Troubleshooting Siemens LOGO! 8 No Power: 6ED1052-1CC08-0BA0 Fix

1. Problem Description

A Siemens LOGO! 8.2 base module, article number 6ED1052-1CC08-0BA0 running firmware V1.82.02, presents a complete "dead unit" symptom set:

• Integrated 6-line LCD is fully dark — no menu, no date/time, no cursor.
• No relay actuation on outputs Q1–Q4 even when inputs are forced.
• Ethernet RJ45 shows no link LEDs (no 100/10 Mb/s activity).
• LOGO! Soft Comfort, the LOGO! Web Server, and any Modbus TCP client fail to discover the device.
• External 24 V DC supply is verified present at the power terminals (fuse intact, polarity correct).

When a 24 V DC LOGO! shows this exact combination of symptoms with a confirmed supply, the base unit has suffered an internal hardware failure that field service cannot repair. The remainder of this article documents the diagnostic sequence to rule out the user-recoverable causes before invoking RMA, and the verification tests that confirm the base module — not an expansion, display, or external network — is the point of failure.

2. Affected Hardware Identification

Confirm the exact article number before troubleshooting — a different LOGO! 8 variant changes the supply topology, the input thresholds, and the output stage, all of which alter the diagnosis path.

The full technical specification, including EMC behavior, insulation coordination, and ambient limits, is published in the LOGO! 8.2 Manual (Siemens Support entry 109751635) and the LOGO! 8 Product Information Sheet.

3. Symptom Classification

Not every "the LOGO! does nothing" report is the same fault. Classify the symptom set before proceeding:

The source case matches row 3: dark display, no link LEDs, and a verified 24 V supply at the terminals. The sequence below eliminates the false positives from rows 1, 2, and 5 before concluding row 3.

4. Internal Power Architecture

Understanding the internal stages explains why a confirmed terminal voltage does not prove a healthy module.

1. Input protection block — a PTC resettable fuse (≈ 2.5 A hold) in series with a TVS / varistor clamp to absorb transient overvoltage. Reverse polarity is blocked by a Schottky diode in the return path. An accidental reverse connection forward-biases the diode and forces the full supply current through the PTC until it trips. If the diode or PTC is the only damaged component the base is non-recoverable without board-level repair.
2. Bulk capacitance — a 220–470 µF electrolytic that handles the inrush of the downstream converter. Aged electrolytics in a 5+ year old base can go high-ESR, causing the rail to droop under load.
3. Isolated DC-DC converter — a 1 W–3 W flyback that generates the internal 5 V and 3.3 V rails. This is the most common point of failure after a sustained overvoltage event (e.g., 24 V rail accidentally tied to 48 V or 60 V during commissioning).
4. Logic core — the LOGO! ASIC, Ethernet PHY, and SD card interface. These are powered from the 3.3 V rail. If the rail is missing, the device is electrically absent from any network.

None of the items above is field-serviceable. The Siemens repair strategy is full-unit replacement.

5. Step-by-Step Diagnostic Procedure

Work through the list in order. Each step eliminates one row of the symptom table from §3. Stop when the root cause is found.

5.1 Verify the 24 V DC supply at the LOGO! terminals

1. Power down the cabinet and lock out per local electrical safety rules.
2. Measure DC voltage directly across terminals L+ (+24 V) and M (0 V) with a calibrated DMM in V DC mode.
3. Acceptable range: 20.4 V to 28.8 V DC. A reading of 24.0 V ± 2 % is the design sweet spot.
4. Measure under load: re-energize and measure again. A reading that drops more than 3 % indicates an undersized PSU or excessive loop impedance on the 24 V wiring.

5.2 Measure the current draw

1. Insert a DMM in series with the L+ feed (use the 10 A range with a fused lead).
2. Apply power.
3. Compare the reading against the spec sheet (45 mA idle, 150 mA with display).
4. Interpretation:
   • < 5 mA: internal converter has failed to start — internal defect.
   • 45–200 mA: supply is reaching the internal rail — but if display is dark and link is down, the ASIC/PHY is not booting — internal defect.
   • > 500 mA: short-circuit fault on the internal rail — internal defect.
   • 0 mA but supply terminals at 24 V: open PTC inside the base — internal defect.

5.3 Reseat the display module

1. Power down.
2. Depress the display release tab on the underside and slide the display off.
3. Inspect the gold contact fingers for oxidation, dust, or bent pins. Clean with isopropyl alcohol and a lint-free swab if contaminated.
4. Re-seat firmly until the latch clicks. Power up and observe.

A LOGO! BM with a healthy core will still respond on Ethernet even if the display is fully removed. If link LEDs light up and the web server serves the default page at http://192.168.0.1, the display module is at fault — replace the LOGO! DM8 (6ED1055-1MB00-0BA2) or DM16 (6ED1055-1NB10-0BA2) and keep the original base.

5.4 Test Ethernet independently of the display

1. Connect a known-good patch cable from the LOGO! RJ45 to a laptop.
2. Configure the laptop NIC to 192.168.0.2 / 255.255.255.0.
3. Power up the LOGO!.
4. Observe the RJ45 LEDs. A healthy base shows a steady orange/green link LED within 5 seconds of power-up, even with no program loaded and no display attached.
5. Browse to http://192.168.0.1. The default LOGO! Web Server should appear.

If the link LED stays dark and ping 192.168.0.1 returns "Destination unreachable," the Ethernet PHY is unpowered — confirming an internal DC-DC failure.

5.5 Attempt a firmware recovery via micro SD card

Firmware recovery can rescue a base that boots far enough to run its bootloader, but no further:

1. Download the latest .IHD or .bin firmware from the Siemens LOGO! 8.2 support entry to a FAT32-formatted micro SD card (≤ 32 GB).
2. Insert the SD card into the base while it is powered off.
3. Hold the ESC and OK keys on the detached display (or simulate via LOGO! Soft Comfort) and apply power.
4. The base will enter recovery mode and reflash from the SD card. The process takes 60–180 seconds.

If the base does not show any reaction to the SD card insertion (no LED activity, no boot prompt), the internal 3.3 V rail is missing — recovery cannot proceed.

5.6 Bypass any external wiring

1. Disconnect every I/O terminal — I1–I8, Q1–Q4, and any expansion bus connector on the right-hand side.
2. Power the base from a laboratory 24 V supply (current-limited to 1 A) with no other conductors attached.
3. Observe current and link LEDs.

A shorted digital input (e.g., from a 24 V wire pinched to ground) or a welded relay contact can hold the internal rail in protection. A clean bench test isolates the base from all field wiring.

6. Root Cause Analysis

For the article number 6ED1052-1CC08-0BA0 with firmware V1.82.02 and the symptom set described, the field-proven root causes, ordered by frequency, are:

Items 1–4 are non-repairable at the board level by the user. Siemens' official position, confirmed in the LOGO! 8 Product Information, is replacement of the complete base module.

7. Resolution: Replacement and RMA

1. Record the serial number from the right-hand rating plate and the firmware version (V1.82.02 in this case).
2. Order a replacement base 6ED1052-1CC08-0BA0 from the authorized Siemens distributor where the original was purchased. Keep the proof of purchase with the serial number; it is required for warranty processing.
3. Before powering the new unit, verify that the 24 V supply is within spec and that the polarity is correct. Use a bench supply with current limiting for the first power-up.
4. Insert the original micro SD card (or re-export the program via LOGO! Soft Comfort) and download the project to the new base.
5. Reconnect I/O wiring, power up, and run the verification checks in §8.

If the unit is within the 24-month warranty window (standard for Siemens LOGO! 8 in most regions), contact Siemens Industry Online Support with the serial number, the firmware version, and a description of the failure mode to initiate an RMA. Siemens' standard warranty excludes damage from overvoltage, reverse polarity, mechanical impact, and operation outside the published environmental limits.

8. Verification

After installing the replacement base, perform the following functional checks:

1. Display test. The LOGO! splash screen appears within 3 s of power-up, followed by the status screen showing the program name, date, and time.
2. Input test. Force each of I1–I8 from a 24 V source. The corresponding input LED on the front of the base lights within 50 ms, and the input state is reflected in the LOGO! status menu.
3. Output test. In the LOGO! "Stop" mode, manually set each output Q1–Q4 to ON. The relay contacts close and the output LED lights. Use a DMM in continuity mode to confirm the contact resistance is < 50 mΩ on the NO contact and > 100 MΩ on the NC contact.
4. Ethernet test. Link LED is active within 5 s. Ping the base from a PC: ping 192.168.0.1 -t returns < 5 ms on a clean network.
5. Web server test. Browse to http://192.168.0.1; the default LOGO! Web Server landing page renders. Log in with the configured password (default: "LOGO").
6. Modbus TCP test. From a Modbus poll tool, read holding register 0 (VW0). The base responds with the configured value within 100 ms.
7. Power quality test. With the system running, log the 24 V supply over 24 h. The voltage must remain inside 20.4–28.8 V DC at all times. Any excursion outside that band is a likely contributor to the original failure and must be corrected before the new base is committed to service.

9. Preventive Measures

Field experience shows that single-point failures of the LOGO! 8 base are almost always secondary to a power-quality event. The following measures prevent recurrence:

10. Frequently Asked Questions