Original Siemens Precharging Board 6SE7031-7HF84-1HH2 6SE70317HF841HH2 6SE7O31-7HF84-1HH2 6SE7 031-7HF84-1HH2

Siemens 6SE7031-7HF84-1HH2 | SIMOVERT MASTERDRIVES PCU1 Pre-Charging Module Board — 380–575V, Design E & F

Part Number: 6SE7031-7HF84-1HH2

Manufacturer: Siemens AG (Germany)

Product Type: Pre-Charging Module Board (PCU1 — Pre-Charge Unit)

Product Range: SIMOVERT MASTERDRIVES (6SE70 Series) 

Overview

The 6SE7031-7HF84-1HH2 is the PCU1 pre-charging module board for Siemens SIMOVERT MASTERDRIVES chassis converters and inverters in design configurations E and F, operating on 380–575V three-phase AC supplies.

The PCU1 — Pre-Charge Unit 1 — is the electronic module responsible for controlling the controlled energisation of the DC bus capacitors in a SIMOVERT MASTERDRIVES chassis drive.

It is a board-level spare part for maintaining the pre-charging functionality in the installed base of SIMOVERT MASTERDRIVES equipment across industries.

The SIMOVERT MASTERDRIVES is Siemens' fully digital modular AC drive platform for high-performance industrial applications — a comprehensive product family covering converters, inverters, rectifier units, and regenerative feedback units for three-phase AC motor control across the 2.2kW to 2300kW power range.

MASTERDRIVES chassis units — the physical designs E and F that the 6SE7031-7HF84-1HH2 serves — are cabinet-mount drive assemblies at the medium-to-high end of the power range, deployed in rolling mills, paper machines, extruder lines, test stands, marine propulsion systems, and large material handling installations.

The suffix HH2 identifies this as the second revision of the HH-type PCU1 board for this drive family.

The preceding HH1 revision and HH0 revision were the earlier versions of the same board.

Revision HH2 incorporates component updates and reliability improvements while maintaining full functional and physical compatibility with the drive assemblies designed for the HH0 and HH1 revisions.

Key Specifications

Pre-Charging — Why It Is Critical

The DC bus in a SIMOVERT MASTERDRIVES chassis unit contains a bank of large electrolytic capacitors. These capacitors store significant energy — necessary for the drive's operation but also a safety consideration.

When the drive is powered on from a de-energised state, connecting the full AC supply voltage directly to uncharged capacitors would cause an inrush current surge large enough to damage the rectifier diodes, blow the DC bus fuses, and potentially damage the capacitors themselves.

The pre-charge circuit solves this problem by limiting the inrush current during DC bus charging.

The PCU1 board controls a series of pre-charge resistors and a bypass relay or contactor.

During the pre-charge phase, AC supply power flows through the resistors into the capacitors, limiting the charging current to safe levels. When the capacitors have charged to near the supply voltage peak — a process that takes a few hundred milliseconds — the PCU1 board signals the bypass relay to close, short-circuiting the resistors and connecting the full supply to the now-charged capacitors. The drive is then ready for normal operation.

If the PCU1 fails, the drive cannot complete its pre-charge sequence. The DC bus never reaches its operating voltage, and the drive remains in a non-ready state.

The symptom is typically a startup fault — the drive's PMU display shows a fault code indicating pre-charge failure or DC bus undervoltage, and the drive cannot be commanded to run.

SIMOVERT MASTERDRIVES Architecture — PCU1 in Context

The SIMOVERT MASTERDRIVES chassis drive assembly includes the rectifier/inverter power section, the DC bus capacitor bank, the control electronics (the CUD1 processor board and any option boards), and the auxiliary circuits that support startup and protection.

The PCU1 is one of these auxiliary circuits — specifically the board that controls the controlled startup of the DC bus.

In a converter unit (one that includes both the rectifier and inverter sections), the PCU1 monitors the incoming AC supply and manages the pre-charge sequence before the main contactor closes.

In a system with a separate inverter unit drawing from a common DC bus, the pre-charge circuit protects the inverter's own capacitors when the DC bus connection is made.

The 6SE7031-7HF84-1HH2 PCU1 board physically mounts within the drive chassis, interfaced to the pre-charge resistors and the bypass contactor or relay through internal drive wiring.

It also interfaces with the main control board (CUD1) through a control connector, allowing the control unit to monitor pre-charge status and issue the drive-ready signal once pre-charge is complete.

Fault Diagnosis

When the SIMOVERT MASTERDRIVES does not complete its startup sequence and shows a DC bus-related fault, the PCU1 board is a primary diagnostic focus.

The fault pattern — drive attempts startup, pre-charge sequence does not complete, drive goes to fault — is the typical PCU1 failure signature.

Before replacing the PCU1, verify the AC supply voltage at the drive input terminals.

A supply voltage outside the 380–575V range will prevent successful pre-charge regardless of the PCU1's condition. Also check the pre-charge resistors — if a pre-charge resistor has failed open-circuit, the DC bus cannot charge through it, producing a symptom identical to PCU1 failure.

The pre-charge resistors are often the more common failure component and should be tested first.

If the supply is within specification and the resistors are confirmed intact, the 6SE7031-7HF84-1HH2 has likely failed and requires replacement.

FAQ

Q1: The SIMOVERT MASTERDRIVES shows a fault immediately on power-on, before the DC bus has time to charge. The supply voltage is within specification. Is the PCU1 board the fault?

An immediate fault on power-on before the DC bus charges can indicate a PCU1 board that has failed to initiate the pre-charge sequence — possibly due to a failed control circuit or a damaged pre-charge control output. First verify the pre-charge resistors are intact.

Then check the control interface connectors between the PCU1 and the main CUD1 board. If both are confirmed good, the 6SE7031-7HF84-1HH2 board itself has failed and requires replacement.

Q2: The drive completes pre-charge successfully some of the time, but fails intermittently. Is this consistent with a failing 6SE7031-7HF84-1HH2?

Intermittent pre-charge failure is consistent with a PCU1 board that has an aging component — often a relay contact or an electrolytic capacitor — that is at the threshold of failure. The board functions when conditions are favourable (for example, when the board is cool) but fails when margins are reduced (when warm, or when supply voltage is at the lower end of the specified range).

This progressive intermittent failure will become permanent as the component degrades further.

Plan board replacement before the failure becomes complete and causes unplanned downtime.

Q3: The PCU1 board revision available is HH2, but the original installed was HH1. Are these interchangeable?

Yes. Revision HH2 is the direct successor to HH1 and HH0. Siemens maintains backward compatibility across PCU1 board revisions for the same drive design designations (E and F).

The HH2 revision incorporates reliability and component updates but is functionally and physically identical in its interface to the drive.

No additional commissioning is required after installing HH2 as a replacement for HH1.

Q4: The SIMOVERT MASTERDRIVES chassis has been in service for over 15 years. Beyond the PCU1, what other components should be inspected during a pre-charge-related service?

On a 15-year-old drive, the following should be checked alongside the PCU1 board: the pre-charge resistors for open-circuit or increased resistance, the bypass relay or contactor for worn contacts (check the contact resistance and the coil operating voltage), the DC bus capacitors for increased ESR and capacitance loss (which reduces the pre-charge time but can also cause heating), and the main rectifier fuses for any signs of thermal stress.

A preventive replacement of capacitors at this age is worth considering, as their service life in drive applications is typically 10–15 years.

Q5: Is the 6SE7031-7HF84-1HH2 still available, given that SIMOVERT MASTERDRIVES has been superseded by SINAMICS?

The SIMOVERT MASTERDRIVES 6SE70 series has been discontinued by Siemens, but spare parts including the PCU1 board remain available through the aftermarket supply chain — from specialist industrial drive service providers who maintain stocks of refurbished, tested spare boards.

For sites with multiple MASTERDRIVES chassis units, keeping a spare PCU1 board in stock is prudent given the risk of an unplanned shutdown if this board fails. 

Alternatively, sites with significant MASTERDRIVES investment may consider a planned upgrade to the SINAMICS platform as part of a capital investment programme.