SINUMERIK 840D sl NCU 710 CF Card Backup via Service Shell

Problem Overview

On a SINUMERIK 840D sl system configured with an NCU 710 numerical control unit and a separate PCU 50.3 industrial PC, technicians performing a CompactFlash (CF) card backup frequently encounter the following symptom: inserting the NC bootable USB stick into the NCU 710 and powering the rack does not produce the familiar Service Center / eboot screen on the connected Thin Client Unit (TCU). Instead, the system boots normally and the HMI (HMI Operate) appears as if no service stick had been inserted.

The same procedure works perfectly on a TCU-only configuration (no PCU attached), which confirms the boot stick itself is functional. The root cause is an HMI display routing conflict between the NCU's internal HMI and the PCU 50.3's HMI Operate runtime: only one HMI may own the active display channel at any given time.

This reference documents the three field-proven workarounds, the underlying X120/X127 addressing, the seven-segment boot indicator states, and the .tgz image capture workflow for 8 GB NCU CompactFlash cards.

Affected Components and Firmware

Root Cause: HMI Display Routing

The 840D sl architecture permits both the NCU's embedded HMI and the PCU's HMI Operate to serve as the active HMI host. By default, the system hands the TCU display to whichever host responds first to the DHCP request on the service network (X127) or the plant network (X120). When the PCU 50.3 is present and powered, its HMI Operate runtime typically claims the display before the NCU's internal Service Center has a chance to surface the eboot menu.

Two addressing ranges must be kept separate:

Symptom confirmation: if the PCU's network adapter has been reconfigured to a different subnet or its HMI service has been disabled, the NCU boot stick displays the eboot screen normally. The moment the PCU 50.3 HMI comes back online, it preempts the NCU display.

Prerequisites

1. A bootable NC service USB stick prepared with the SINUMERIK Service Center image matching the NCU firmware line (V4.x). Verify the stick on a TCU-only machine first to confirm it boots to the eboot menu.
2. A Windows service laptop with the following tools installed:
• VNC Viewer (RealVNC, TightVNC, or TigerVNC) — connect to port 5900 of the NCU.
• WinSCP or any SCP/SFTP client — used to drop a script that toggles the NCU internal HMI.
• PuTTY or any SSH client — for the "enable hmi" / "disable hmi" shell command.
• A network cable (CAT5e or better) and access to either the X127 or X120 port on the NCU 710.
3. If the 8 GB CF card is to be backed up to a network share (recommended on Windows), the target share must be formatted as NTFS. FAT32 will refuse files larger than 4 GB and the image will silently fail partway through. This requirement is documented in Siemens Support entry 56733508 — SINUMERIK 840D sl: Backup / Restore of the 8 GB NCU CompactFlash card.
4. At least 12 GB free space on the destination drive to accommodate the compressed .tgz archive (the on-disk image is roughly 6-8 GB after compression).

Method 1 — VNC into the NCU Service Shell (Recommended)

This is the cleanest method because it does not require re-routing the active HMI and it does not risk leaving the PCU 50.3 in a non-default state.

1. Insert the NC service USB stick into any of the USB ports on the NCU 710 (front-panel USB-A is preferred).
2. Power-cycle the NCU (24 V OFF / ON) or trigger a controlled restart from the operator panel.
3. Watch the seven-segment display on the NCU front panel during boot. The expected sequence is:

4. Connect the service laptop directly to the X127 port of the NCU using a point-to-point cable (no switch required when the laptop is set to 192.168.215.2 / 255.255.255.0). Alternative: connect to X120 with the laptop at 192.168.214.2 / 255.255.255.0 when the plant network is isolated.
5. Launch VNC Viewer and connect to 192.168.215.1:5900 (X127) or 192.168.214.1:5900 (X120). The Service Center desktop appears, identical to the one normally seen on a TCU-only system.
6. From the Service Center main menu select Backup/Restore > Backup complete CF card. Choose the destination: USB stick, local HDD (if one is mapped), or network drive. For 8 GB CF cards, use a network drive formatted as NTFS as documented in Siemens Support entry 56733508.
7. Confirm the file name (default backup_<NCU_serial>_<timestamp>.tgz) and start the backup. Expected duration on NCU 710: 18-35 minutes for an 8 GB card over gigabit Ethernet.
8. Once the Service Center displays Backup completed successfully, power down the NCU, remove the service USB stick, and reboot into normal operation.

Method 2 — Enable NCU Internal HMI via WinSCP

Use this method when the VNC path is unavailable (firewalled laptop, no DHCP, X127/X120 blocked) but WinSCP file transfer still works.

1. Connect the service laptop to X127 (or X120) and verify SSH reachability with PuTTY: ssh [email protected]. Default credentials on the NCU Linux are root / SUNRISE for older service images, or the password defined during the latest commissioning. Newer firmware prompts for password change on first login.
2. Open WinSCP with the same IP and credentials, protocol SCP.
3. Navigate to /card/user/system/configuration/ on the NCU.
4. Create or edit the file hmi.ini with the following content:

[HMI]
EnableInternalHmi=1

5. From the PuTTY shell issue the command enable hmi. The next time the NCU is rebooted with the service USB stick inserted, the TCU display will be sourced from the NCU's internal HMI, the eboot screen will appear, and the Backup/Restore menu becomes reachable.
6. Perform the backup as described in Method 1, steps 6-8.
7. After backup, return to the PuTTY shell and issue disable hmi to release the display back to the PCU 50.3. Verify by rebooting without the service stick — the HMI Operate on the PCU 50.3 should once again own the TCU display.

Method 3 — Service Center SSD Image (PCU 50.3 Alternative)

When the goal is to recover a corrupted PCU 50.3 rather than back up the NCU 710's CF card, a CF-card backup is the wrong tool. The PCU runs on an SSD/HDD with Windows, not on the NCU's CompactFlash. For PCU systems the field-proven procedure is to capture a disk image through the Service Center instead of the NCU's backup utility.

1. Attach an external USB DVD-ROM or a USB stick containing a Windows PE / Service Center image to the PCU 50.3.
2. Boot the PCU from the external media (BIOS boot order may need to be changed; on PCU 50.3 the F2 / F12 key accesses the boot menu at POST).
3. Run the disk-imaging tool (ImageX, Acronis True Image, or the Service Center disk-imaging module) and capture the entire PCU SSD to an external USB drive or a network share.
4. Restore on the replacement SSD using the same tool, then re-seat the license key (CFast card with the SINUMERIK license) on the new drive.

Boot Sequence and Seven-Segment Diagnostics

The NCU 710's two-digit seven-segment display provides a definitive indication of which subsystem owns the display. When the service stick is inserted but no TCU or PCU display responds, the blank display (segment '6' with all LEDs off) means the Service Center has loaded the internal HMI server and is waiting for a VNC client. This is the correct state and proves the boot stick is functional.

Network Drive and Storage Requirements

The 8 GB NCU CompactFlash card is backed up as a single .tgz (gzip-compressed tar) archive. On FAT32 file systems the 4 GB single-file limit truncates the archive silently. The remedy specified in Siemens Support entry 56733508 is to use a network share formatted as NTFS. Local USB media larger than 4 GB can also be used if formatted as NTFS or exFAT.

SMB / CIFS share mount syntax on the Service Center shell:

Verify the mount before launching the backup:

df -h /mnt/backup
mount | grep backup

Verification

1. After the Service Center reports Backup completed successfully, list the contents of the destination directory and confirm the file size is at least 3.5 GB and the timestamp matches the backup window.
2. Compare the SHA-256 checksum generated by the Service Center against a freshly computed checksum on the destination host:

3. Power down the NCU, remove the service USB stick, and reboot. Verify the TCU displays HMI Operate as before the backup.
4. If Method 2 was used, confirm the hmi.ini file is reverted and the disable hmi command was issued. Inspect /card/hmi/log/hmi_startup.log for the line HMI source = PCU.
5. Validate the archive by performing a dry-run restore on a bench NCU or in a virtual SINUMERIK environment before discarding any prior backup.

Troubleshooting Matrix

Field-Proven Best Practices

• Always perform the backup from the same firmware line as the running NCU software. Mixing V4.7 service sticks with V4.95 NCU cards can produce partial restores with mismatched PLC symbols.
• Document the NCU serial number and the NCK version in the backup file name. The default Service Center file name is acceptable but adds ambiguity when archiving across multiple machines.
• Keep at least three generations of backups on separate physical media. Store one off-site to recover from fire or water damage.
• Verify every backup with a dry-run restore on a test bench before deleting the previous generation. A backup that has never been restored is not a backup.
• Tag each USB stick with the firmware line, build date, and the NCU serial it was built for. Industrial environments accumulate dozens of near-identical sticks and confusion is the leading cause of wrong-firmware restores.
• For NCU 710 specifically, prefer Ethernet backup over USB backup. The CF card write bandwidth (~25 MB/s sustained) saturates a USB 2.0 stick quickly; gigabit Ethernet routinely delivers 60-90 MB/s and halves the backup window.

FAQ