Fixing LOGO! 8.3 Connection Errors with LOGO!Soft Comfort 8.3.1

Fixing LOGO! 8.3 Connection Errors with LOGO!Soft Comfort 8.3.1

This technical reference documents the diagnostic workflow and corrective actions for Ethernet communication failures between a Siemens LOGO! 8.3 basic module (firmware 1.83.02) and LOGO!Soft Comfort V8.3.1. The failure pattern addressed here is the most common field complaint: every LOGO! device on the LAN is visible to the LSC network browser, the LSC "Go Online" status returns devices, yet the program download fails, the connection drops during transfer, or LSC refuses to commit the new configuration to the LOGO! 8.3 BM. The same procedure applies whether the previous LSC install was V7.0/V7.1 or an earlier V8.x build.

1. LOGO! 8.3 Communication Architecture

Understanding the network stack used by LOGO! 8.3 prevents misdiagnosis. The BM (basic module) integrates a 10/100 Mbit/s Ethernet interface on the left-hand RJ45 port. Communication occurs over four distinct channels, each with its own TCP/UDP port:

LOGO!Soft Comfort V8.3.1 uses port 10005 for the bulk of its transfer operations and port 102 for the S7 read/write used during online mode. A failed transfer with the dialog "Cannot connect to LOGO!" or "Connection interrupted during write" indicates either port 10005 or port 102 is being filtered, blocked, or held by another process.

2. Symptom Matrix

Before applying any fix, classify the failure mode. Each row in the matrix below corresponds to a distinct root-cause family.

3. Prerequisites for Diagnosis

1. Local administrator rights on the engineering PC (required for firewall, NIC driver, and ARP cache operations).
2. LOGO!Soft Comfort V8.3.1 (build 8.3.1.0 or later; verify via Help > About).
3. LOGO! 8.3 BM firmware 1.83.02 (verify on the BM display: Menu > Diagnostics > Firmware, or via the web UI at https://<IP>:8443).
4. Known-good patch or crossover cable (Cat 5e or better).
5. A spare unmanaged 100 Mbit/s switch for isolation tests.
6. Static IP plan for the LOGO! network (out-of-DHCP-pool).

4. Step-by-Step Diagnostic Procedure

Step 4.1 — Validate LOGO! 8.3 IP Address

Open the BM display and navigate Menu > Network > IP Address. Note the four octets and the subnet mask (default: 255.255.255.0). Confirm:

• The address is outside the router's DHCP pool (typically a router issues 192.168.0.100–192.168.0.254; place LOGO! in 192.168.0.2–192.168.0.99).
• No other LOGO! shares the same address. Run on the PC:

  arp -a | findstr "<IP-of-LOGO>"

  If the MAC returned is not the Siemens MAC (prefix 00-0E-8C or similar), a duplicate exists.

Step 4.2 — Disable DHCP on the BM

On the BM display: Menu > Network > DHCP > No. Repeat for each LOGO! 8.3 BM on the segment. The DHCP state is volatile across BM power-cycles only if the firmware was upgraded mid-session; perform a power-cycle after toggling to ensure the new state is committed to flash.

Step 4.3 — Verify Subnet Consistency

Every device that must communicate must share the same subnet mask. A common field error is a LOGO! at 192.168.0.10/24 and a PC at 192.168.1.20/24 — both fall in 192.168.x.x and pass naive visual inspection but are on different Layer 3 networks.

On the PC, run:

ipconfig /all

Compare the PC's IPv4 address, subnet mask, and default gateway against the LOGO! settings. All three must be consistent across the engineering PC and every LOGO! BM that must be reached.

Step 4.4 — Test Point-to-Point Connectivity

1. Disconnect the LOGO! 8.3 BM from the plant LAN.
2. Connect the BM directly to the PC using a patch cable (modern PCs auto-negotiate MDI/MDIX; no crossover required).
3. Assign the PC a static address in the same subnet, e.g. 192.168.0.50/24.
4. Ping the LOGO!:

   ping 192.168.0.10

   A successful round trip with TTL ~64 confirms Layer 2/3 reachability independent of switches, routers, and DHCP.

If the ping fails point-to-point, the issue is at the BM or PC NIC — proceed to Step 4.5. If the ping succeeds point-to-point but fails on the LAN, the issue is at the switch or router — proceed to Step 4.6.

Step 4.5 — Reset LOGO! 8.3 to Factory Defaults

Hold the ESC and OK buttons on the BM during power-up. The display will prompt Reset to factory defaults?. Press OK to confirm. This clears IP, subnet, DHCP, web-server passwords, and program storage. Reapply the IP configuration after the reset. The BM will reboot in ~30 s.

Step 4.6 — Inspect Managed Switch / Router

If point-to-point is healthy but LAN is broken, the managed switch or router is the suspect. Verify:

• Port security: Disable 802.1X authentication or pre-register the BM MAC in the allowed-MAC table.
• VLAN membership: The BM port and PC port must be in the same VLAN (or VLAN trunking must pass the BM's VLAN tag).
• Multicast / IGMP snooping: LSC discovery uses a limited broadcast. Excessive IGMP snooping on some HP/Aruba switches has been observed to drop the LSC probe packet.
• ACL / Firewall rules: Block on TCP 10005 is rare but exists on locked-down industrial firewalls.

Step 4.7 — Validate Windows Network Profile

Windows 10 and Windows 11 default to the Public network profile on first connection to a new SSID or wired segment. The Public profile blocks inbound discovery and disables file/printer sharing. Open Settings > Network & Internet > Ethernet and confirm the profile reads Private. Also verify:

Get-NetFirewallProfile -Name Public | Select Enabled, DefaultInboundAction
Get-NetFirewallProfile -Name Private | Select Enabled, DefaultInboundAction

The Private profile inbound action should be NotConfigured or Allow; the Public profile should remain Block.

Step 4.8 — Configure Windows Firewall Rules for LSC

Even with firewall fully disabled, third-party security products (Symantec, McAfee, Trend Micro, Kaspersky) re-enable protection at the NDIS level. Open wf.msc and create two explicit rules:

1. Inbound rule: Allow TCP 10005 — program path %ProgramFiles%\Siemens\LOGOComfort_V8\LOGOComfort.exe.
2. Inbound rule: Allow TCP 102 — same program path.

If using a third-party endpoint protection suite, add LSC and its dependent s7otbxdx.dll process to the application allow-list. A common field symptom is the firewall disabled in Windows Defender but active in the third-party product, producing the same transfer failure.

5. LOGO!Soft Comfort V8.3.1 License Validation

The most overlooked cause of "connection seems to work but won't commit" is a license downgrade. LOGO!Soft Comfort V7.x full licenses do not auto-migrate to V8.x; they must be re-activated via the Siemens License Server or the License Key USB stick that shipped with the V7.x purchase.

Verify license state

1. Open LSC V8.3.1.
2. Click Help > About LOGO!Soft Comfort.
3. Inspect the line "License:" — it must read Full Version, not "Trial" or "Demo".
4. Click "Activate License" if the field shows "Not Activated". Provide the license key from the original V7.x Certificate of License (CoL) or the License Key USB stick.

If the V7.x install was a demo, the upgrade to V8.x is also a demo. Demo builds of LSC can browse the network and enter online mode but cannot download programs to a BM with firmware > 1.82.00. The BM display will show STOP after the transfer attempt because the program was rejected at the BM level (BMs reject non-licensed program images).

6. Program Transfer Procedure (Verified)

1. Open the program in LSC V8.3.1.
2. Click Tools > Transfer > PC → LOGO! (or press Ctrl+D).
3. Select the target BM from the dialog. The IP, BM type, and firmware are displayed. If the firmware shows 1.83.02 and the program is older, LSC will offer to recompile — accept.
4. Choose the transfer mode: Stop LOGO! (RUN → STOP → RUN). This is the safe path. The other option, RUN → RUN, requires the program signatures to be byte-identical except for variable values.
5. Click "Transfer". A progress bar appears; the BM display reads PC<->LOGO!. Transfer of a typical 200-block program completes in 5–15 s.
6. Confirm with OK on the BM display when prompted, then click "Start LOGO!" in LSC.

7. Web Server Verification (Alternate Path)

If LSC continues to refuse connection despite the fixes above, validate end-to-end IP reachability via the LOGO! web UI:

1. Open a browser and navigate to https://192.168.0.10:8443 (replace IP with the BM's actual address).
2. Accept the self-signed certificate warning.
3. Default credentials: user LOGO, password LOGO (factory default; change on first login via the Web UI).
4. Inspect the Diagnostics page — note any active error codes. Common 8.3 firmware 1.83.02 codes:

If the web UI loads but LSC still fails, the S7/LSC protocol path (port 102/10005) is broken while the HTTPS path (port 8443) is healthy — strongly indicating a firewall or third-party security product block.

8. Firmware Compatibility Matrix

9. SD Card Firmware Update Procedure

1. Obtain the firmware file LOGO8_3_BM_V18402.zip from the Siemens Industry Online Support portal.
2. Extract the .upd file to a microSD card (FAT32, <32 GB recommended).
3. Power off the BM, insert the SD card.
4. Hold the OK button during power-on. The display shows the firmware file from the SD card.
5. Press OK to confirm. The update runs in ~90 s. Do not interrupt power.
6. After the BM reboots, verify firmware on the display or via the web UI.

10. Verification Checklist

11. Edge Cases and Field-Proven Caveats

• Multiple NICs: PCs with both Ethernet and Wi-Fi active can route LSC traffic out the wrong NIC. Disable Wi-Fi during transfer or set the NIC metric so the wired interface is preferred.
• VPN client: Cisco AnyConnect, FortiClient, and Zscaler insert virtual NICs that can intercept TCP 10005. Disconnect the VPN before transferring.
• Docker / WSL: Hyper-V virtual switches and WSL2 vNICs can claim the 192.168.0.0/24 range, blocking LSC. Disable Hyper-V WSL integration or set the LSC to use a specific NIC.
• Dual-stack IPv6/IPv4: Some LSC builds attempt IPv6 first; if IPv6 routing is broken, transfer hangs. Force IPv4 with the LSC option Use IPv4 only in Tools > Options > Connection.
• Time skew: LSC rejects connections from PCs whose clock is >5 minutes off the BM clock. Synchronize both to NTP before commissioning.

12. Frequently Asked Questions