Replacing a SINAMICS S120 CU320 Control Unit: Version G to Version H

The SINAMICS S120 drive platform from Siemens uses the CU320 (Control Unit 320) as its central motion and drive controller. Over the lifecycle of a machine, control units must be replaced due to hardware failure, lightning damage, firmware migration, or stocking of newer revision spares. This article documents the field-proven procedure for swapping a CU320 version G (MLFB 6SL3040-0MA00-0AA1, serial prefix S T-A52003446) with a version H unit (same MLFB, serial prefix S T-F66168255), based on the official SINAMICS S120 Manual – Control Units and Additional Components (GH1) and field experience.

1. CU320 Hardware and Firmware Background

The CU320 is a multi-axis controller that processes setpoints for up to 6 servo axes or 12 vector axes. It communicates with power modules, motors, encoders, and I/O via DRIVE-CLiQ, the proprietary real-time interface used across the SINAMICS family.

Per the SINAMICS S120 Control Units manual (GH1), the hardware revisions G and H are functionally equivalent. The revision letter on the rating plate reflects minor component changes (such as FPGA revisions or memory density updates) but does not require firmware re-flashing or parameter migration when used as a direct replacement.

2. Prerequisites

1. Back up the project: Upload the drive configuration from the old CU320 using STARTER (≤ V5.x) or Startdrive in TIA Portal (V15 and later). Save the archive (*.dsf / *.dsz / *.par) to an external PC.
2. Back up the CompactFlash card: Use a commercial CompactFlash reader and create a binary image of the original card. Verify the image hash before proceeding.
3. Document the DRIVE-CLiQ topology: Photograph or sketch the cable connections at ports 0 through 7, label every motor and encoder cable, and note the order of any cross-link between two CU320s (typical for parallel or line-module-redundant configurations).
4. Verify the spare unit is revision H: The rating plate (on the front face of the CU320, behind the CF slot cover) must show the letter H in the hardware-revision field. Confirm the MLFB matches: 6SL3040-0MA00-0AA1.
5. Tools required: Torx T10 screwdriver (for DRIVE-CLiQ connector strain relief), anti-static wrist strap, CompactFlash card reader, label maker, original Siemens CF card (or compatible industrial-grade card).
6. Personnel qualification: Only qualified electrical personnel familiar with IEC 60204-1 and the SINAMICS safety instructions may perform the replacement.

3. Mechanical and Electrical Removal of the Old CU320 (Version G)

1. Place the drive line-up in OFF-2 / OFF-3 safe state, then power down the line module (ALM/SLM/BLM) and the 24 V DC control supply.
2. Wait the prescribed discharge time (typically 5 minutes for ALM with active line filter; see the equipment nameplate for the line filter capacitor discharge time, which can be 5–10 minutes).
3. Verify zero voltage at the DC link with a properly rated multimeter (typically 600 V DC minimum for 400 V class / 1000 V DC for 690 V class).
4. Label and unplug all DRIVE-CLiQ cables (RJ45 type, keyed) from the CU320. Note port numbers: X100–X107 for ports 0–7.
5. Disconnect the PROFINET / PROFIBUS cables from X120 P1/P2 or X126 (depending on the CU320 variant; the DP variant uses PROFIBUS, the PN variant uses PROFINET).
6. Disconnect the 24 V DC supply at X124 (terminal block, two pins, 24 V / 0 V).
7. If an Advanced Operator Panel (AOP30) is connected at

   X500 or via the dedicated cable harness, unplug and label it.

8. Press the four captive latches (top and bottom of the unit) and pull the CU320 straight off the backplane. Do not pry. Avoid touching the connector pins on the rear.
9. Place the old unit on a clean, ESD-safe mat. Do not place on metal surfaces while the CompactFlash card is still inserted.

4. CompactFlash Card Migration

The CompactFlash (CF) card contains the firmware, the parameter set, and (optionally) the AOP30 project. For a version G → H swap, the original CF card must be transferred to the new unit.

1. Eject the CF card from the old CU320 by pressing the eject button. The slot is on the top face, behind a hinged cover.
2. Insert the CF card into the new version H CU320. The card must seat with the label facing the front of the unit.
3. Verify the card is fully inserted — the eject button must be flush.

5. Mechanical Installation of the New CU320 (Version H)

1. Inspect the rear connector of the new unit for bent pins or contamination. Clean with ESD-safe compressed air if required.
2. Align the new CU320 on the backplane mounting plate and press it home until the four latches engage with a distinct click. The unit must sit flush against the backplane.
3. Reconnect DRIVE-CLiQ cables in the documented order: ports 0 → 7 as recorded in step 3.4.
4. Reconnect PROFINET / PROFIBUS to the original sockets (X120 P1/P2 or X126).
5. Reconnect the 24 V DC supply at X124. Observe polarity: pin 1 = 24 V, pin 2 = 0 V. The unit's READY LED should illuminate green within a few seconds of power-up.
6. Reconnect the AOP30 if present.

6. Initial Power-Up Behavior and Known AOP Messages

On the first power-up of the new CU320 with the old CF card installed, the drive will read the topology from the CF card and re-identify the DRIVE-CLiQ nodes. This is normal and typically takes 10 to 30 seconds for a small axis count, longer for multi-axis cabinets.

Some users have observed the following AOP30 messages on the very first power-up after a CU320 swap:

7. The Double Power-Cycle Procedure

Field experience (and the SINAMICS S120 Control Units manual) confirms that the first power-up after a hardware revision swap may leave residual state in the AOP30 or in non-volatile RAM. The remedy is straightforward:

1. Power up the new CU320 once and let the boot complete. Note any AOP30 message.
2. Power down completely: switch off the 24 V supply to the CU320 and wait at least 10 seconds.
3. Power up a second time. The drive should boot cleanly with no Control unit version G message and no topology comparison errors.

This double power-cycle is required because on the first power-up, the new CU320's non-volatile fault buffer and AOP30 display cache contain the old hardware signature. The CU320 only re-writes this signature on the subsequent boot once the live check has confirmed the new unit is healthy.

8. Parameter Verification After Swap

Because version G and version H are functionally identical, no parameter changes are required. However, the following sanity checks are recommended:

To read the actual hardware revision stored in the unit, navigate in STARTER/Startdrive to Drive → Commissioning → Device Identification or read parameter r3925[0] (firmware version) and r3927[0] (firmware version internal) and the device trace under Target hardware.

9. Functional Verification

1. Visual checks: All DRIVE-CLiQ LEDs (green steady = OK, red = fault). Status LED of the CU320: green steady = Ready; green flashing 0.5 Hz = Commissioning; red = Fault.
2. Topology check: In STARTER, open the DRIVE-CLiQ topology view and confirm every node shows a green status. Cross-check the serial numbers of the connected Motor Modules and encoders against the documentation.
3. Reference signal check: Run the drive in no-load jog mode (enable pulse, jog at low speed, e.g., 50 rpm) for each axis. Verify direction of rotation, current draw, and absence of F30001 (overcurrent) or F07900 (motor speed too high).
4. Fieldbus check: Confirm the controller is in RUN, the PROFINET/PROFIBUS watchdog is not tripping, and the cyclic I/O is updating (visible in the AOP30 menu Diagnostics → Bus).
5. Safety check: Validate STO (Safe Torque Off) and SS1 if used: trigger the safety input, confirm the drive goes to STO state, and check for fault F01611 (SI: defect in a monitoring channel) – it must NOT appear; instead, the drive should report a normal stop.
6. Backup the new state: Upload the current project from the new CU320 to STARTER/Startdrive. Save the archive to a versioned folder such as Backup_YYYY-MM-DD_CU320_H_SN_T-F66168255.

10. Troubleshooting Matrix

11. When to Update the Firmware on the New Unit

You should update the firmware on the new CU320 only if:

• The spare part was stored for a long time and the original CF card firmware is older than what is required for the latest STARTER/Startdrive project.
• A new functional module (for example, safety integrated Extended Functions V2.0) requires a newer firmware base than what is currently on the CF card.
• You are migrating from SINAMICS V4.x to V5.x to support TIA Portal features.

Firmware update is done via STARTER/Startdrive over Ethernet (the CU320 has a service interface X127 at a fixed IP 169.254.11.22). The procedure is documented in the SINAMICS S120 Control Units manual (GH1) and the SINAMICS firmware update chapter of the S120 Function Manual.

12. Spare-Part Strategy and Stocking Recommendations

Because G and H are drop-in compatible, plant stockrooms can safely hold version H spares for use as replacements for older G units. The following practice is recommended:

• Store CF cards with at least the firmware version currently used in the plant, to avoid firmware mismatch on first install.
• Periodically (every 12 months) power up the spare CU320 H on a test bench and verify the CF card boots cleanly, to avoid discovering a discharged card at the moment of need.
• Label the spare with a sticker showing the last bench-test date, the firmware version, and the inventory owner.
• Keep the original shipping ESD bag and foam insert – the CF card is sensitive to ESD and mechanical shock.

13. Common Misconceptions

• "Version H is a different firmware branch." – Incorrect. The hardware revision letter is independent of the firmware version. The firmware version is a number (e.g., V4.4, V4.5, V5.1) and is reported via parameter r0018.
• "After a swap, all parameters must be re-commissioned." – Incorrect when transferring the CF card. The CF card contains the entire parameter set, and the drive will boot with the same configuration as the old unit.
• "An AOP30 message on first power-up means the swap failed." – Usually incorrect. The double power-cycle procedure resolves the AOP display cache and the drive operates normally on the second boot.
• "You can hot-swap the CF card." – Incorrect. Always remove power before removing or inserting the CF card.

14. Verification Checklist

• ☐ Old CU320 G safely removed, ESD-bagged, and labelled with location and date.
• ☐ New CU320 H rating plate shows MLFB 6SL3040-0MA00-0AA1 and revision H.
• ☐ CompactFlash card transferred without damage to the eject mechanism or pins.
• ☐ All DRIVE-CLiQ cables reconnected in the documented order.
• ☐ 24 V supply reconnected; RDY LED green steady within 30 s of first power-up.
• ☐ AOP30 cleared after second power-cycle.
• ☐ Topology view in STARTER/Startdrive shows all nodes green.
• ☐ Reference signal check (no-load jog) passed for every axis.
• ☐ Safety functions (STO/SS1) validated.
• ☐ Project backup uploaded and stored with date, serial number, and engineer name.

FAQ