Resolving the "E" Error on SIMOVERT MASTERDRIVES 6SE70 PMU Display After CUVC/CBP2/T300 Board Transfer

The SIMOVERT MASTERDRIVES 6SE70 family (also catalogued under the legacy SIMOVERT VC compact units 6SE702x) is still widely deployed in process, marine, and metals industries. The Parameterization Unit (PMU) on the front of the CUVC control board is a 7-segment + alphanumeric display that surfaces drive state, fault numbers, warnings, parameter values, and operating modes. A single character "E" on the PMU is one of the most frequently misinterpreted indications because it is not a fault code in the Fxxx sense, nor is it a warning in the Axxx sense. It is the drive's boot-mode flag, and it commonly appears after a board swap, after a firmware corruption event, or whenever the 24 V control supply path is disturbed.

This reference consolidates the diagnostic logic, the field-tested recovery steps, and the compatibility matrix needed when moving a CUVC + CBP2 (PROFIBUS) + T300 (technology) set between a 6SE7023-4TC61-Z and a 6SE7024-7TD61-Z, or when commissioning either inverter from a DC-link-only forming source.

1. Problem Description and Affected Hardware

The reported scenario involves two compact units, both with IP20 enclosures and 510–650 V DC link ratings:

Symptom: After removing the CUVC, CBP2, and T300 boards (plus the slot D/E adapter and LBA) from the 6SE7023-4TC61 and installing them into the 6SE7024-7TD61, the receiving drive shows only the character "E" on the PMU. The CBP2 board LED does not illuminate, indicating that the PROFIBUS slave never came out of initialization. The DC link is fed from a forming/auxiliary circuit (no line-side rectifier active), so 400 V AC line is not present at L1/L2/L3 during commissioning.

2. PMU Display Code Reference for MASTERDRIVES 6SE70

Before assuming a fault, decode the PMU character using the standard MASTERDRIVES legend. The display is the small 4-digit / 2-character unit on the front of the CUVC; it shares the same hardware as the 7-seg indicator used on the SLB and SCB.

3. Root Cause Analysis: Why the Drive Stays in "E"

Three mechanisms can leave a 6SE70 in boot mode after a board swap. The field engineer must eliminate them in this order:

1. Boot-mode switch is active. The CUVC carries a 2-pin boot-mode header (commonly referenced as X-bridge or "boot" on the silkscreen) that forces the on-board microcontroller into its loader. If the previous service engineer set this jumper to enable a firmware update and left it in place, the replacement drive will boot into "E" regardless of how healthy the firmware image is. This is the single most common cause after a board move.
2. Firmware CRC failure at startup. If the firmware stored in flash on the donor CUVC is for a different CUVC variant (e.g., motion-control firmware loaded onto a vector-control unit, or firmware compiled for a different power stage rating), the boot ROM detects the mismatch and refuses to launch the application. The display falls back to "E".
3. Corrupted 24 V logic supply. If the internal 24 V aux rail is sagging, noisy, or absent on a sub-circuit (e.g., the CBP2 or T300 3.3 V / 5 V local regulators cannot derive a stable rail), the CUVC may reset continuously and present "E" between resets. CBP2 LED off and T300 not visible on the LBA bus are typical symptoms.

Eliminating the supply issue first is mandatory because attempting a firmware upload on a drive with marginal 24 V will brick the loader itself.

4. Hardware Architecture: CUVC, CBP2, T300, LBA, and Slot Adapter

The 6SE70 control platform is a stack of PCBs connected through the backplane of the electronics box (E-box). Understanding the slot map is essential before swapping boards between two different frame sizes.

The 6SE7023-4TC61-Z includes the K01 + K11 combination, meaning the donor was a fully populated multi-axis-capable drive. The 6SE7024-7TD61-Z with G91 (slot A only) was a single-axis PROFIBUS slave. When transferring a CBP2 from slot C to a drive whose firmware is configured for slot A, the firmware may not initialize the CBP at the new physical slot. The error visible is "E" because the CUVC falls back to loader mode, not because the CBP itself is broken.

5. Compatibility Matrix: Moving CUVC + CBP2 + T300 Between 6SE7023-4TC61 and 6SE7024-7TD61

The two compact units share the same CUVC hardware (both are vector-control, both use the same electronics box width 100 mm / 150 mm), but their power-stage firmware parameters differ. The CUVC stores rating-plate data in non-volatile parameters r070, P070 series and power section identifiers that the firmware uses to enforce current limits. A CUVC pre-configured for a 34 A power section will refuse to start a 47 A power section; in some firmware builds it returns to "E" because the safety check fails before modulation is enabled.

6. DC-Link-Only Operation and Forming Circuit Requirements

The 6SE70 compact units are designed to accept either a 3-phase AC line on L1/L2/L3 (with the built-in diode bridge forming the DC link) or a pre-formed DC link fed into P600/N600. In a DC-link-only cabinet (common in multi-drive common-bus systems), the line is disconnected and the DC link is sourced from a separate 6-pulse or active-front-end rectifier. When commissioning a drive in this topology:

• Apply the forming circuit per the MASTERDRIVES Compendium, Edition 02/2005, Section 4.3 — limit inrush with a 2 kΩ / 100 W resistor and a 10-second ramp.
• Verify that the DC link reaches 510 V minimum before 24 V aux is enabled on the CUVC. If the aux supply comes up before the DC link is formed, the CUVC can brown-out during its initialization and remain in boot mode.
• The 24 V aux for the CUVC electronics is typically sourced from the internal PSU on the power stack; when running DC-link-only with no AC line, this internal PSU is offline, so an external 24 V source (Siemens 6EP1 or equivalent, fused at 2 A) must be wired to the auxiliary terminal block per the wiring diagram in the operating instructions, 6SE7080-series parameter list.

If the external 24 V is absent or marginal, the CUVC will not boot at all, and the PMU stays blank. If the 24 V is present but noisy, the CUVC may repeatedly enter and exit boot mode, occasionally showing "E" between reset cycles. Always confirm 24 V at the CUVC terminals X9/1 (+) and X9/2 (–) with a scope — not just a DMM — to rule out ripple above 100 mV pk-pk.

7. 24 V DC Supply and PMU Power Diagnostics

The PMU is fed from the same 5 V regulator that supplies the CUVC microcontroller. A failure here is sometimes misread as a "drive in boot mode" condition.

7.1. Isolated Power Test

1. Disconnect every external signal wire from the CUVC, CBP2, and T300 — control terminals, encoder, PROFIBUS cable, fiber SCI, and the PMU ribbon.
2. Apply 400 V AC three-phase to L1/L2/L3 of the drive through a step-down isolation transformer with a current-limited output (5 A breaker upstream). This energizes the internal 24 V aux rail from the line-side transformer on the power stack.
3. Observe the PMU. The display must show – – – – (standby) or o.n (operating) within 5 seconds.
4. If the PMU still shows E, the 24 V path is internal and the CUVC board is the suspect.
5. If the PMU shows – – – – normally, the 24 V is healthy — the problem is on the board stack or in the firmware, not the supply.

7.2. PMU Loopback

The PMU is a passive 7-segment + key panel on a 10-pin ribbon (X109 on the CUVC). Reseat the ribbon and inspect for oxidization. A cracked ribbon or a cold solder joint on the CUVC connector will mimic a boot-mode display by garbling the segments into a single "E".

7.3. CBP2 Power-Up Check

The CBP2 draws its 5 V and 3.3 V from the backplane LBA. If the LBA K11 is not seated, or if the SCI fiber is broken and the CBP2 is configured for SCI-routing, the CBP2 will not enumerate. Always:

• Verify the CBP2 is fully seated in its slot (the front bezel must be flush with the E-box frame).
• Confirm the LBA K11 is present and its two retaining screws are torqued (0.6 Nm typical).
• Check that the SCI fiber from the previous node is either looped with a fiber loopback or terminated at the donor's CBP2 — an open SCI fiber is a known cause of a CBP2 that never comes out of initialization.

8. Step-by-Step Recovery Procedure

1. Lock out and verify zero energy. Open the DC-link feeder, wait 5 minutes, measure P600 to N600, then to chassis, with a Cat IV 1000 V meter. All three readings must be 0 V.
2. Remove the CUVC, CBP2, and T300 from the 6SE7024-7TD61. Lay them on an ESD-safe mat. Photograph the slot order before any further work.
3. Inspect the CUVC for the boot-mode jumper. Look for a 2-pin header near the firmware-flash chip (U150 area, silkscreen "BOOT" or "BR"). Confirm the jumper is in the OFF / NORMAL position. The factory default is OFF.
4. Verify the firmware chip and the CUVC variant marking. The CUVC has a hardware code (e.g., 6SE7090-0XX84-...) printed on the EEPROM label. This must match the firmware build stored in flash; mismatches are the second most common cause of persistent "E".
5. Re-seat all boards into the target 6SE7024-7TD61: CUVC in slot 1, CBP2 in slot A (matching the G91 option, not slot C), T300 in slot D (if the slot adapter K01 is installed), and LBA K11. Tighten the retaining screws.
6. Apply the DC-link forming circuit and bring the DC link to 540 V (nominal 400 V line equivalent).
7. Enable the 24 V aux on the CUVC. The PMU should illuminate within 3 seconds.
8. Observe the PMU.
   • If – – – – appears: the boot-mode jumper was the issue, recovery complete.
   • If E persists: proceed to firmware upload via DriveMonitor (see Section 9).
   • If the PMU is blank: return to Section 7.1 and check the 24 V supply.

9. Firmware Update and Parameter Download via DriveMonitor

When the PMU remains in "E" after the supply checks, the firmware must be reloaded. The legacy toolchain for the 6SE70 is DriveMonitor 5.5 (or the successor Drive ES 5.x for the SIMOVERT family). The newer TIA Portal Starter/Commissioning tool can also be used via the USS/Modbus route, but DriveMonitor remains the most reliable for the 6SE70 platform.

9.1. Required Cabling

• Serial RS232 cable (6SE7090-0XX84-... adapter or USB-to-RS232 with FTDI chip) from the PC to the PMU service port X108 on the CUVC.
• Baud rate: 19 200 (default), 8 data bits, even parity, 1 stop bit, no handshake. This is set in DriveMonitor under Settings → Online.

9.2. Loading Firmware from an Image File

1. Open DriveMonitor 5.5, select Online → Drive → Firmware Download.
2. Point to the firmware file matching the CUVC variant. For a vector-control compact, the file is typically named VC_nnnn.fw where nnnn is the build number. Verify the build matches the 6SE70 power section — a motion-control firmware on a vector-control board is a known boot-loop cause.
3. Confirm the boot-mode jumper is in the ON position only for the duration of the upload. Return it to OFF once DriveMonitor reports "Firmware loaded successfully".
4. Cycle the 24 V aux to the CUVC. The PMU should advance from E to – – – – and then to the parameter number P000 within 5 seconds.

9.3. Downloading a Parameter Set (Cargo Pump .dnl)

A typical field scenario: the drive has been re-flashed and is now empty. The application parameters (the "cargo pump" parameter set) must be downloaded from a .dnl file. With the drive in "E" mode, parameter download is not possible — DriveMonitor will report "Drive not in OPERATIONAL state". You must first complete the firmware upload so the drive leaves boot mode, then perform the parameter download.

1. After firmware upload and PMU showing P000, navigate to Online → Parameter → Download in DriveMonitor.
2. Select the .dnl file matching the application (in this case, the cargo pump set).
3. DriveMonitor prompts for a factory reset — accept, and confirm the prompt for parameter 970 (parameter set restore).
4. After the download, cycle 24 V once more and verify that the drive is back in – – – – with the expected parameter values in r000 (drive type) and r070 (power section code).

9.4. Pre-Upload Checklist

• Confirm the boot-mode jumper is ON for the upload, OFF afterwards.
• Confirm 24 V aux is stable within ±5 % during the upload (a brown-out mid-upload bricks the loader).
• Back up any readable parameters via DriveMonitor Online → Parameter → Upload before starting, even from a board in "E" mode — DriveMonitor can read the firmware identifier and the boot-loader revision even in boot mode.

10. Verification and Commissioning Checks

After the recovery procedure, run the following verification before releasing the drive to production:

11. Common Pitfalls and Field-Engineered Notes

• Re-flashing the same firmware does not clear "E". If the boot-mode jumper is the root cause, the firmware upload will appear to succeed but the drive will return to "E" the moment the jumper is moved back to OFF. Always verify the jumper position before and after any flash operation.
• A CUVC from a different frame size carries a different power-section calibration. Even if the firmware is identical, the current-loop tuning parameters and the IGBT desaturation thresholds are board-level. Mixing a 34 A CUVC into a 47 A drive without a full parameter reset is a frequent cause of F0011 (overcurrent) within the first 200 ms of modulation — not the symptom being investigated here, but it shows up as a follow-up fault once "E" is resolved.
• SCI fiber must be terminated or looped. A dangling SCI fiber on a removed CBP2 will keep the LBA in a fault state and the CBP2 will not enumerate. Use a Simatic fiber loopback (6GK1900-1BE00-0AA0 or similar) on the unused SCI port.
• Forming-circuit timeout. The 6SE70 expects to see the DC link at 510 V minimum within 30 seconds of 24 V aux. If the forming circuit is too slow, the CUVC may interpret the rising DC link as an undervoltage condition and remain in "E"-like initialization. Verify the forming resistor value and the time constant per the Compendium.
• PMU ribbon oxidation. In marine and offshore installations, the X109 ribbon accumulates sulfur. Clean with isopropyl alcohol and reseat. If the ribbon is brittle, replace it — the symptom can be a phantom "E" even on a fully booted drive.
• DriveMonitor 5.5 on Windows 10 / 11. Run as Administrator and disable driver signature enforcement for the USB-RS232 driver if the legacy FTDI driver is not recognized. DriveMonitor 5.5 is dated 2006 and Microsoft has dropped the unsigned-driver path several times since.

12. Summary Diagnostic Matrix

The "E" indication is rarely a sign of a dead CUVC. In nearly every documented case it is either the boot-mode jumper left in the ON position after a previous firmware update, a firmware-version mismatch introduced by a board swap across power-section boundaries, or a 24 V aux supply that is just out of spec. A 10-minute check of the jumper, the 24 V rail, and the firmware build resolves the majority of field calls without a board return to the repair center.