Resolving Siemens MasterDrive VC Fault F002: DC Link Diagnosis

1. Problem Statement: Intermittent F002 on a MasterDrive VC

The Siemens SIMOVERT MASTERDRIVES Vector Control (VC) drive, catalog number 6SE7016-1EA61-Z with option Z=G91, has been reported to trip on fault F002 intermittently within the first 20 operating hours. The fault is non-deterministic: the drive will refuse to start on several attempts, then begin operating normally, only to repeat the trip hours or days later. A replacement unit shipped under warranty subsequently triggered a Safe Off alarm that the option code should not have permitted, prompting a second warranty swap and a factory field engineer visit. This article isolates the F002 root cause, ties it to the DC link measurement path, and walks through the diagnostic and verification sequence used to clear the fault in production.

2. F002 Fault Definition

On the 6SE70 platform, F002 = DC link voltage measurement error. The control board (CUVC) samples the DC bus through an isolated voltage divider on the inverter power stage, digitises the result, and compares it against the firmware model. When the sampled value disagrees with the model by more than a fixed tolerance for a defined time window, the drive declares F002 and inhibits pulse enable.

The fault should not be confused with F001 (DC link overvoltage) or F004 (DC link undervoltage), which are threshold trips on a known-good measurement. F002 means the measurement itself is untrustworthy, so the drive refuses to enable rather than risk operating from a corrupt bus value.

3. Affected Drive: 6SE7016-1EA61-Z, Z=G91

The 6SE70 catalog is decoded as follows for the unit in question:

• 6SE7016 – Compact PLUS frame size, 400 V class, approximate 5.5–7.5 kW continuous output.
• 1EA61 – Vector Control (VC) firmware, CUVC control board, standard IGBT inverter.
• Z=G91 – Customer-specific option, typically a special firmware variant, connector pin-out, or label set. Confirm the option sheet shipped with the drive before assuming standard parameter defaults.

Reference the official SIMOVERT MASTERDRIVES Compendium (6SE70) and the 6SE70 Operating Instructions on Siemens Industry Online Support to confirm the exact frame size, rated current, and option interpretation. The ratings sticker on the drive (typically on the side of the heatsink) is the authoritative source for kW, A, and input voltage range.

4. Root Cause Analysis: The DC Link Measurement Chain

The DC link voltage is measured through the following chain, and a defect at any stage can produce F002:

1. DC bus capacitor bank – supplies the actual voltage to be measured.
2. Precharge / soft-charge circuit – limits inrush at line connect; if it is open, the bus may not reach the model-predicted value during the precharge window.
3. Isolated voltage divider on the IVI (Inverter) board – scales the bus to a level the CUVC ADC can read.
4. Optocoupler / isolation barrier – provides the galvanic isolation between power stage and control.
5. CUVC control board ADC channel – digitises the scaled value.
6. Firmware model and tolerance check – r006 is the final read-back; if the firmware self-check on this read-back fails, F002 is raised.

Reported root causes for F002, in order of frequency in the field:

5. The Safe Off (SSTO) Complication

The replacement drive in the source incident raised a Safe Off alarm, which on the 6SE70 family is implemented as the Safe Standstill (SSTO) safety function. SSTO requires the safety option hardware to be present – typically order codes K80 or similar – and gates the IGBT gate-drive signals through a redundant hardware path so that the motor cannot develop torque.

Safe Off typically ties to parameter r049 / P980 and the safety SS1 / STO timing parameters. On a non-safety drive that raises Safe Off, reflash or replace the CUVC firmware to the build matched to the option code. Confirm the firmware build with the MASTERDRIVES Compendium firmware matrix.

6. Pre-Diagnostic Safety Checks

Before opening the drive, complete these safety steps without exception. The 6SE70 DC bus retains lethal voltage for the discharge time printed on the front cover (typically 5 minutes after line removal for this frame size).

1. Lock out and tag out the upstream disconnect.
2. Wait the full discharge interval posted on the drive.
3. Measure the DC bus at the test points (TB1 on most 6SE70 Compact PLUS units) with a properly rated meter. Confirm < 5 VDC before contact.
4. Verify the motor is mechanically free to rotate or is decoupled.
5. Document r006, r008, r047, r049, P515, P516, P518 from the keypad before powering down. Use DriveMonitor or the OP1S operator panel.

7. Step-by-Step Diagnostic Procedure

Follow this sequence to isolate the F002 cause with a minimum of board swaps.

Step 1 – Capture the fault buffer

On the OP1S panel: navigate to Menu > Parameters > r047 and record the last eight faults with their time stamps. F002 appearing repeatedly without F001/F004 (overvoltage/undervoltage) confirms a measurement rather than a threshold event.

Step 2 – Monitor r006 live

With the drive enabled and unloaded, observe r006 (DC link voltage actual). For a 400 V class drive the expected value is approximately 540 VDC at no load with a 400 VAC three-phase supply. A reading that:

• Reads zero – open in the voltage divider, broken sense wire, or IVI board defect.
• Reads a constant offset – ADC calibration drift on the CUVC.
• Fluctuates wildly – intermittent solder joint, failing optocoupler, or noisy grounding.
• Is correct at no-load, errors at load – optocoupler linearity failure or motor-side transient injection.

Step 3 – Verify the model value

Compare r006 to the model value computed by the firmware. The drive predicts the expected DC link from the rectified line voltage (P017 / r017). If the predicted and measured values diverge, the measurement hardware is suspect, not the firmware model.

Step 4 – Measure the bus directly

With the drive de-energised and discharged, measure the resistance from each DC bus test point to the corresponding ADC input on the CUVC edge connector. Compare to the schematic in the operating instructions. An open reading identifies a broken trace or cold joint.

Step 5 – Inspect the IVI (Inverter) board

Remove the IVI board and visually inspect under magnification. Reflow any suspect solder joints, particularly the voltage divider and optocoupler pins. Reinstall and re-test. This step alone resolves a majority of intermittent F002 faults on drives with low operating hours.

Step 6 – Test the motor cable and insulation

Megger the motor windings and the cable to ground. A winding with degraded insulation can inject common-mode transients that the CUVC interprets as a measurement error. Disconnect the motor leads at the drive terminals and re-test; if F002 disappears, the issue is downstream.

Step 7 – Evaluate capacitor health

Measure DC link ripple with an isolated scope probe on the bus test points. A healthy 400 V class bus shows < 5 % peak-to-peak ripple at full load. Excessive ripple combined with F002 indicates capacitor ESR increase and warrants an IVI / capacitor bank replacement.

8. Parameter Reference

The following MasterDrive VC parameters are central to F002 diagnosis. Always confirm against the parameter list shipped with your firmware build; numbers below are representative for the standard CUVC firmware family.

9. Repair vs. Replacement Decision

With only 20 hours on the clock, the unit is well inside the infant-mortality window. The decision tree:

• Repair on-site – reflow IVI solder joints, replace optocoupler, replace capacitor bank. Cost-effective if the IVI is accessible and the shop is equipped for through-hole / SMD rework.
• Warranty swap – justified in the source case, but verify the replacement carries the same firmware build and option code. A swap that changes the CUVC firmware can introduce the Safe Off issue seen in the source thread.
• Factory refurbishment – preferred when the drive carries a safety option, when the fault is intermittent (suggesting intermittent component failure), or when a Siemens field engineer is already on site.

When requesting a warranty replacement, supply Siemens with the r047 fault buffer, the operating-hours counter (r049), and the Z-option sheet. This package allows the repair depot to correlate the failure with any known batch issue and to ship a replacement with a verified firmware build.

10. Verification & Commissioning

After the repair or replacement, complete this verification sequence before releasing the drive to production.

1. Power the drive with the motor disconnected. Run a no-load test of at least 30 minutes, monitoring r006 for stability.
2. Apply load in 25 % steps up to 100 % rated current. Hold each step for 10 minutes and log r006, r008, the heatsink temperature, and the fault buffer.
3. Cycle the drive on and off ten times, with a 2-minute run and 1-minute stop, to exercise the precharge circuit. No F002 should occur.
4. Confirm all three input line phases are present and within tolerance; loss of a phase can produce F002 on some firmware builds.
5. Verify the Safe Off / SSTO behaviour matches the option code. On a non-safety drive, the Safe Off bit must remain low at all times.
6. Capture the final commissioning parameter dump (DriveMonitor trace or OP1S upload) and file it with the drive's serial number.

11. Troubleshooting Matrix

12. Documentation & Escalation Path

If the F002 recurs after a warranty replacement, escalate through the following channels with the listed evidence:

1. Open a Siemens Industry Online Support ticket (SIOS) referencing the drive serial number and the previous RMA.
2. Attach the r047 fault buffer, the r006 log, and the option sheet.
3. Request a Siemens field engineer visit, citing intermittent measurement-class fault with infant-mortality operating profile.
4. If the engineer visit confirms a batch issue, request a coordinated firmware audit of all 6SE7016-1EA61-Z, Z=G91 units on site.

For the latest MASTERDRIVES documentation, firmware listings, and safety advisories, consult the SIMOVERT MASTERDRIVES Compendium and the 6SE70 Operating Instructions on Siemens Industry Online Support.