Troubleshooting Siemens SINUMERIK NCU 573.5 Flash Code 1-0-9

Problem Overview

The Siemens SINUMERIK 840D sl NCU 573.5 uses a two-digit 7-segment LED display on its front bezel to report boot status and fault codes when the HMI/TCU is unavailable, corrupted, or not yet initialized. During power-up the operator observes the following sequence:

1. LED indicator 2 illuminates (NCU firmware bootloader stage 2 — hardware initialization active).
2. Display goes blank momentarily.
3. Numeric codes 1, 0, and 9 cycle repeatedly in roughly 1-second intervals (1 → 0 → 9 → 1 → 0 → 9 …).

This cycling pattern is not a normal boot progress indicator. It is a multi-state POST (Power-On Self-Test) failure that the NCU firmware is unable to clear. The control never reaches the state where it hands off to the PCMCIA-resident SINUMERIK system software, and the HMI remains dark.

The combination 1-0-9 is specifically diagnostic of a storage subsystem fault affecting either the volatile DRAM, the battery-backed SRAM, or the firmware's ability to validate the contents of its boot header.

NCU 573.5 Hardware Architecture

The NCU 573.5 is a modular controller in the SINUMERIK 840D sl product family. The relevant subsystems for the 1-0-9 fault are:

The NCU 573.5 fanless chassis accepts a replaceable PCMCIA card on the front face. The boot ROM first verifies the card, then loads the NCK, PLC, and HMI partitions into DRAM. Codes 1, 0, and 9 represent three independent failure points on this boot path. Their sequential appearance confirms the firmware is running its retry loop against a fundamentally unreliable storage layer.

7-Segment Flash Code Definitions

The three digits encountered in the 1-0-9 cycle correspond to specific fault conditions decoded by the NCU bootloader:

The cycling behavior indicates that after each individual failure the firmware attempts to re-run the entire POST sequence. Because three separate integrity checks fail in turn, the root cause must affect the common dependency of all three: typically the power supply, the PCMCIA card image, or the NCU mainboard itself.

Root Cause Analysis

The most frequently confirmed root causes, in descending order of probability for this specific code combination:

1. Defective Internal Power Supply (Most Common)

The NCU 573.5 PSU is the single highest failure component. Aged electrolytic capacitors lose capacitance, increasing ripple on the 3.3 VDC rail that feeds DRAM and the PCMCIA controller. When ripple exceeds the memory controller's tolerance, the bootloader:

• Reads corrupted data from the PCMCIA card → checksum mismatch (code 1)
• Miscompares bytes during staged PLC load → incorrect value (code 0)
• Triggers DRAM/SRAM parity/ECC errors during POST → memory test failure (code 9)

This explains why all three codes appear in sequence. A failing PSU creates all three symptoms simultaneously.

2. Corrupted or Incompatible PCMCIA System Software Card

The system software card (typically a 512 MB or larger CF card in PCMCIA adapter, Siemens part numbers in the 6FC5253-0AExx-xAAx family) must contain a header that matches the NCU 573.5 firmware version. Causes of header failure:

• Card write-protected switch engaged
• File system corruption (FAT16/32 mismatch)
• Mismatched software version (e.g., SW 4.5 card in a NCU 4.7)
• Physical damage to card contacts or slot

3. Failed PLC Submodule

The integrated PLC 317-2DP-style submodule sits on the NCU mainboard. If the submodule's flash memory or its data RAM has failed, the staged loader returns the "incorrect value" condition (code 0). This is rarely seen on a brand-new NCU but is common on units with >10 years of continuous service.

4. NC COM Module / X106 Socket Failure

The X106 connector on the NCU backplane carries the NC ↔ PLC ↔ drive communication link. Bent pins, oxidation, or a damaged NC COM module plug produce handshake errors that the bootloader classifies as code 0.

5. Battery Exhausted SRAM

The lithium battery on the NCU retains SRAM during power-off. An exhausted battery does not directly cause codes 1, 0, or 9 during POST, but combined with a marginal PSU it can produce intermittent failures that masquerade as 1-0-9.

Diagnostic Procedure

Follow the steps in order. Do not skip a step; each one eliminates or confirms a root cause.

1. Power-cycle and observe: Remove power for at least 30 seconds. Re-apply. Note whether the 1-0-9 cycle is identical and whether the LED "2" appears first. An identical fault on a fresh power-up rules out a transient.
2. Inspect the PCMCIA card: Remove the card. Inspect the gold contacts for oxidation (clean with isopropyl alcohol and a lint-free swab if needed). Confirm the write-protect switch is in the correct position. Re-seat firmly.
3. Substitute the PCMCIA card: Use a known-good card with a verified SINUMERIK system software image that matches the NCU firmware version. If the cycle clears, the original card is the fault.
4. Check the lithium battery: Measure battery voltage at the NCU battery holder with the NCU powered off. Nominal: 3.0–3.6 VDC. Replace if < 2.8 VDC.
5. Measure the PSU rails: With the NCU powered and the front cover removed, measure at the test points on the NCU mainboard:
   • +5 VDC ±5%
   • +3.3 VDC ±5%
   • +15 VDC / -15 VDC ±10%
   • Ripple on 3.3 VDC < 50 mV peak-to-peak
   Out-of-tolerance rail or excessive ripple on 3.3 VDC confirms the PSU.
6. Perform an NCK general reset: Turn the NCU rotary switch to position "1" (general reset), power on, wait 30 seconds, return the switch to position "0," and power-cycle. If the cycle persists, the firmware cannot reach the reset handler — a strong indicator of hardware failure.
7. Inspect X106 and PLC submodule: Reseat the PLC submodule and the NC COM module. Inspect X106 pins under magnification. Clean with contact cleaner if oxidation is present.
8. Substitute the NCU: As a final test, replace the NCU 573.5 with a known-good unit using the same PCMCIA card. If the substitute boots, the original NCU mainboard is faulty.

Power Supply Verification Detail

Because the PSU is the single most common cause, document the rail measurements precisely:

Use an oscilloscope, not a multimeter, for ripple. Set the bandwidth limit to 20 MHz. The 3.3 VDC rail is the most critical: any ripple above 50 mV peak-to-peak will corrupt DRAM refresh cycles.

PCMCIA Card Verification and Re-imaging

To re-image a suspect system software card:

1. Back up any machine-specific data and PLC projects using WinSCP or the SINUMERIK HMI backup function while the card is still readable, if possible.
2. Format the CF card with FAT16 (for cards ≤2 GB) or FAT32 (for >2 GB) using a PC card reader.
3. Copy the contents of the Siemens SINUMERIK system software delivery (folder structure /siemens, /addon, /oem, /user) to the card root.
4. Verify the card\siemens\sinumerik\hmi\version\mmc.ini (or equivalent) file is present and readable.
5. Lock the card with the write-protect switch before inserting into the NCU.

NCU Module Replacement Procedure

If the diagnostic procedure localizes the fault to the NCU mainboard itself (steps 1–7 above all pass, but the fault persists on a known-good card and PSU), replace the NCU 573.5:

1. Back up machine data, tool offsets, and PLC program via HMI/PC access. If the HMI is unavailable, data cannot be recovered.
2. Power down the cabinet. Lock out the main disconnect.
3. Wait 5 minutes for the DC bus to discharge.
4. Remove the NCU from the backplane by loosening the four mounting screws.
5. Label and disconnect all plug-in connectors (X106, X122, X124, drive bus, etc.).
6. Transfer the PCMCIA system software card to the replacement NCU.
7. Install the replacement NCU. Torque the screws to the Siemens specification (typically 0.8 Nm).
8. Reconnect all connectors. Verify X106 pin seating.
9. Power on. The replacement NCU should show the normal boot sequence 1 → 2 → 3 → 5 → 6 → 7 → 8 → "00."
10. Restore machine data and PLC program from backup.
11. Run axis referencing and a complete machine acceptance test before returning to production.

Repair vs. Replace Decision Matrix

Field experience indicates that NCU mainboard-level repair of the 1-0-9 condition yields successful restoration in roughly 10% of cases because the root cause frequently traces to multiple aged components rather than a single failed part. NCU swap with a refurbished replacement unit is the standard service procedure.

Verification After Repair

After any corrective action, perform the following verification before returning the machine to production:

1. Boot sequence check: Confirm the 7-segment display progresses through the normal sequence and stops at "00." within 60 seconds of power-on.
2. HMI check: Confirm the operator HMI displays the channel status, axis positions, and alarms list without error indicators.
3. PLC online check: Connect to the PLC via STEP 7 and confirm online status with no diagnostic buffer entries.
4. Drive bus check: Confirm all drives report "RUN" state on the HMI drive diagnostic screen.
5. Axis referencing: Run a complete reference-point traverse on every NC axis.
6. Test program: Execute a known-good part program in single-block with reduced rapid override to confirm motion, spindle, and tool-change functionality.
7. Alarm log: Clear the alarm history and confirm no new alarms are logged after 30 minutes of operation.

Preventive Recommendations

• Replace the NCU lithium battery every 12 months regardless of measured voltage.
• Maintain cabinet ambient temperature below 35 °C. The PSU capacitor lifetime halves for every 10 °C increase above its rated operating temperature.
• Perform a controlled shutdown rather than a hard power cut whenever possible.
• Keep a verified backup PCMCIA card and a current NCU backup image offline.
• Log the 7-segment display state at every planned maintenance outage for trend analysis.

Related Boot-Time 7-Segment Codes

For context, the other NCU 573.5 boot codes you may encounter and their meanings: