SINAMICS G120 CU240E-2 STARTER Download BSOD Troubleshooting

When commissioning a SINAMICS G120 Control Unit CU240E-2 DP with STARTER V4.3 over a USB cable, the project download progresses to 94% of the progress bar, stalls for several seconds, the CU performs an internal reset, and the engineering PC enters a Windows Blue Screen of Death (BSOD). The fault is reproducible on every reconnection attempt and is not cured by unplug/replug cycles alone. This reference documents the field-verified resolution, the four-class root cause analysis, and the diagnostic sequence used to determine whether the failure is host-side (USB driver, STARTER installation, PG/PC interface), firmware-side (parameter set corruption, RAM-to-ROM mismatch), or hardware-side (damaged CU, missing Power Module supply).

1. Problem Statement and Symptom Table

The 94% threshold corresponds to the final RAM-to-ROM staging block when the "Copy RAM to ROM" option is enabled. If the CU detects a parameter set that requires a non-volatile save and the host USB stack is unable to commit the pagefile write inside the watchdog window, the CU resets and the kernel driver on the host side faults.

2. Affected Components, Order Numbers, and Firmware

Reference manuals:

• SINAMICS G120 CU240E-2 Operating Instructions
• STARTER Commissioning Tool Documentation
• SINAMICS G120 List Manual (Parameter List)

3. Root Cause Analysis

The fault is a stack mismatch between the STARTER upload protocol and the CU commissioning state machine. The 94% mark is the last public checkpoint before the final block write that triggers a parameter commit. Four contributing causes have been observed in the field, and they often stack.

3.1 Power Module not connected to the Control Unit

The CU240E-2 requires the 24 V backplane supply from the PM (or from terminals 31, 32 of an external supply) during programming. If the CU is fed only through the USB port, the 5 V logic rail is shared with the USB PHY, and any spike during the parameter commit causes a brown-out on the CU side and a corresponding over-current detection on the host USB port. Siemens Technical Support has confirmed this is the most common root cause and the first item to verify on every field incident.

3.2 USB driver instability in STARTER V4.3

STARTER V4.3 ships with the SiemensUsbDriver v1.5.0.4 stack. The stack is signed for Windows 7 and early Windows 10 builds, but the IRQL handling in the driver does not cooperate cleanly with Windows 10 20H2 and later kernels. The 94% progress window opens an extended DPC, and the host kernel raises IRQL_NOT_LESS_OR_EQUAL. A clean STARTER reinstall registers the correct SiemensUsbDriver v1.6.1.0 and resolves the host-side fault.

3.3 Copy RAM to ROM checked at download time

When "Save parameter set in non-volatile memory" is enabled in the download dialog (STARTER: Load to target system > Additional settings > Copy RAM to ROM), the CU executes p0977 = 1 immediately after the final block. The bulk write to the internal non-volatile memory produces a sustained USB stall. STARTER V4.3 does not release the USB pipe during this window, which is the trigger for the BSOD on hosts whose USB stack is intolerant of multi-second stalls.

3.4 Corrupted parameter set on the CU

If the CU was previously loaded with a project that contains a parameter outside the firmware-allowed range, the commissioning state machine enters a recovery loop on the next download. The 94% mark is the point where the loop collides with the upload protocol. A factory reset (p0970 = 1 with p0010 = 30) clears the state and produces a known-good baseline.

4. Pre-Download Verification Checklist

Before performing a download to the CU240E-2 DP, confirm each row of the following table:

5. Resolution: Primary Path (PM Connection plus STARTER Reinstall)

The field-verified resolution is a two-step action:

1. Connect the PM to the CU before any download attempt. The PM provides the 24 V backplane power that the CU needs during parameter commits. USB alone is not sufficient for programming.
2. Reinstall STARTER 4.3 (or upgrade to a later version). The fresh install replaces the SiemensUsbDriver stack and registers the correct S7ONLINE access point.

Procedure:

1. Power down the drive, disconnect mains from the PM.
2. Wait at least 5 minutes for the DC link capacitors to discharge; confirm the DC link LED is off before handling the CU.
3. Confirm the CU is firmly seated on the PM. The two retaining screws must be torqued to 1.5 Nm.
4. Reconnect mains, wait for the RDY LED to be steady green.
5. From Windows Control Panel, uninstall STARTER. Reboot.
6. Reinstall STARTER V4.3 SP3 (or, preferably, V4.5 SP1) from the original Siemens DVD or the official Siemens download. The installer auto-registers S7ONLINE (STEP7) -> Device (Starter, Scout).
7. Open STARTER, open the project, click Load to target system. With "Copy RAM to ROM" still unchecked, the download completes in < 30 s on a typical CU240E-2 DP.
8. After successful download, manually execute Target system > Copy RAM to ROM from the menu. This is the second-stage save that the original blocked transfer was trying to perform.

6. Resolution: Disable RAM-to-ROM During Download

If the PM is already connected but the BSOD persists, the next suspect is the in-dialog "Save RAM to ROM" flag. Disable it as follows:

1. Open the project, right-click the drive in the project navigator, choose Load to target system > Expert > Load.
2. In the "Load" dialog, click Additional settings.
3. Uncheck Save parameter set in non-volatile memory (Copy RAM to ROM).
4. Confirm with Finish.
5. When the load completes, manually copy RAM to ROM via the menu bar: Target system > Copy RAM to ROM.

This approach is the second most common field resolution. The third most common is to upgrade STARTER to V4.5 SP1 or to switch to Startdrive in TIA Portal V16 or later, where the USB-PNIC bridge is handled by the Siemens PCU USB driver and the load window is shorter. Reference: Siemens Support Entry 109763120 — Startdrive for SINAMICS G120.

7. PG/PC Interface Access Point Configuration

STARTER uses the S7ONLINE access point. The access point determines which physical device is used for the load. The CU240E-2 DP with USB cable requires the entry "Device (Starter, Scout)". The wrong entry routes the load to a virtual COM port that the CU does not have, which can also produce a hang at 94% but without a BSOD.

To set the access point:

1. Open Windows Control Panel.
2. Open Set PG/PC Interface (32-bit control panel applet — STARTER V4.x is 32-bit; on 64-bit Windows the applet must be run from %SystemRoot%\syswow64\control.exe).
3. Under Access Point of the Application, select S7ONLINE (STEP7) -> Device (Starter, Scout).
4. Under Interface Parameter Assignment Used, select the USB TCP/IP entry that points to the CU. If no entry exists, click Properties > New and add the CU USB Ethernet-over-USB interface (default IP 169.254.11.22, subnet 255.255.0.0).
5. Click OK, close the applet, restart STARTER.

Reference: Siemens Support Entry 48955385 — Setting the PG/PC Interface for STARTER.

8. Alternative Commissioning via BOP-2

If STARTER cannot be made to load at all, fall back to the BOP-2 Basic Operator Panel (6SL3255-0AA00-4CA1). The BOP-2 communicates with the CU via the diagnostic interface (RJ45) on the front of the CU and does not use the USB stack. Parameter uploads, downloads, and factory resets are possible from the BOP-2 menu tree.

To perform a factory reset from the BOP-2:

1. Plug the BOP-2 into the CU RJ45 diagnostic port.
2. Navigate to Menu > Parameter > Filter > All parameters.
3. Set p0010 = 30 (commissioning filter = factory reset).
4. Set p0970 = 1 (start factory reset).
5. Wait for the CU to complete the reset (about 30-90 s; the RDY LED flashes orange during the write).
6. Set p0010 = 0 to close the commissioning filter.

After the reset, re-attempt the STARTER download. The 94% hang should no longer occur because the parameter set is back to a known-good state. The BOP-2 also allows you to inspect active faults (Menu > Diagnostics > Active faults) without any USB connection, which is useful for confirming whether the CU is damaged.

9. Factory Reset Procedure via STARTER

If the BOP-2 is unavailable, the factory reset can be initiated from STARTER once a partial online connection is achieved (the connect works, the download does not):

1. Open STARTER, go online with the CU (right-click > Go online). This step does not require a download.
2. Open the expert list (right-click the drive > Expert list).
3. Set p0010 = 30 and acknowledge with the "Apply" button.
4. Set p0970 = 1 and acknowledge. The CU performs the reset.
5. Reconnect in STARTER. The connection will drop during the reset and re-establish once the RDY LED returns to steady green.

10. Hardware Damage Indicators

If the PM is connected, the "Copy RAM to ROM" is unchecked, the STARTER version is current, the PG/PC interface is correct, and the factory reset has been performed, and the 94% BSOD still occurs, the CU is likely damaged. The damage is typically on the USB PHY or the 24 V to 5 V regulator. Confirm with the following tests:

Relevant fault codes for a CU240E-2 DP that fails the 94% load test:

Reference: SINAMICS G120 List Manual — Fault and Alarm List.

11. Verification Tests After Resolution

After applying the resolution, run the following verification matrix:

12. Field Notes and Pitfalls

• Do not hot-plug the USB cable. The CU USB port is not designed for hot-plug during an active load. Always stop the load in STARTER (cancel button) before unplugging.
• Do not load a project whose firmware version (p0018) does not match the CU installed firmware version. Mismatched loads produce A01007 and can corrupt the parameter set, leaving the CU in a state that only a factory reset recovers.
• Do not run a third-party backup or antivirus scan during the load. The bulk USB writes look like mass storage activity to backup software, and the backup client may open the file handle at the same time the load is committing the parameter block.
• When upgrading STARTER, always install STARTER before installing the Startdrive add-in. Reverse order produces a registry collision on the S7ONLINE access point and the 94% symptom reappears even on a known-good drive.
• On Windows 11, the legacy STARTER V4.3 requires the 32-bit ODBC drivers to be installed. Without them, the project save produces a silent error that surfaces as a 94% hang on the next load.
• If you must use PROFIBUS instead of USB, the 94% symptom does not appear; the DP stack handles the long write without crashing. The PROFIBUS connection is therefore a useful diagnostic step: if the load works over DP but not USB, the issue is host-side.
• After a successful download over USB, always perform the manual Copy RAM to ROM step before powering off the PM. The download only writes to RAM; without the non-volatile save, the parameters are lost on power cycle.

13. FAQ