Sinumerik 840D NCU 57.2 Blank D840 HMI Status 6 Recovery

Sinumerik 840D NCU 57.2 Blank D840 HMI Status 6 Recovery

1. System Overview

The reported machine is a Sinumerik 840D (powerline) control running on an NCU 57.2 (article number 6FC5357-0BB33-0AE1) with three SIMODRIVE 611 digital drives for the X, Y, and Z linear axes and an OP 840 D operator panel (6FC5210-0DA20-2AA1). The reported fault is a blank D840 HMI after power-up, a 7-segment status "6" on the NCU 57.2, and PLC indicators PF = ON and PS = flashing. After a general reset via the S4 mode selector the NCU briefly runs but reverts to the fault state when the main supply is cycled. This article walks through identifying each subsystem, interpreting the boot indicators, and executing a structured PLC / NCK / HMI / drive commissioning sequence so the control retains its state across a power cycle.

2. Component Identification

The D840 panel part number (6FC5210-0DA20-2AA1) confirms an MMC (HMI Advanced) generation panel; it expects to receive its startup screen from the NCU over Ethernet. A black, lit screen with no backlight flicker and no menu is consistent with a loss of the HMI application image on either the NCU CF or the local flash partition.

3. 7-Segment Status Codes on the NCU 57.2

The 7-segment display on the front of the NCU reports the highest-numbered outstanding alarm state. Single-digit values indicate NCK boot / readiness states; capital letters (e.g. A, B, C, E) are used for boot-mode and emergency-boot diagnostics.

A persistent "6" with a general reset that does not survive a power cycle is normally a symptom of missing or corrupt NCK startup files on the CF card rather than a hardware fault on the NCU itself.

4. LED Status on the NCU 57.2

5. Root Cause Analysis

1. The compact flash card on the NCU holds three logical partitions — /system, /user, and /addon. The /user partition hosts the machine manufacturer\'s archived NCK data, the PLC S7 project, the HMI Pro / HMI Advanced project and the drive archive.
2. If the HMI display is blank from cold start and the NCU remains on 7-segment "6", the most likely cause is a missing or unreadable CF card user partition. The fact that the value "6" persists across a power cycle confirms that the NCK is loading something but cannot commit it permanently.
3. The general reset sequence (S4 to position 3, cycle power, S4 to 0) forces NCU 57.2 to wipe its retained state and repopulate it from the CF card. If the CF card is empty or formatted with a foreign image, the reset simply re-installs the missing or corrupt state on each cycle.
4. A second possibility is the OP 840 / D840 itself: if the OP has lost its loaded MMC image, the panel can light the display but stay black until its image is reinstalled through HMIRestore or via Ethernet loader.

The reported LED combination matches the more common root cause — the NCU can no longer complete NCK configuration after replacing the boot archive.

6. Commissioning Software Stack

The PG / PC must have the matching SINUMERIK toolbox installed — the SINUMERIK PLC basic program depends on FB / DB blocks that differ by firmware version. A wrong version produces a clean boot but a non-running PLC (exactly what the PS flashing indicates).

7. Hardware Connection Map

Connect a Sinumerik-equipped PG to NCU 57.2 ports X120 (PROFINET service) and X130 (PROFINET LAN), set its TCP/IP to 192.168.214.10 / 255.255.255.0 and access the NCU service menu at https://192.168.214.1 for SinuCom NCK operations.

8. Step-by-Step Recovery Procedure

Step 1 — Capture the current fault image

1. Power on at main supply. Note the 7-segment value and whether STOP / RUN / PF / PS LEDs are lit. Photograph them.
2. From a PG with STEP 7 + SIMATIC Manager, select PLC → Operate / Download / Module Information → Diagnostic Buffer on PROFIBUS DP / Ethernet. Capture the last 20 entries — they identify whether the PLC was waiting for NCK or for a missing DB.
3. If the NCU 7-segment reads B, C, E or any alphanumeric, follow the boot / emergency-boot path before proceeding.

Step 2 — Inspect the Compact Flash card

1. Power off, wait 30 s for DC-link / bus capacitor discharge. Open the CF slot cover, eject the card.
2. Mount the CF in a USB CF reader; do not run any background indexing on the host PC.
3. Inspect the partition table. A properly configured user partition is FAT32 with a add_on, user, system layout; an entry marked FREE SPACE at the head of the card indicates it was wiped.
4. Compare the directory with a known-good backup. The customer\'s machine manufacturer normally provides a .arc of the original commissioning (e.g. install_840d.arc) — copy it to /user on the CF.
5. If the original archive is unavailable, request the machine manufacturer\'s commissioning disk or derive it from SimuTrain\'s matching machine dataset.

Step 3 — Apply a machine reset via S4

1. Position 3 of S4 requests a general reset of NCU 57.2.
2. After powering on, the 7-segment will cycle through 1, 2, 3, 5, 6 while the operating data is being decompressed from CF.
3. If the cycle is interrupted before the 7-segment settles to a constant number, repeat the procedure.

Step 4 — Reload PLC user program

1. Start SIMATIC Manager, open the project that matches the machine OEM.
2. Set the access point SINUMERIK, target PC Adapter (Ethernet) with IP 192.168.214.10, subnet 255.255.255.0.
3. From PLC → Download, push the project onto the 317-2DP inside the NCU.
4. Confirm RUN goes green, PS turns off, PF remains off.

Step 5 — Configure drive references

1. Open SinuCom NCK on the PG.
2. Set the MD20050 $MC_AXCONF_GEOAX_ASSIGN_TAB and MD20070 $MC_AXCONF_MACHAX_USED entries — they must mirror the OEM cycle for X, Y, Z.
3. Activate PROFIBUS DP at address 6 (NCU is the master) and 10 / 11 / 12 for the three SIMODRIVE 611 modules.
4. Run Set Drive Reference Points under Commissioning → Drive; the drives must report RDY before proceeding.

Step 6 — Restore the HMI image on the D840

1. Use SINUMERIK HMI Advanced Loader: Start → SINUMERIK → Commissioning → Service Desktop → HMI Image Update.
2. Select the MMC image matching the panel part number — for the OP 840 (6FC5210-0DA20-2AA1) the compatible image is MMC V4.4 to V4.7 SP1 depending on NCU software ship level.
3. Transfer the image over Ethernet to the OP. The display remains blank for several minutes.
4. Once HMI running appears at power-on, the panel will pull the operator interface from the NCU.

Step 7 — Final commissioning walk-through

1. Run Commissioning → Series Commissioning in HMI to apply the OEM archive. Capture a fresh NCK + PLC backup.
2. Run a dry axis move in JOG at 10 % velocity override per axis; check direction using the reference direction flag in MD32110.
3. Activate the safety circuit and verify E-STOP via NCU safety integrated — the SF LED must NOT be lit when the E-Stop loop is closed.

9. Verification

10. Troubleshooting Matrix

11. Machine Manufacturer Relationship

The NCU 57.2 alone is not a complete control — Sinumerik-based milling and lathe machines require commissioning data generated by the machine builder (e.g. DMG, Mazak, Gildemeister) for every axis and for the interface to the safety logic and coolant / spindle drives. Two practical paths exist for an end user who has only the bare hardware:

• Request the machine manufacturer\'s complete commissioning package. This is the only supported path. Without it the NCK will boot but every axis will alarm 25201 "Axis configuration error".
• Use SinuTrain on a PC to prototype and review G-code part programs off-line; SinuTrain cannot, however, generate the OEM commissioning archive.

12. HMI Side: Configuring the Operator Panel

The D840 is a passive operator panel — there is no application code that the user has to write specifically for the HMI. The HMI runtime is delivered pre-installed on the NCU CF card; the panel pulls it on boot. Therefore the answer to the user\'s question "will I program the HMI or no?" is: only if the machine builder commissioned a custom HMI project. In the absence of an OEM project, the panel will load the basic MMC template. The menus shown under Commissioning → HMI provide:

13. PLC Programming Workflow

The PLC inside NCU 57.2 is a SIMATIC S7-300 PLC 317-2DP. The PLC controls the interface to the drives (PROFIBUS I/O), reads the NCK state, and outputs signals to the user I/O (tool changer, coolant, hydraulics, spindle enable). For a 3-axis retrofit the minimum scope is:

1. Set DB31 – DB33 assignment to correspond to X, Y, Z axes (matches NCK channel and axis mapping).
2. Implement interface blocks FB101–FB104 and the emergency stop / group fault logic per the OEM circuit diagram.
3. Set safety bits in DB1000–DB1007 — drive enable per axis, controller enable, axis enable pulse.
4. Pull the program into the NCU via PROFIBUS DP at runtime — the runtime project lives on the CF card and is reloaded by STEP 7 each boot.

14. Drive Commissioning Notes

SIMODRIVE 611 digital uses SimoCom U for parameterization. The drive objects must match the architecture set in NCK machine data.

15. Power-Cycle Validation

After completing Steps 1–7 above, perform five cold-start power cycles:

1. Switch main supply off for at least 60 s.
2. Switch on. After 90 s the 7-segment must display a consistent value (typically 6 until references are taken, then 7 after referencing).
3. Confirm PF LED stays off and PS LED remains off across all cycles.
4. Run a known short G-code program such as:
   G54 G90 G17
F500
G01 X100.0 Y50.0 Z0.0
M30
5. Capture a fresh Series Commissioning backup on a second CF card and store with the machine logbook.

16. Field-Proven Caveats

• An NCU 57.2 with a battery (article 6FC5247-0AA18-0AA0) in good condition retains PLC retentive data even with no power; without the battery OR with an exhausted battery, every power-down clears retentive flags. Confirm battery voltage each service visit.
• Always save a good backup after every commissioning step. The 840D archive format is a single .arc; keep at least one image per machine state.
• PS flashing together with PF OFF is a benign state used by NCK to tell the PLC it is not yet ready — but in the present case PF is ON, which is not normal. Diagnose PLC STOP before diagnosing the HMI.
• Do not confuse PI service (_N_SET_TIME, _N_XUSER_...) requests sent through NCK with the older /_N_... archive commands — both still appear in older manuals, but SinuCom NCK can handle either transparently.
• The D840 panel does not have user-replaceable firmware — re-imaging requires SinuComNCK HMI Service Desktop over the LAN from a PG.

17. Programming and Reference Resources

For programming background beyond hardware commissioning, the following manufacturer-tier references are recommended:

• The Sinumerik Operate Programming Manual for the G-code dialect of the specific machine (milling G-code or turning G-code varies).
• Siemens Industry Online Support articles for 6FC5357 and 6FC5210 — search the catalog for "NCU 57.2 Commissioning Manual" and the latest SINUMERIK 840D Functional Description.
• For CNC programming fundamentals (G-code, work offsets, part program structure), refer to the Autodesk CNC programming reference (CNC Programming Overview) and the Mitsubishi Electric lathe programming primer (CNC Lathe Programming Basics PDF) for a generic G-code reference; the G-code dialect itself, however, is set by the machine manufacturer\'s cycle package, not by the NCU image alone.
• Open-source documentation at the Sinumerik 840D / 840D sl manuals section of Siemens Industry Online Support provides the canonical interface definitions for the PLC basic program.

Because the NCU 57.2 ships with the SINUMERIK Operate / MMC image already loaded, an end user does not need to write code for the HMI — the HMI application is delivered with the commissioning archive. Custom HMI screens, when needed, are built with WinCC flexible / SINUMERIK HMI Advanced Designer but require an OEM project context.