) Identification

Siemens uses an internal Production State (FS = Fertigungsstand) code stamped on the type label of each LOGO!. The FS code identifies the manufacturing revision, hardware revision, and firmware baseline bundled at the factory. Knowing the FS code is essential for support requests and for verifying whether a particular bug fix is already included.

To read the production state:

1. Power down the LOGO! and remove it from the DIN rail if the type label is on the rear face.
2. Locate the side label with the Siemens address block.
3. Read the FS: field. Examples: FS01, FS02, FS03.
4. Cross-reference the FS code against the firmware version reported in LOGO! → Diagnostics → Firmware on the device menu.

4. LOGO! Auto-Restart Behavior on Power Recovery

The intended behavior of the LOGO! 8 generation after a power failure is documented as follows:

• If the controller was in RUN when supply was lost, it returns to RUN automatically once supply is restored.
• If the controller was in STOP when supply was lost, it remains in STOP after restoration.
• Whether the unit attempts a RUN re-entry is independent of the user program content.

The factory default therefore makes a spontaneous drop to STOP a deviation from the documented power-on behavior. Any field occurrence of "controller is in STOP when mains returned" is by definition either:

1. A bug in firmware that mishandles the brown-out / power-good edge.
2. A user program setting that disables auto-restart (e.g., a flag-conditioned STOP rung).
3. A hardware fault on the base unit (memory corruption, supercap discharge).
4. An undocumented behavior introduced by a specific firmware / production state combination.

5. Root Cause Analysis: Why RUN-to-STOP Transitions Occur

For the symptom described — display-equipped 0BA8 units dropping to STOP, occasionally associated with power events, with non-networked units also affected — the candidate root causes are:

The most diagnostic single piece of information is the internal diagnostic buffer, which can only be read via LOGO! Soft Comfort in online mode. If the field technician does not have a PC on site, the next visit should be planned specifically to capture this buffer.

6. Diagnostic Procedure: Capturing the Event

Use the following procedure when arriving on site with a laptop running LOGO! Soft Comfort V8.x:

1. Connect the laptop to the LOGO! 230RCE via the Ethernet port on the left side of the base unit.
2. Set the laptop to a static IP in the same subnet (e.g., 192.168.0.10 / 255.255.255.0).
3. In LOGO! Soft Comfort, open the project for this site (or use Tools → Transfer → Read from LOGO! to upload the program currently on the unit).
4. Select Tools → Diagnostics → Online Diagnostics (or the equivalent menu item depending on Soft Comfort version).
5. Note the current firmware version, FS code, IP address, and mode (RUN / STOP).
6. Export the diagnostic buffer and the event log using File → Export → Diagnostic Buffer. Save the file with a timestamp.
7. If the LOGO! is currently in STOP, capture the cause field if displayed (e.g., STOP due to user request vs STOP due to power fail vs blank).
8. Force a power cycle on a controlled bench supply if practical, and observe whether the unit returns to RUN on its own.

7. Recovery: Returning the LOGO! to RUN via the HMI

If a laptop is unavailable, the standard recovery on a display-equipped LOGO! 8 is:

1. From the main screen, press ESC repeatedly until the status display appears.
2. Press the down arrow to navigate to the password / mode menu.
3. Enter the administrator password if one is set (factory default empty for older units, a value set during commissioning for newer ones).
4. Select START from the run/stop control.
5. Confirm the controller is back in RUN by observing the RUN indicator in the top-right of the display and verifying that outputs are scanning.

This restores service but does not address the root cause. The next occurrence is likely without further intervention.

8. Mitigations and Workarounds

Field-proven mitigations, in order of least to most invasive:

Adding a backup power supply alone is not a permanent solution if the underlying bug is firmware-driven: a controller that incorrectly interprets a normal power restoration as a STOP command will still drop out, even with a UPS sized to ride through the event.

9. Firmware Update Procedure

Siemens distributes LOGO! 8 firmware updates as BIN files loaded onto a standard SD card. The procedure:

1. Download the latest LOGO! 8 firmware package from the Siemens Industry Online Support portal.
2. Extract the BIN file and place it in the root directory of a FAT32-formatted SD card (capacity up to 32 GB supported by most LOGO! 8 firmware revisions).
3. Insert the SD card into the LOGO! while power is OFF.
4. Apply power. The LOGO! detects the firmware file and prompts UPDATE FIRMWARE? on the display.
5. Confirm with YES. The update takes approximately 60 to 120 seconds. Do not interrupt power during the update.
6. After reboot, verify the new firmware version under LOGO! → Diagnostics → Firmware.
7. Re-transfer the user program from LOGO! Soft Comfort to ensure compiled code matches the new firmware baseline.

10. Siemens Support Request Submission

If the fault recurs after the mitigations above, open a formal support request via the Siemens Industry Online Support portal. The submission must include:

• Article number (full 6ED1... reference on the type label).
• FS (production state) code.
• Firmware version as displayed on the unit.
• Order code / serial number.
• Diagnostic buffer export from LOGO! Soft Comfort.
• Description of the power supply environment (nominal voltage, observed disturbances, presence of UPS, presence of large motors on the same feeder).
• Frequency of recurrence and any correlation with weather or load events.
• Recovery steps performed each time.

For North American deployments, Siemens Industry Inc. provides telephone support for the LOGO! product line via the regional technical support hotline. Provide the data above at first contact; expect an initial triage within one business day.

11. Verification After Recovery

After applying any mitigation, verify by:

1. Confirming the unit returns to RUN on its own after a controlled power-down / power-up cycle. Do this five consecutive times.
2. Capturing the diagnostic buffer online and confirming the cause-of-STOP field is empty on each cycle.
3. Leaving the unit under observation for at least one full normal operating cycle (one well pump cycle, typically 24 hours for residential wells).
4. Documenting the firmware version, FS code, and program checksum in the site log so that any future event can be compared.

12. Long-Term Recommendation for Multi-Site Fleets

For organisations running tens to hundreds of LOGO! 8 controllers in the same role (e.g., 30 water-well sites), the recommended practice is:

• Standardise all units to a single firmware baseline.
• Maintain a small bench-test fleet of the same FS code for reproducing field reports.
• Capture diagnostic buffers from every site visit and aggregate them — a pattern that looks isolated on a single unit often resolves into a clear firmware revision problem when 30 reports are combined.
• Use LOGO! Soft Comfort's Project → Properties to embed the firmware target and FS code into the project file so that the deployed binary always carries its compatibility metadata.

This avoids the failure mode where a controller that worked for years suddenly starts exhibiting a firmware bug after a Soft Comfort update that targets a newer firmware baseline by default.