Resolving Siemens MP 377 15-inch Touch Panel Freeze Issues

1. Problem Summary

The SIMATIC MP 377 15" Touch Multi Panel, when running a WinCC Flexible 2007 Advanced HF4 runtime, freezes on the operator's request to change pages. The display continues to render the previously active screen, places a centered hourglass / wait cursor over it, and queues subsequent touch input. The ActivatePage call that drives the page change eventually returns — sometimes after 5 minutes, sometimes after 30 minutes — but the panel is operationally dead for the duration. In the documented field case, the fault reappeared on a warranty replacement unit, and a primary download on the second unit aborted mid-write, leaving the device unbootable with an "Image file corrupted" message.

This class of fault is not unique to a single batch. Siemens support bulletins for the MP 277 / MP 377 generation document comparable runtime stalls, image-write failures, and remote-session lockups across several firmware revisions; many are addressed by service pack updates and by the revised ProSave / Automation License Manager (ALM) toolchain. Before escalating as a hardware defect, the project itself must be ruled out using a controlled test method.

2. Affected Hardware and Software Stack

For the most current device manual, refer to the Siemens Industry Online Support entry for the MP 377 15" Touch at SIMATIC HMI device MP 377. WinCC Flexible 2007 documentation is collected at WinCC Flexible 2007 manual collection.

3. Symptom Matrix

4. Root Cause Hypotheses

Five independent causes produce the exact symptoms above. They are listed in the order in which they should be ruled out before any RMA is raised.

4.1 Excess picture / object count on the destination page

WinCC Flexible 2007 caches compiled pages in working memory. A page that contains large bitmaps, many I/O fields, or dozens of polygon-pipe animations forces the page-buffer allocator to swap aggressively. Combined with even a single "Change Value" script that traverses the tag list, page-change latency can climb from sub-second to several minutes. The pipe-coloring logic described in the field case is exactly this pattern. Mitigated by splitting the page, by reducing bitmap resolution to indexed 256-color BMP/PNG, and by removing stacked animations.

4.2 Scripts attached to "Change Value" with synchronous I/O

The runtime executes Change Value scripts in the same thread that services the page-flip event. A script that does long arithmetic, string manipulation, or — most damaging — reads or writes a large tag block in one call can starve the page-flip dispatcher. The two color-change scripts in the field project are exactly this pattern. Mitigation options: convert the script to a scheduled task with a 250 ms cycle, or move the logic into a Step 7 FB on the S7-300 and let the panel simply read the result tag.

4.3 Sm@rtService / Internet Explorer residual session

The MP 377 supports remote operation through Sm@rtService over HTTP. If a remote browser session is closed without first selecting "Logoff" on the operator page — or by killing the browser process directly — the runtime leaves a phantom session token. Subsequent local touches are processed against the remote-user context and may queue indefinitely. A power-cycle is required to clear the token table. The Sm@rtService daemon clears tokens only at boot.

4.4 Image file corruption from interrupted OS update

ProSave "Update OS" (also called "Primary Download" in older toolchains) writes the WinCE 5.0 image and the runtime in two passes. A power loss, a USB cable pull, or a service tool crash between the two passes leaves the flash with a half-written image; the bootloader detects the CRC mismatch and stops with the "Image file corrupted" prompt. Re-running the primary download with the panel on a UPS and on a stable USB or Ethernet connection resolves it in roughly 12 minutes.

4.5 Defective flash on a single unit

If a replacement unit reproduces the same fault on a minimal test project with no scripts and small bitmaps, the panel itself is suspect. RMA escalation with the service tag and a ProSave backup attached is the proper channel. A panel that aborts two consecutive ProSave primary downloads is no longer serviceable in the field.

5. Step-by-Step Diagnostic Procedure

Follow this exact sequence. Do not skip steps; each gates the next.

1. Capture the project from the panel: ProSave → Backup → *.psb. Store offline. Archive the license file via ALM on the engineering PC.
2. Disable all remote access: Control Panel → Sm@rtService → "Remote control" set to Off. Reboot the panel.
3. Re-test page changes for 30 minutes. If the fault clears, the cause is section 4.3 — stop and apply Solution E.
4. Open the original *.hmi in WinCC Flexible 2007. Compile → Start Runtime Simulation. Re-test page changes for 30 minutes.
5. If the simulation freezes identically, the project is guilty (section 4.1 / 4.2). Apply Solutions A and B.
6. If the simulation runs cleanly, the panel is guilty. Build a minimal test project: 3 pages, 1 navigation button per page, 5 tags, 0 scripts. Transfer to the panel. Cycle page 50 times manually. Measure response.
7. If the minimal project also freezes the panel, escalate to firmware / hardware. Apply Solution D first; if the firmware update fails twice, RMA.

6. Solution A — Reduce Script and Picture Load

The two "change color" scripts in the field project are the most likely accelerant. Move them off the panel and onto the PLC. On the S7-300 side, the pipe-segment color can be computed in a single FB that takes the segment state and writes the corresponding W#16# color word into a tag array of type WORD. The panel reads the color tag and applies it to the pipe object via the standard Animation → Appearance interface. This removes the Change Value script entirely.

For the picture-side reduction:

• Replace any BMP larger than 200 x 200 px with a 256-color indexed PNG. The MP 377 display is XGA; anything larger is downscaled at compile time and burns flash for no visual gain.
• Combine adjacent static pipes into a single graphic with multiple colored segments drawn at compile time.
• Use the "Layer" field on each animation only if you actually overlap animations; otherwise clear it.
• Verify compiled size: in WinCC Flexible, Project → Compiler → Output. If the *.fwx exceeds 8 MB, expect measurable page-load latency on a 15" panel; above 10 MB the runtime becomes unreliable.

7. Solution B — Event and Tag Audit

Open the project and produce a Tag + Cross-reference report. For every "Change Value" event, document:

• Tag name and data type
• Acquisition cycle (default 1 s — increase to 2 s for non-critical tags)
• Script length and any internal loops
• Limit value / upper / lower scale that re-triggers the event

If a tag's value is set to its current value, WinCC Flexible still fires the Change Value event by default. Force the limit check box in the tag properties to "Quality code" only, or wrap writes in a debounce FB on the PLC side. For S7 connections, set the acquisition mode to "Cyclic continuous" only where the value genuinely changes faster than 2 s.

For scheduled tasks, audit the cycle time. A 100 ms cycle that runs a script with five tag reads against a 1.5 MB pipe picture will use 100 % of the runtime thread and starve the page-flip handler. Lower the cycle to 1 s for animation tasks and never schedule a script faster than 250 ms.

8. Solution C — Convert Runtime to PC for Verification

This is the single fastest way to prove whether the panel or the project is the fault. In WinCC Flexible 2007:

1. Project → Device type → Change device type…
2. Select "WinCC Flexible RT" on a Windows PC.
3. Compile, transfer the *.fwx to a notebook running the WinCC Flexible 2007 runtime.
4. Connect the notebook to the S7-300 via an MPI/PC adapter (e.g. 6ES7 972-0CA23-0XA0) or via Ethernet CP, using the same tag list and the same MPI address the panel used.
5. Run the simulation through every page transition for one hour. Touch via the mouse, not the touch driver.

If the PC runtime freezes on the same transition, the project is the fault and the panel can be ruled out. If the PC runtime is clean, the panel is the fault. This method is the standard isolation technique in Siemens support notes for the MP 277/377 line and is the most efficient triage available without opening the panel enclosure.

9. Solution D — Recovery from "Image file corrupted"

1. Connect the panel to the engineering PC via Ethernet (PROFINET variant) or USB (with the appropriate ProSave cable). On PROFINET variants the default IP is 192.168.0.1, panel IP 192.168.0.2; on MPI/DP variants use the USB-PPI cable 6ES7 901-3DB30-0XA0.
2. Launch ProSave. Select the panel type MP 377. Set the connection to the actual interface in use.
3. Click "Update OS" (also called "Primary download" in older toolchains). Accept any certificate prompt.
4. Power the panel from a UPS; do not interrupt the transfer. A 15" image takes 8-15 minutes depending on connection type and image size.
5. When the OS update completes, transfer the *.hmi runtime file. Verify "Image successfully installed" appears in the ProSave log.

If the OS update aborts twice in a row on the same panel, the flash is failing. Stop and RMA — the unit is no longer serviceable in the field. Do not attempt a third update; the bootloader can be left in an inconsistent state.

10. Solution E — Discontinue Sm@rtService / Web Session

If the panel is reachable over Ethernet and the customer uses Sm@rtService for remote operation, change the close procedure:

1. In the runtime, click the operator icon and select "Logoff" before closing the browser.
2. Disable the "Auto-logon" option in Control Panel → Sm@rtService → Settings.
3. If a session is already orphaned, power-cycle the panel. The Sm@rtService daemon clears the token table only at boot.

On the network side, restrict Sm@rtService to a single VLAN and to a single engineering subnet. The MP 377 Sm@rtService has no per-user lockout, so a single orphaned browser tab can hold the panel indefinitely. Restrict by source IP at the managed switch and disable the HTTP port on the customer-facing firewall.

11. Memory and Performance Reference

12. PLC-Side Diagnostics

The panel freeze is sometimes the symptom and the PLC is the cause. The S7-300 313C-2 DP used in the field case is a relatively slow CPU by modern standards; if the panel is hitting it with 200 tags at a 1 s cycle, the PLC scan can stretch beyond the watchdog tolerance and the MPI link timeouts. From STEP 7, open the diagnostic buffer of the CPU (PLC → Diagnostic buffer). Look for:

• "Communication error to partner" entries with the panel's MPI address
• Scan time warning OB80 entries
• Stop events immediately after the panel freeze timestamp

If any are present, increase the MPI baud from 187.5 kbit/s to 1.5 Mbit/s (requires all bus nodes to be rated for it) or move the connection to PROFINET on the -2AD panel variant. Monitor the OB1 cycle with a one-shot timer block; if the scan exceeds 50 ms during a page transition, the panel is waiting for tags and the freeze is downstream of the runtime, not in the runtime itself.

13. Migration to TIA Portal as a Side Path

WinCC Flexible 2007 HF4 is in the late stage of its product life. If the freeze cannot be cleared within two engineering cycles, consider migrating the project to TIA Portal and running it on a Comfort Panel (e.g. TP1500 Comfort, 6AV2 124-1QC02-0AX0) as a drop-in replacement. The conversion wizard preserves the tag list, alarms, and most scripts. Note that "Change Value" event-driven scripts in WinCC Flexible 2007 are converted to scheduled tasks or PLC-driven tags in TIA Portal; this is often the correct outcome for a project that has outgrown WinCC Flexible 2007's runtime architecture. TIA Portal project files are not backward compatible to WinCC Flexible 2007; keep a copy of the original *.hmi in archive.

14. Verification Checklist

15. Preventive Configuration

• Cap compiled project size to 4 MB on the 15" panel; 8 MB is the practical ceiling before page-load latency becomes user-visible. Anything above 10 MB is treated as a project-design defect.
• Audit scripts quarterly: any script that exceeds 30 lines of ST should be moved to the PLC unless it must run on the HMI for regulatory or display-rendering reasons.
• Keep ProSave on the same engineering PC as WinCC Flexible. ProSave version must match the WinCC Flexible service pack; mixing ProSave SP3 with WinCC Flexible 2007 SP4 has been documented to fail OS updates.
• Subscribe to the Siemens Product Safety and Security Advisory feed for the MP 377 firmware; Siemens has issued multiple advisories affecting the WinCE 5.0 build bundled on the unit. The relevant feed is at Siemens Security Advisories.
• Maintain a 1:1 ProSave backup per panel, stored on the engineering file server. RMA tickets are not accepted without a backup attached.
• On the customer LAN, place the MP 377 in an isolated VLAN and disable ICMP and HTTP from the corporate network. This blocks both the Sm@rtService residual-session failure mode and most external attack surface.

Frequently Asked Questions