Resolving WinCC Advanced RT Full Screen Loss on Remote Desktop

When a Windows 7 Pro host running WinCC Advanced Runtime (RT) v13 SP1 Update 7 under TIA Portal is taken over with Remote Desktop Connection (RDC / mstsc.exe), VNC, or RAdmin, the Runtime window drops out of full-screen mode. The Windows taskbar reappears at the bottom of the screen, and the Runtime no longer occupies the entire display. The condition persists after the remote session is terminated; only a manual restart of WinCC RT restores the full-screen layout. The same panel that runs under TeamViewer is unaffected, but TeamViewer's per-seat licensing is often not justifiable for engineering or service access only.

This article documents the underlying cause, the two field-proven resolutions, and the workarounds that have been used on production machines. It also lists the SetDisplayMode limitation and the exact registry / configuration changes that keep the Runtime in full-screen mode across inbound remote sessions.

1. Problem Statement

Symptom. WinCC Advanced Runtime is configured for full-screen operation in the TIA Portal project. The "Full-screen mode" and "Lock task switching" options are both enabled in the Runtime settings. On local console use the Runtime occupies the entire primary display. As soon as an engineer or service technician opens a Remote Desktop session, attaches a VNC viewer, or connects with RAdmin:

1. The Windows taskbar appears.
2. WinCC Advanced Runtime exits full-screen and resizes to a windowed layout.
3. The minimize, maximize, and close buttons become non-functional.
4. When the remote session ends, Runtime stays in windowed mode; the taskbar stays visible.
5. Only a full restart of RTIL.exe (WinCC Advanced Runtime loader) restores full-screen.

Affected software.

• WinCC Advanced RT v13 SP1 Update 7 (part of TIA Portal V13 SP1)
• Operating System: Windows 7 Professional (x64) with Aero theme enabled
• Remote clients tested: Microsoft Remote Desktop Connection (mstsc.exe), RealVNC Viewer, TightVNC, RAdmin 3.x
• Remote clients that work without modification: TeamViewer (licensed per seat)

Business impact. Operators lose the locked-down single-purpose HMI behaviour that the "Lock task switching" flag is meant to provide. The Windows desktop is exposed, allowing accidental termination of Runtime, file-system access, or launch of unrelated applications while a remote engineer is connected.

2. Root Cause Analysis

The dominant root cause is a Windows 7 theme switch triggered by inbound Remote Desktop sessions.

When a remote session is negotiated with a client that does not advertise full RemoteFX / Aero redirection capability, the Windows 7 host switches the active visual theme from Windows 7 Aero to Windows 7 Basic for the duration of the session. The theme reverts when the session ends. WinCC Advanced Runtime is built against the Aero presentation layer; on the theme switch it receives a window-style change message that causes the Runtime main window to drop out of exclusive full-screen state into a regular overlapped window. Because the same window class is reused after the session is closed, the Runtime does not automatically restore its previous maximized / exclusive state.

This behaviour is documented in Microsoft support material for similar Remote Desktop display issues (Microsoft Learn: Can't maximize RDC session window to full-screen) and is consistent with the field experience reproduced on the affected WinCC Runtime host.

Secondary contributors observed on the same hardware image:

• VNC viewers using CaptureMode = 0 (default) inject a virtual display driver hook that also forces Win32 windows out of exclusive full-screen.
• RAdmin uses a mirror driver that triggers the same theme-downgrade as RDP.
• TeamViewer uses a frame-buffer capture that does not interact with the host window manager, hence Runtime is not disturbed.

3. Solution A — Disable Aero, Use Windows Classic Theme

This is the cheapest and most reliable fix. Switching the host theme to Windows Classic removes the Aero DWM layer that is the source of the theme-switch side effect on RDC and RAdmin attach.

3.1 Apply the theme on the host

1. Log on to the WinCC Advanced Runtime PC at the physical console with administrator credentials.
2. Right-click Desktop > Personalize.
3. Select Windows Classic from the list of themes.
4. Click Apply, then OK.
5. Reboot to make the theme selection permanent for the auto-logon operator account.

3.2 Verify Runtime settings still match the TIA Portal project

Confirm in the TIA Portal project that Runtime settings > Screen > Full-screen mode and Runtime settings > Screen > Lock task switching remain enabled. The TIA Portal V13 SP1 documentation describes these options under Configuring display in Runtime - WinCC; the option semantics are identical from V13 through V20.

3.3 Re-test

1. Start WinCC Advanced Runtime, confirm full-screen display.
2. From a remote client, launch Remote Desktop Connection and connect.
3. Confirm Runtime remains full-screen during the active session.
4. Disconnect the session.
5. Confirm Runtime remains full-screen after disconnect; no manual restart required.

Result on the affected hardware. With Windows Classic theme enabled, RDC and RAdmin attach/detach events no longer alter the Runtime window state. The trade-off is the loss of Aero visual effects on the operator desktop; for a single-purpose Runtime host this is normally acceptable.

4. Solution B — RealVNC With CaptureMode = 1

If the customer requires a richer desktop theme or needs VNC for cross-platform access, RealVNC Server can be configured so its screen-capture mechanism does not break the host's full-screen Runtime window.

4.1 Required software

• RealVNC Server 5.x or 6.x (Free or Personal license tier is sufficient for the CaptureMode override; Enterprise tier is required for the Expert tab UI in some builds).
• RealVNC Viewer on the remote client.

4.2 Configure CaptureMode

1. On the WinCC host, right-click the RealVNC Server tray icon and choose Options.
2. If the dialog only shows Basic settings, hold Shift while clicking Options to unlock the expert configuration tree.
3. Navigate to Expert > CaptureMethod (or Capture > CaptureMethod depending on build).
4. Set the value to 1 (mirror driver disabled; polling-based capture).
5. Click Apply and restart the RealVNC Server service.

4.3 Verification

1. Start WinCC Advanced Runtime in full-screen.
2. Connect from a remote client with RealVNC Viewer.
3. Disconnect.
4. Confirm Runtime is still in full-screen state and the taskbar is not visible.

5. Workaround — Kill explorer.exe to Hide the Taskbar

If neither of the above is acceptable, the taskbar can be removed by terminating the Windows shell process. This is a hostile-user workaround and should be combined with administrative authentication on Runtime to prevent operators from re-launching explorer.exe.

5.1 VBScript snippet for WinCC Advanced

WinCC Advanced Runtime only supports VBScript (not C-script). Place the following script behind an event that fires once at Runtime start, e.g. the Opened event of the start screen or a scheduled task in the Windows scheduler triggered by WinCC startup.

' KillExplorer.vbs
' Removes the Windows shell / taskbar. Use with caution.
Option Explicit

Dim objShell
Set objShell = CreateObject("WScript.Shell")

' Terminate explorer.exe on the interactive session
objShell.Run "taskkill /F /IM explorer.exe", 0, True

Set objShell = Nothing

5.2 Restoring explorer.exe (administrative button)

Provide an HMI button that is only enabled when an operator with the correct user group is logged in. The button triggers:

' RestartExplorer.vbs
Option Explicit

Dim objShell
Set objShell = CreateObject("WScript.Shell")

objShell.Run "explorer.exe", 1, False

Set objShell = Nothing

5.3 Caveats

• If the Runtime crashes, the desktop remains shell-less; technicians must launch explorer.exe from Task Manager > File > Run to restore the shell.
• Some OEM management agents and printer tray icons depend on explorer.exe and will not load.
• This is a mitigation only — it hides the taskbar but does not fix the underlying Runtime full-screen state loss.

6. SetDisplayMode System Function — Why It Is Not a Cure

The TIA Portal system function SetDisplayMode can be scripted from the start screen or invoked on a tag change. Calling SetDisplayMode with parameter value 2 (Full screen) re-asserts the Runtime full-screen state. In practice it has two field-proven problems:

1. Focus theft. The Runtime main window receives a WM_ACTIVATE / WM_SETFOCUS side-effect that cancels any input currently being entered into an I/O field. If a tag change triggers the call while an operator is typing a setpoint, the entry is lost.
2. Re-arm requirement. After every RDC attach/detach pair a new invocation is needed. A polled tag with a 5-minute timeout pattern works but is fragile.

6.1 Polled re-arm (acceptable only as a belt-and-braces)

' On the start screen, schedule a cyclic event:
' Cycle: 5 minutes
' Event: Run script
' Script body:
SetDisplayMode 2   ' Full screen

This works only as a tertiary safeguard on top of Solution A or Solution B, not as the primary fix.

7. Alternative Architectures

8. Verification Matrix

9. Troubleshooting Matrix

10. Group Policy Lock-Down (Recommended Add-On)

To prevent operators or RDP users from reverting the Windows Classic theme and re-introducing the issue, lock the theme selection through Group Policy:

1. Open gpedit.msc on the host (or push via Active Directory GPO).
2. Navigate to User Configuration > Administrative Templates > Control Panel > Personalization.
3. Enable Prevent changing theme.
4. Navigate to User Configuration > Administrative Templates > Control Panel > Personalization > Desktop.
5. Enable Prevent changing desktop background (optional, to lock down the operator UI).
6. Run gpupdate /force from an elevated command prompt.

This blocks the theme from being switched back to Aero by an operator with local access, securing the resolution permanently.

11. Related Settings in TIA Portal

To harden Runtime against accidental mode changes regardless of the remote access path, verify the following in the project:

The settings above align with the documented WinCC configuration options described in Configuring display in Runtime - WinCC.

12. FAQ