Sinumerik 840D PCU20.ABB Loading: HMI Embedded Restore

Problem Overview: HMI Embedded Boot Hang on SINUMERIK 840D

The SINUMERIK 840D operator panel can become stranded on the splash logo with the message HMI embedded version 06.02.42 and a secondary line reading waiting for PLC connection or, after the underlying communications path is disturbed, waiting for NCK connection. The control does not advance to the operator menu, and once it does, a set of non-resettable alarms (2001, 120.008, 101000) is present in the diagnosis screen. In many cases the same panel is also reported with a cmos battery fail on cold start. This document describes how to bring the panel back online by reloading the HMI Embedded image, performing a general reset of the NCK and PLC, and reloading the NC.ARC / PLC.ARC project backups.

The procedure targets two hardware variants in particular:

• PCU20, order number 6FC5210-0DF00-0AA1 (SPC 166 MHz / 32 MB / DC 24 V)
• PCU20, order number 6FC5210-0DF00-1AA3 (used in shop-turn / similar configurations downgraded to HMI Embedded V06.04.60)

Both panels accept a single, fixed flash-image file name — PCU_20.ABB — copied to a Compact Flash Card or PCMCIA memory card formatted as FAT16. The file is then activated through the PCU20 service menu, not through SIMATIC STEP 7 or through the NCK file utilities.

Affected Hardware Identification

Before any re-imaging is started, confirm the part number stamped on the back of the operator panel, the HMI version reported on the splash screen, and the NCU module installed in the cabinet. The HMI boot string HMI embedded version 06.02.42 identifies HMI Embedded V06.02 SP5 HF42 software. The image PCU_20.ABB is matched to a particular service pack and is not interchangeable between major releases (e.g. an image built for V06.04.60 cannot be downgraded onto a panel that shipped with V06.02.x without following the documented downgrade procedure).

Replace the panel spare with the exact part number stamped on the failed unit. Loading a PCU_50.ABB onto a PCU20 is not supported; the boot loader refuses the wrong image and reverts to the previous screen, which is one cause of a loop where the operator believes the load has failed.

Failure Symptoms and Alarm Code Mapping

Three alarms are typically active simultaneously when the operator panel cannot reach the PLC, plus one or more NCK-side alarms when the underlying fieldbus is missing. The numeric IDs map as follows:

Note the diagnostic transition: when the technician tested the system with the X101 cable unplugged, the HMI changed from waiting for PLC connection to waiting for NCK connection. The HMI always reports the lowest layer that has not yet answered. A failure to see either the PLC or the NCK through the same X101 cable is therefore strong evidence that the HMI itself is healthy but the underlying NCU/PLC is not — and the right first action is to recover the NCU and PLC, not to chase a HMI image problem.

NCU Status Display and LED Diagnostics

The NCU module exposes a seven-segment display and a row of LEDs. During normal run-up the segment cycles through 1, 2, 3, 4, 5 and finally settles on 6. With the PLC in STOP the segment shows a small c with the decimal point lit (often rendered as c.) for several seconds before falling back to 6. This is the standard indication that the PLC firmware has been loaded but is not executing the cyclic OB1.

Figure 1 — NCU seven-segment run-up sequence (1 → 2 → 3 → 4 → 5 → 6). A persistent c. between 5 and 6 indicates PLC STOP.

The LED pattern reported in the failure case is:

Confirm the same pattern with the X101 cable inserted and removed. In the case described, the segment and LEDs were identical with and without the cable, which rules out a cable break and points to the PLC firmware not having been loaded correctly.

Root Cause Analysis

Four candidate root causes have to be considered when the panel shows the V06.02.42 splash and then hangs for 35–50 minutes before presenting the operator menu:

1. PLC project not loaded or CRC corrupt. The PLC-CPU is in STOP with PF (periphery fault). The HMI retries the connection and eventually times out, surfacing alarms 2001, 120.008 and 101000.
2. NCK project (NC.ARC) not loaded. When the panel sees no NCK at all on the bus, it switches the wait message from PLC to NCK. This is the exact behaviour reported after the technician disturbed the NCK file load at 50%.
3. PCU20 flash image corrupt or out of revision. A failed upgrade leaves the panel on the splash but the underlying NCU and PLC are not at fault. In this case the menu usually appears, but the panel crashes back to splash after a few minutes.
4. Hardware fault on the panel or X101 cable. With the cable removed, the panel must say waiting for NCK. If the panel stays on splash without changing the wait text, the panel itself is suspect.

The reported sequence — panel eventually shows the menu, technician performs a general reset, then the PLC file load stops at 50%, the wait message changes from PLC to NCK after the disturbance, and the PLC PS/PF LEDs indicate STOP — is consistent with root cause (1) plus (2): the PLC project did not complete its load, and the disturbance left the NCK link unstable. The PCU_20.ABB image itself is not necessarily damaged; the focus must be on the NCK and PLC restore.

Preparing the PCU_20.ABB Restore Media

The PCU20 boots its flash image from a removable card inserted into the PCMCIA slot. The card must satisfy the following constraints:

• FAT16 (FAT16B) file system. FAT32 is not recognised by the PCU20 boot loader.
• File placed in the root directory of the card.
• Filename must be exactly PCU_20.ABB (uppercase, with the underscore between PCU and 20 and the literal extension .ABB).
• If a custom user ramp-up screen is required, the bitmap must be named LOGO_OEM.BMP and placed in the same root directory.

On a Windows host, prepare the card as follows:

1. Insert a Type II PCMCIA Compact Flash card (or a PCMCIA adapter holding a CF card) into the laptop.
2. Open Disk Management, delete any existing partition, create a new primary partition and format it as FAT (not FAT32, not exFAT, not NTFS). Use a default allocation unit size.
3. Assign a drive letter and copy the supplied PCU_20.ABB image to the root of the card.
4. If a custom splash is required, copy LOGO_OEM.BMP (24-bit or 8-bit BMP, 640×480 typical) to the same root.
5. Safely eject the card from the host.

On a Linux host, the equivalent sequence is:

# Identify the device (do NOT pick /dev/sda)
lsblk

# Wipe and create a FAT16 partition
sudo dd if=/dev/zero of=/dev/sdX bs=1M count=1
sudo fdisk /dev/sdX
  # create a new primary partition, type 6 (FAT16), write

# Format and label
sudo mkfs.fat -F 16 -n PCU20IMG /dev/sdX1

# Mount and copy
sudo mount /dev/sdX1 /mnt/pcu20
sudo cp /path/to/PCU_20.ABB /mnt/pcu20/
sudo umount /mnt/pcu20

Loading the PCU_20.ABB File via the PCU20 Service Menu

The restore of the HMI image is performed entirely from the PCU20 service menu — there is no involvement of STEP 7, SIMATIC Manager, or TIA Portal for the panel image. The procedure is:

1. Power down the SINUMERIK 840D at the main disconnect and wait for the NCU seven-segment display to extinguish.
2. Insert the prepared PCMCIA card with PCU_20.ABB into the PCU20 PCMCIA slot on the rear of the panel.
3. Power the control back on. The PCU20 firmware reads the card during POST and presents the Service Menu instead of the normal splash, because it detects a valid PCU_20.ABB on the card.
4. Select Update / Install HMI Software and confirm the source is the PCMCIA card. The system copies PCU_20.ABB into the internal flash, verifies the CRC and reboots.
5. When the PCU20 reboots, the splash returns with the new HMI Embedded version string (e.g. HMI embedded version 06.05.49). Remove the PCMCIA card only after the panel has reached the operator menu.

For the shop-turn downgrade case (panel 6FC5210-0DF00-1AA3) the procedure is identical except the image on the card is built for V06.04.60; the official Siemens support document describes the downgrade path and the expected PCU_20.ABB version.

General Reset of NCK and PLC Using the S3 and S4 Rotary Switches

If the HMI image is correct but the NCK and PLC are still in an undefined state, perform a general reset on the NCU module using the S3 and S4 rotary switches before reloading the archive files. The procedure clears the SRAM of the NCK and the PLC, returning the control to factory defaults.

1. Power the control off.
2. Set S3 = 1 (NCK general reset) and S4 = 1 (PLC general reset) on the NCU module.
3. Power the control on. Wait until the seven-segment display cycles 1 → 5 → c. → 6, then power off again (typically 30–60 s).
4. Return S3 and S4 to position 0.
5. Power the control on again. Both subsystems are now in factory state with default machine data and an empty PLC project.

Restoring the NC.ARC and PLC.ARC Backups

Once the NCK and PLC are in a clean state, load the project archives:

1. Copy NC.ARC and to a PCMCIA card (FAT16, root directory). The card can be the same one used for the HMI image, but the PCU_20.ABB file must be removed first — the boot loader will trigger an unwanted HMI upgrade otherwise.
2. Insert the card into the NCU PCMCIA slot (not the PCU20 slot).
3. From the HMI operator menu, navigate to Commissioning → NC → NC Card / Backup Restore and select NC.ARC. The NCK accepts the archive and reboots.
4. After the NCK reboot, navigate to Commissioning → PLC → PLC Card / Backup Restore and select PLC.ARC. The PLC transitions from STOP to RUN. The PS LED should now be steady green and the PF LED should extinguish.

If the PLC still shows PF and the load stops at 50%, the CRC of the archive is wrong. Re-export PLC.ARC from the SIMATIC STEP 7 project on the engineering station, ensuring that the offline/online consistency is correct, and repeat the load.

X101 MPI Cable and PLC Connection Verification

The X101 cable carries the MPI bus between the PCU20 and the NCU. The cable also provides the keyboard line on certain hardware revisions. A damaged X101 cable is the most common reason for the panel to oscillate between waiting for PLC and waiting for NCK messages.

Verify the cable with a multimeter on continuity and on the +5 V / P24 rails (pins 6, 7). A reading of 0 V on pin 6 with the panel powered indicates a torn power line and will keep the MPI termination inactive. The MPI bus is RS-485 and must be terminated at both ends — typically 220 Ω between pins 3 and 8 inside the connector hoods.

Use STEP 7 with an MPI/PC adapter on a tap to read the bus topology: if STEP 7 sees the NCU and the PLC but not the PCU20, the panel side of the cable is open. If STEP 7 sees the PCU20 but neither the NCU nor the PLC, the cabinet-side wiring is open or the NCU is not powering its MPI transceiver.

Drive Ready Signal and Cross-Reference Checks

Once the NCK and PLC are in RUN, the next gate is the drive-ready chain. The PLC evaluates the drive ready signal on connector X111 of the NCU; the signal is sourced from the SIMODRIVE 611D power section. A missing drive-ready signal blocks all axis enable and surfaces alarm 63, 64 or 48 depending on the firmware release.

The diagnostics flow is:

1. With the PLC in RUN, monitor the input byte for the drive-ready bit in the STEP 7 online view.
2. With the main contactor energised but no enable, the bit must read 1 (ready). If 0, check the 611D bus modules, the I/R module and the X111 wiring.
3. Confirm the drive bus (Profibus to the 611D modules) is alive — the green LEDs on the SIMODRIVE modules must be steady.

The Siemens doconweb documentation set for SIMODRIVE 611D (release 04.2010) is the authoritative reference for the X111 pin-out and the drive-ready signal timing.

CMOS Battery, PCU20 Variants and Long-Term Reliability

The cmos battery fail message that can appear on a cold start of the PCU20 originates from the on-board lithium cell that backs the RTC and BIOS settings. The cell is service-replaceable on the PCU50 family; on the PCU20 the cell is soldered and the panel is not designed to be opened in the field. A persistent battery-fail message after a clean HMI reload is therefore an indicator that the panel itself is at end-of-life, and the correct field action is to replace the panel, not to attempt a battery swap.

Send the failed panel to a Siemens-authorised repair centre. Continued operation with a depleted cell causes the panel to revert to default BIOS settings on every power-down, which in turn can corrupt the HMI boot environment.

Verification Procedure After Restore

After the HMI image is reloaded, the NCK and PLC are reset and the archives reloaded, run the following verification before handing the machine back to production:

1. Power the control off and back on. Confirm the splash reports the expected HMI version and that the operator menu appears within 60 s (not 35–50 minutes).
2. From the diagnosis screen, confirm that alarms 2001, 120.008 and 101000 are no longer present.
3. NCU seven-segment display: must cycle 1 → 6 and remain at 6 without the c. indication.
4. PLC LEDs: PS green steady, PF off. Watch the PLC for at least 60 s to confirm the cyclic OB1 is executing without stop events.
5. Drive-ready: input bit high, no alarm 63/64/48.
6. Jog one axis in each direction in setup mode and confirm the actual position tracks the commanded position on the HMI.
7. Run a full reference-point traverse to confirm encoder calibration has been preserved across the reset.

If any of the above fails, return to the corresponding section of this document and re-run the procedure; do not clear alarms until the underlying subsystem is in RUN.

FAQ