Troubleshooting Grayed-Out 'Changes Only' Option in SIMATIC PCS 7 WinCC OS Download

In SIMATIC PCS 7, when the 'Changes' (delta download) option is grayed out or disabled in the OS Download dialog, forcing 'Download entire WinCC project', the cause is a broken delta tracking baseline. The engineering system disables delta download when: manual configuration changes were made directly inside the target OS project rather than compiled from the ES, 'Delta Save' is deactivated in Picture Tree Manager, redundant OS servers are in a split or desynchronized state, or local compilation cache files are inconsistent. To restore delta capability, perform a complete download ('Download entire WinCC project') during a planned maintenance window to re-establish the baseline.

Executive Summary

In 24/7 operating process facilities, online delta downloads ('Changes only') of WinCC Operator Stations are critical to deploying screen updates and tag modifications without stopping operator monitoring. When engineers attempt an OS download and discover that 'Changes' is grayed out—leaving only 'Download entire WinCC project' selectable—initiating the download will stop WinCC Runtime, blind operator displays, and interrupt alarm logging. This guide analyzes the architectural conditions that break WinCC delta tracking, details configuration settings in Picture Tree Manager, and provides best practices to maintain delta download readiness.

Architecture and Fundamental Mechanics

The PCS 7 OS Delta Download architecture depends on cryptographic database journaling:
1. Delta Tracking Journaling:
When an OS is compiled on the ES, Step 7 records a compilation transaction signature. During a download with 'Changes only', the ES compares this signature with the runtime signature stored on the target OS. Only modified graphic pictures (.pdl), modified C/VBS scripts, and updated tag tables are transmitted over the Terminal Bus.
2. Invalidation Triggers for Delta Download:
- Local Target Modifications: If any engineer opens WinCC Explorer directly on the OS server and edits a picture, tag, or script, the target database signature diverges from the ES baseline. The ES detects the divergence and permanently locks out delta downloads to prevent database corruption.
- Picture Tree Manager Configuration: If 'Delta Save' is unchecked in Picture Tree Manager options, every save operation forces a total recalculation of group display hierarchies, invalidating incremental screen updates.
- Redundant Server Synchronization Split: If Server 1 and Server 2 have different project revisions (e.g., after one server was restored from a backup image), the ES prevents delta download until both servers are aligned via a full project download.
- Corrupted Local Cache: If temporary files (*.dcf or *.pck) on the ES become corrupted, the delta compiler cannot determine the differential changeset.

Step-by-Step Implementation Procedure

Verify Picture Tree Manager Delta Save Setting:
a. On the Engineering Station, open the OS project in WinCC Explorer.
b. Open 'Picture Tree Manager'.
c. Select Options -> Settings.
d. Ensure that the checkbox 'Delta Save' is checked.
e. Save and close Picture Tree Manager.
Check Redundant Server Synchronization Status:
a. On both OS Server 1 and OS Server 2, check the WinCC Redundancy status dialog.
b. Verify that redundancy is operational and that neither server is in an isolated fault state.
c. Confirm that internal tags @RM_MASTER and @RM_SERVER_STATE are healthy on both nodes.
Execute Complete Compilation on the ES:
a. In SIMATIC Manager, right-click the OS object and select Compile.
b. Select 'Entire OS' to re-index all tags, messages, and graphic hierarchy tables.
c. Ensure compilation finishes with 0 errors.
Perform Baseline Full Project Download (Maintenance Window):
a. When the 'Changes' option is permanently locked out, a full download is mandatory to reset the tracking baseline.
b. Schedule a suitable maintenance window.
c. In SIMATIC Manager, right-click the OS station and select PLC -> Download.
d. Select 'Download entire WinCC project'.
e. If downloading to a redundant server pair, download to the standby server first, verify runtime startup, execute redundancy synchronization, and then download to the partner server.
Test Subsequent Delta Download:
a. Modify a single graphic picture or add an internal tag on the ES.
b. Compile OS with 'Changes only'.
c. Open the Download dialog: verify that the 'Changes' radio button is now fully active and selectable.

Verification

In SIMATIC Manager, right-click the OS object and choose PLC -> Download.
Confirm that the 'Changes' option is selectable (radio button enabled).
Execute a delta download: confirm that the transfer completes in seconds without stopping WinCC Runtime on the target server.
Verify on the target OS that modified screens update seamlessly and active alarms remain uninterrupted.

Limitations and Operational Precautions

Certain structural changes—such as modifying Tag Logging archive segment sizes, altering computer names, or changing redundant partner definitions—always inherently require a complete download and cannot be deployed via delta download under any circumstances.

Engineer FAQ

Why is 'Changes only' grayed out in the OS download dialog?

Because the delta tracking baseline between the ES and OS was broken by local modifications on the server, corrupted cache, or uncoordinated database changes.

Can I restore the 'Changes' option without a full project download?

Generally no. Once the database transaction signature is broken, only a full project download ('Download entire WinCC project') can re-establish the baseline.

Does Picture Tree Manager affect delta downloads?

Yes. If 'Delta Save' is disabled in Picture Tree Manager, delta screen updates are blocked, forcing total project deployment.

How do I perform a full download on redundant servers without plant downtime?

Download to the standby server first while the master keeps running. Once the standby restarts and synchronizes, switch operator clients to it and download to the master server.

Can I manually copy a modified .pdl file instead of downloading?

For emergency graphics changes, copying the .pdl file directly to the OS GraCS directory works, but it does not update database tags and does not re-enable the delta download wizard.