Troubleshooting PCS 7 Redundant Server Station Configuration

Problem Description: Cross-Write Between Redundant OS Servers in PCS 7

A symptom commonly reported in PCS 7 V8.x redundant operator station deployments is that configuration actions directed at the Master server (e.g., OSSRV1A) are silently applied to the Standby server (OSSRV1B), leaving the Master empty in the Station Configuration Editor (SCE). A second symptom is that the station name displayed inside the SCE flips from OSSRV1B to OSSRV1A after the second download, even though the engineer explicitly targeted OSSRV1A.

The reported sequence is:

1. Right-click OSSRV1B → PLC → Configure. Download completes in ~60 s. SCE on OSSRV1B shows CP 1613 at index 1 and WinCC Appl. (Stby) at index 2. Correct.
2. Right-click OSSRV1A → PLC → Configure. Download reports Transfer completed successfully. SCE on OSSRV1A is empty. SCE on OSSRV1B now shows OSSRV1A in the station field.

This pattern is observable in PCS 7 V7.1 through V9.0 SP3 when the engineering station and the two OS servers share a SIMATIC NET PC station that is still in a transient or partially initialized state, when the WinCC redundancy partner name does not match the SCE station name, or when NetPro IP address bindings collide between the two PC stations.

PCS 7 Redundant OS Server Architecture: Master / Standby Pair

A PCS 7 redundant operator system (OS) consists of two WinCC OS Servers that maintain identical process image and alarm logs. The redundancy model is:

• Master — actively archives, evaluates, and distributes process data to clients. The master is the primary write target.
• Standby — maintains a synchronized copy of all runtime data. On failure of the master, the standby promotes itself automatically within a configurable time (default ~3–15 s, depending on the WinCC redundancy tuning parameters).

Communication between the OS pair and the AS (Automation Station) family (e.g., AS 410, AS 400) is provided by a CP 1613 (PCI) or CP 1623 / CP 1628 (PCIe) communications processor installed in each server. These are Industrial Ethernet modules that terminate S7 connections and route process data through the SIMATIC NET OPC server and WinCC channel DLLs.

The SCE on each server must contain a consistent set of indices so that WinCC Runtime knows which logical slot corresponds to:

• Index 1 — the CP 1613 (or successor CP 162x) — handles S7/RFC 1006 communication to the AS.
• Index 2 — the WinCC Application (Stby) — the WinCC Runtime / Standby redundancy slot.
• Index 3+ — optional WinCC Application slot for the partner, OPC server slot, or additional applications.

Station Configuration Editor: Index Slots and Module Bindings

The Station Configuration Editor is the Windows-side instantiation of the PC station. It mirrors the configuration held in the STEP 7 / SIMATIC Manager project for that PC station. Each index entry binds a logical component to a physical interface on the server.

When you right-click a PC station in SIMATIC Manager and choose PLC → Configure, the engineering station pushes the SIMATIC PC configuration (the XML-like container stored in the project) to the running SCE service on the target server. The SCE service then re-binds the indices, restarts the WinCC Runtime, and writes the assignment to the Windows registry under HKLM\SOFTWARE\Siemens\SCE.

Root Cause Analysis

Cross-write of SCE configuration between two redundant OS servers is not a single fault. The four most frequent root causes are documented in the Siemens PCS 7 Compendium and the SIMATIC NET readme:

1. WinCC Redundancy Partner Name Mismatch

The WinCC redundancy configuration on the OS project contains the partner computer name. If OSSRV1A has its redundancy partner set to OSSRV1A (typo) and OSSRV1B has it set to OSSRV1A, the second download — regardless of which PC station is targeted — will bind to the only available matching host. Always verify under WinCC Explorer → Computer → Properties → Redundancy.

2. NetPro IP Address Collision or Wrong Binding

Both PC stations must have distinct IP addresses on the terminal bus and on the plant bus (if split). If OSSRV1A and OSSRV1B are configured with the same IP in NetPro, the SCE download will fail silently or, in older SCE versions, bind the configuration to the host that responds first to the broadcast lookup.

3. SIMATIC NET SCE Service Stale State

The SCE service (scSrvService or PNIO_SCE_Service depending on PCS 7 version) caches the last bound station name. If a previous engineer session left a stale binding — for example, after a master/standby role swap test — the next download can be intercepted by the wrong host. The SCE 8.1 readme notes that only fixed PROFIBUS bus profiles can be created for node initialization, which means user-defined bus profile changes from earlier projects can persist in the SCE cache.

Reference: SIMATIC NET SCE 8.1 Readme.

4. PCS 7 Project Duplicate PC Station Object

If the project contains a duplicate SIMATIC PC Station object (sometimes created when copying a server project and forgetting to rename the internal Name property), the download will resolve to the first matching object. The second download then re-targets the duplicate, which still points to the same physical host.

Prerequisites for Correcting the Configuration

1. SIMATIC Manager or PCS 7 Engineering Station installed, version matching the OS server image (V8.2, V9.0, V9.0 SP2, etc.).
2. Administrator credentials on both OSSRV1A and OSSRV1B.
3. SIMATIC NET PC software installed on the engineering station, including the SCE tool.
4. Network access to the terminal bus and plant bus; verify with ping from the engineering station to each server's plant bus IP.
5. WinCC Explorer available on both servers (locally, not via RDP) to verify redundancy partner assignment.

Step-by-Step Resolution Procedure

Step 1 — Stop WinCC Runtime on Both Servers

On each OS server, open WinCC Explorer and choose Stop Runtime, or stop the service CCAlgRtServer via services.msc. This prevents the SCE download from being intercepted by an active runtime that holds the registry binding open.

Step 2 — Verify and Correct NetPro IP Addresses

In SIMATIC Manager, open NetPro. For each PC station OSSRV1A and OSSRV1B:

1. Open Properties on the CP 1613 / CP 1623 in the station window.
2. Confirm the IP address is unique, e.g. OSSRV1A = 140.80.10.11, OSSRV1B = 140.80.10.12, subnet mask 255.255.255.0.
3. Confirm the S7 subnet assigned to the CP matches the plant bus (Industrial Ethernet subnet ID).
4. Compile and download NetPro to both stations. The Target System → Compile and Download Objects menu in NetPro must report Transfer OK for both.

Step 3 — Verify WinCC Redundancy Partner Names

On each server, open WinCC Explorer → Computer → Properties → Redundancy:

• OSSRV1A — partner computer name must read OSSRV1B.
• OSSRV1B — partner computer name must read OSSRV1A.

Correct any typo and save. Repeat the redundancy check in the OS project editor on the engineering station (the project-side redundancy must agree with the runtime-side redundancy).

Step 4 — Clear the SCE Cache on Both Servers

On each server:

1. Open the Windows registry editor (regedit) as administrator.
2. Navigate to HKLM\SOFTWARE\Siemens\SCE and export the key as a backup.
3. Stop the SCE service: net stop "SCE Service" or via services.msc.
4. Delete the StationName and IndexTable values.
5. Start the SCE service: net start "SCE Service".

Step 5 — Download the PC Station Configuration

On the engineering station, in SIMATIC Manager:

1. Right-click OSSRV1B → PLC → Configure. Wait for the Transfer completed successfully message.
2. Open the SCE on OSSRV1B locally and verify CP 1613 at index 1 and WinCC Appl. (Stby) at index 2.
3. Right-click OSSRV1A → PLC → Configure. Wait for Transfer completed successfully.
4. Open the SCE on OSSRV1A locally. It must now show CP 1613 at index 1 and WinCC Appl. (Stby) at index 2 with the station name OSSRV1A.
5. Open the SCE on OSSRV1B again and confirm the station name still reads OSSRV1B (it should not have flipped).

Step 6 — Restart WinCC Runtime and Verify Redundancy

On each server, start the WinCC Runtime. The Redundancy Control diagnostics view (start menu → SIMATIC → WinCC → Redundancy Control) should report:

• One server reports state Master, the other reports Standby.
• Both servers report a healthy partner connection (no Partner not reachable alarm).
• Archive synchronization settles within the configured timeout (default 60 s).

Alternative Download via HW Config

If the SIMATIC Manager PLC → Configure command continues to misroute, fall back to HW Config:

1. Open HW Config for the OS server PC station.
2. Choose PLC → Download to Target System.
3. In the Select Target System dialog, choose Accessible Nodes and confirm the target node MAC address matches the CP 1613 of the intended server.
4. Complete the download. The HW Config path uses the MAC address of the CP as the routing key, which is more deterministic than the SCE broadcast lookup.

This is the method recommended in the PCS 7 Compendium Part A Configuration Guidelines, Chapter 3, for AS/PC station configuration.

Verification Checklist

Troubleshooting Matrix

Reference to PCS 7 Configuration Guidelines

The PCS 7 Compendium Part A — Configuration Guidelines, Chapter 3 (AS/PC Station Configuration) is the canonical reference for setting up redundant OS server pairs. The compendium specifies that the engineer must:

• Define the terminal bus and plant bus topology before any PC station is created.
• Reserve CP 1613 / CP 1623 as the first index of every PC station.
• Configure the WinCC redundancy in the OS project first, then the PC station, then download.
• Use Compile and Download Objects from NetPro as the primary download mechanism; use PLC → Configure as a secondary verification step.

Notes on PCS 7 V8.x SCE Behavior

The SIMATIC NET SCE 8.1 readme documents that only fixed PROFIBUS bus profiles can be created for node initialization. This means that when the SCE initializes a station, it expects a fixed bus profile — user-defined profiles from older projects are not preserved across SCE resets. The practical implication for the cross-write symptom is that any non-standard bus profile on the standby server may not be reflected in the SCE after a master download, causing the SCE to fall back to a default profile that binds to the wrong host. Always reset both servers to the default profile before downloading.

Recovery After Persistent Failure

If the symptom returns after the standard procedure, escalate as follows:

1. Export the full PCS 7 project: File → Archive → User-defined archive.
2. Use Station Configuration Editor → Diagnostics → Read Out Station on both servers and compare the resulting XML files.
3. Reinstall the SIMATIC NET PC software on both servers (maintain the same version as the engineering station, e.g., V14 SP1 for PCS 7 V8.2, V15.1 for V9.0).
4. Re-import the project and rebuild the PC station configuration from scratch.
5. As a last resort, recreate the PC station objects in the project: Insert → Station → SIMATIC PC Station, then rebuild the HW Config and NetPro entries.

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