Troubleshooting Siemens SIMOVERT F002 Pre-Charging Fault

Overview of F002 on SIMOVERT Masterdrives

The SIMOVERT VC 6SE70 family (commercially known as Masterdrives) reports F002 when the control electronics detect either a pre-charging failure of the DC link or a fault in the DC-link voltage measurement path. Unlike a simple overcurrent or overvoltage event, F002 is a supervisory fault: the firmware never sees the DC bus reach the expected voltage within the configured window, or the sensed value disagrees with the plant voltage by an amount the firmware considers implausible.

On a 400 V class unit such as the 6SE7041-2WL60-Z referenced in field reports, the nominal rectified DC-link voltage is approximately 540 V DC at full line voltage. If the firmware expects the bus to reach this level within the pre-charge time (typically a few seconds) and either the bus stays low, rises too slowly, or the analog sensing path reports a value far from the actual bus, F002 trips at the first start command and the inverter will not modulate.

Affected Drive Models and Hardware Architecture

Field reports of F002 concentrate on the following Masterdrives variants:

The 6SE70 architecture relevant to F002 is split across three boards that all participate in DC-link supervision:

• PSU (Power Supply Unit): Generates the 24 V and 15 V rails for control electronics, monitors the DC-link voltage through a dedicated divider, and supplies the fan circuit via onboard fuses. A failure here directly raises F002 because the firmware never receives a valid DC-link measurement.
• CUVC (Vector Control electronics): The main control board. Reads the DC-link signal routed from the PSU, executes pre-charge supervision, and raises F002 via the fault word. Some variants place a divider network directly on CUVC.
• Power section: Contains the rectifier, the pre-charge resistors and contactor (or pre-charge IGBT in some variants), the DC-link capacitors, the IGBT inverter bridge, and the DC-link fuses. Any component here can also manifest as F002.

Documentation for the platform is found in the Siemens Masterdrives operating instructions, available through the Siemens Industry Online Support portal under the SIMOVERT MASTERDRIVES product family. The Masterdrives VC parameter list and the function block library are the primary references for parameter codes referenced in this article.

F002 Root Cause Matrix

The following matrix consolidates the field-confirmed root causes plus the standard interpretation of the fault. Use it to choose a starting branch in the diagnostic tree.

Pre-Diagnostic Safety and Prerequisites

Working inside a SIMOVERT Masterdrives requires explicit safety steps because the DC link remains charged for several minutes after line removal.

1. Lock out and tag out the upstream three-phase feed. Verify zero potential at the line terminals with a properly rated tester.
2. Wait a minimum of five minutes after power removal before opening the cabinet. Confirm the DC-link has discharged by measuring across the DC bus bars with a DMM rated to 1000 V DC. A reading above 50 V means the link is still live.
3. Verify the DC-link short-circuit between DC+ and DC- on the bus bars. The pre-charge resistors and the bus capacitance together store dangerous energy; do not rely on the front-panel indicator alone.
4. Use a CAT III 600 V or CAT IV 600 V meter. Standard household DMMs are not rated for the energy stored in a Masterdrives DC link.
5. Have replacement fuses of the correct rating ready: 690 V 25 A 10x38 gG for European spares, or 63 A American Type for North American spares. Do not substitute a higher rating; the fuse protects the pre-charge path.

Step-by-Step Diagnostic Procedure

Follow this sequence before swapping any board. Each step rules out one or more root causes cheaply.

1. Confirm the symptom: Power the drive with no command. Measure DC bus voltage across DC+ and DC- on the bus bars. A reading between 510 V and 580 V on a 400 V class unit is normal at no-load. If the bus is missing or below 400 V, focus on input fuses and rectifier.
2. Read r006: Use the operator panel (OP1S) or DriveMonitor to read parameter r006 (DC-link voltage). Compare it to the DMM reading at the bus bars. They should agree within 5 %. A large mismatch (for example bus = 540 V, r006 = 300 V) points to the CUVC or PSU voltage divider rather than the power section.
3. Give the start command: Listen for the pre-charge contactor closing. A loud click with no further sound is normal. A faint hissing or crackle followed by F002 indicates a CT or insulation failure, not a parameter problem.
4. Check the PSU status LED and 24 V rail: With the drive powered, the PSU should have a green status LED and the 24 V test point should read between 23.5 V and 25.5 V. A missing LED or absent 24 V means the PSU is the primary suspect.
5. Inspect input and DC-link fuses: With the drive locked out and the DC link discharged, pull each input fuse holder and measure continuity. Pull the DC-link fuse blocks and measure the same way. A failed fuse is itself a symptom, not the cause; find the load that drew the overcurrent.
6. Inspect CUVC voltage-sense divider: With the CUVC removed, measure the high-impedance divider resistors on the board. Reference values depend on the specific CUVC variant; an open or high-resistance resistor explains the F002.
7. Megger the motor and cable: Disconnect the motor leads from the drive output terminals U, V, W and run a 500 V or 1000 V insulation test from each phase to ground. A reading below 1 MΩ indicates insulation breakdown and a probable source of F002 if the cable run is long.
8. Diode-test the IGBTs: With the drive locked out and discharged, remove the control ribbon from the IGBT driver board. Measure each IGBT in diode mode from collector to emitter and gate to emitter. A shorted device pulls the DC bus down through the pre-charge resistors and trips F002 at the next start.

Diagnostic Flowchart

PSU Board Diagnostics

The PSU is the most common single-board cause of F002 reported in field cases. The board performs three jobs relevant to the fault: it derives the 24 V rail for the control electronics, it routes the DC-link voltage to the CUVC, and it supplies the fan circuit through one or two fuses.

Test points and checks:

• Measure 24 V DC between the PSU test pads marked +24 V and 0 V. A reading below 22 V or above 26 V means the PSU is out of specification and must be replaced.
• Inspect the fan-circuit fuse (often a small 5x20 mm glass fuse on the PSU PCB). A blown fan fuse can coexist with F002 because the firmware may interpret a stalled fan as a pre-charge supervision fault on some firmware versions.
• Look for bulging electrolytic capacitors near the DC-link sense input. The divider capacitors in particular are known to drift in high-temperature service.
• Examine the ribbon cable between PSU and CUVC. A loose or oxidized connector produces intermittent F002 that is hard to catch on a static test.

CUVC Board and DC-Link Voltage Sensing

The CUVC reads the DC-link voltage routed from the PSU and passes it to the firmware as r006. On some CUVC variants, the divider resistors sit directly on the CUVC PCB; on others, they sit on the PSU and only the conditioning op-amp is on the CUVC. Confirm by inspecting the PCB silk screen: resistors marked Rxxx near the DC-link input connector belong to the divider.

Symptoms of a divider failure:

• r006 reading 300 V or other implausible value while the actual bus is normal (540 V on 400 V class).
• F002 trips the instant the start command is given, with no audible contactor closure.
• The fault clears when the CUVC is swapped for a known-good board and the original is reinstalled.

Repair options are limited. The divider is typically a matched pair of high-value resistors; if one is open, replace both with the same value and the same tolerance. Do not substitute standard 1 % resistors for the original matched pair; the firmware assumes a specific divider ratio and a non-matched pair will produce persistent r006 errors.

Current Transformer (CT) Verification

The current transformers on Masterdrives sit on the AC line side and on the DC-link in some variants. They provide feedback for current control and for short-circuit detection. A CT with a shorted secondary or a saturated core can present a fault condition that the firmware flags as F002 because the measured current does not match the expected profile at start.

Field-proven diagnostic sequence for a suspect CT:

1. With the drive powered down and locked out, identify the suspect CT by visual inspection for discoloration, cracked resin, or a burnt smell.
2. Disconnect the CT secondary leads at the CUVC terminal block.
3. Measure the secondary DC resistance. Compare to a sister drive or to the manufacturer datasheet. A reading of 0 Ω indicates a shorted secondary; an open reading indicates a broken lead.
4. If the secondary is intact, perform a ratio test by injecting a low AC current through the primary and measuring the secondary. The ratio should match the nameplate within 5 %.
5. If no sister drive is available, the original field test is sufficient: swap the suspect CT with a known-good spare, re-energize, and observe. If F002 clears, the CT is the root cause.

DC-Link Fuses and Pre-charge Resistor Test

The pre-charge path on a 6SE70 consists of one or more power resistors in series with a dedicated contactor (or, on some variants, an IGBT pre-charge switch). The path is protected by an input fuse on the AC side and a DC-link fuse between the rectifier output and the inverter input. Both fuses are field-replaceable but must be specified correctly.

Specification values for the units discussed in this article:

Test procedure with the drive locked out and discharged:

1. Remove the fuse holders. Visually inspect the fuse elements for a clear break or a darkened glass body.
2. Measure continuity with a DMM on continuity mode. A good fuse reads below 0.5 Ω. A blown fuse reads open.
3. If a DC-link fuse is open, do not re-energize the drive until the cause is found. Open the inverter section and diode-test every IGBT. A shorted IGBT will re-blow the fuse within milliseconds of pre-charge.
4. Measure each pre-charge resistor. Values depend on the frame: a typical 6SE7041 pre-charge resistor measures in the 10 Ω to 50 Ω range. An open resistor disables the pre-charge path entirely and F002 will trip on the first start.

IGBT Module and Motor Cable Insulation Check

Field case data points to a recurring sequence: an overcurrent event (motor short, cable damage, IGBT failure) blows the DC-link fuse. The operator replaces the fuse and re-energizes. F002 trips because the underlying short is still present, and the new fuse blows again. The visible damage is then misattributed to a fuse problem when the real cause is downstream.

Procedure to break this cycle:

1. Lock out the drive. Disconnect the motor leads from terminals U, V, W. Insulate the cable ends.
2. Megger each phase-to-ground on the motor cable at 500 V or 1000 V. The reading must exceed 1 MΩ; readings in the kΩ range indicate insulation breakdown and the cable must be replaced or the run re-pulled.
3. Megger the motor windings the same way. A motor with water ingress or winding failure will show low insulation and is the root cause of F002 trips.
4. Diode-test every IGBT module on the inverter section. With the control ribbon disconnected, a healthy IGBT shows a diode drop of about 0.3 V to 0.7 V between collector and emitter in one direction only. A reading in both directions, or a short, means the module must be replaced.
5. After replacement, fit a new DC-link fuse and run a no-load start. If F002 no longer appears, the motor or cable was the cause.

Parameter and Configuration Verification

Parameter errors do not produce F002 as often as hardware faults, but they must be ruled out, particularly after a firmware upload or a parameter set restore from an incorrect backup.

Key parameters to check on the CUVC:

Always compare the current parameter set against the last known-good commissioning backup before assuming a hardware fault. The default set shipped with the drive is not always appropriate for the specific line impedance and transformer impedance at the plant.

Hissing Sound Diagnostic Clue

One of the most useful field-proven indicators of a current-sensing or insulation failure on the 6SE70 is a faint hissing or crackling sound audible at the moment the start command is given, immediately before F002 trips. The sound originates from one of two sources:

• Partial discharge in a degraded CT secondary winding: the inter-turn insulation has broken down under the inrush transient and the CT core is saturating audibly.
• Tracking in a motor or cable insulation defect: the high dV/dt of the pre-charge transient ionizes a weak point and produces an audible corona-like hiss.

If the operator reports a hissing sound coupled with F002, prioritize the CT swap test and the cable megger test before tearing into the PSU or CUVC. The sound is a strong negative indicator for parameter faults and a strong positive indicator for a hardware defect in the current or insulation path.

Field Repair Case Studies

The following are field-confirmed root-cause and resolution patterns extracted from maintenance reports on the 6SE7041-2WL60-Z and similar units.

Case 1: Defective current transformer

Drive raised F002 on every start command. DC bus voltage measured normal at the bus bars with a DMM. The technician swapped one CT for a known-good unit from a sister drive; F002 cleared. Re-installing the suspect CT brought the fault back. The repair was a CT replacement. A faint hissing sound at the start command was the diagnostic clue that pointed to a current-sensing fault rather than a pre-charge voltage fault.

Case 2: Blown rapid fuse

After extended troubleshooting, the technician opened the drive and found a blown rapid fuse in the pre-charge path. Replacing it with a 690 V 25 A 10x38 gG (European spec) or 63 A American Type restored operation. The original fuse had failed from age rather than a downstream short; this was confirmed by an IGBT diode test that read healthy on every module.

Case 3: Burnt DC-link fuse from secondary damage

The DC-link fuse was found blown, and the technician re-fused the drive twice. On the third event, an IGBT module was found shorted and the motor cable had visible damage at a flexing point near the gland. The correct sequence was to replace the IGBT module, re-pull the motor cable, and only then fit a new DC-link fuse. Skipping the IGBT and cable test caused repeated fuse failures.

Case 4: CUVC voltage-sensing resistors

r006 reported 300 V while the DMM measured 540 V at the bus bars. The mismatch pointed to the divider on the CUVC. Inspection found one high-value resistor in the divider drifted out of tolerance. Replacing the matched pair restored r006 to the correct value and F002 stopped tripping.

Case 5: PSU board end-of-life

The PSU 24 V rail measured 21.5 V under load, below the 22 V threshold the CUVC uses for valid DC-link sensing. The fan-circuit fuse on the PSU was also blown. Both faults contributed to F002. Replacing the PSU cleared both.

Verification and Commissioning After Repair

After any F002 repair, run a structured re-commissioning sequence:

1. Confirm the DC-link discharges below 5 V within five minutes of power removal.
2. Power up. Verify r006 matches the DMM reading at the bus bars within 5 %.
3. Issue a no-load start command. Confirm the pre-charge contactor closes, the bus reaches nominal voltage within the pre-charge window, and the drive transitions to Run without F002.
4. Issue three consecutive start/stop cycles. F002 that trips only on the first start after a long downtime is often a capacitor forming issue; F002 that trips consistently on every start is a hard fault.
5. Run the motor under light load. Monitor r018 against the nameplate FLA. A reading above 50 % FLA with no mechanical load points to a CT or current-sensing problem that has not been resolved.
6. Capture a fresh parameter backup via DriveMonitor or the OP1S and store it in the maintenance record. The next F002 event will be easier to diagnose with a known-good baseline.

Related Fault Codes and Cross-References

F002 rarely appears in isolation. The following fault codes commonly co-occur and provide diagnostic cross-references:

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