SIMOREG 6RA2287 F21 Fault: o7-o1-o3 Phase Trip on Start

The Siemens SIMOREG 6RA2287-4DV62-0 is a member of the SIMOREG DC-MASTER 6RA22 compact series of fully digital, four-quadrant DC drives used for armature and field control of DC motors in heavy industrial applications such as rolling mills, paper machines, hoists, and large extruders. A recurring fault scenario reported in the field is: the drive commands a start from status o7 into o1, but almost immediately falls back through o3 into o7, sometimes raising F21. The root cause is almost always traced to one of three subsystems: the A2 (trigger / control) board, the A3 (line-side monitoring) board, or the K2 / K5 relay interlock chain. This reference walks through drive identification, status codes, the A2 / A3 architecture, the K2 / K5 logic, F21 specifics, and an end-to-end field diagnostic procedure.

1. Drive Identification and Model Decoding

The order number 6RA2287-4DV62-0 decodes as follows for the SIMOREG 6RA22 family:

Note: confirm the exact MLFB (Maschinenlesbare Fabrikatebezeichnung) with the nameplate on the unit before ordering spares. The same suffix can ship with different firmware releases (for example -0 versus -0AA0). Always cross-check the firmware version shown on the OP1S / PMU panel under parameter r060 (or its firmware-rev equivalent) before downloading a parameter set, swapping boards, or applying a firmware update.

2. Operating Status Phases (o7, o1, o3)

The SIMOREG 6RA22 expresses its high-level operating state through a numeric status phase shown on the OP1S / PMU operator panel and exposed in the drive state word (typically r001.001 on standard firmware). The states that appear in this fault scenario are:

The reported sequence o7 → o1 → o3 → o7 is the diagnostic signature of a start that is accepted by the control electronics but aborted because the line-side monitor on A3 never confirms the presence of armature mains. If the abort raises a fault, an Fxx code (most commonly F21 in this family) is latched; if no fault is raised, the drive simply reverts to o7.

3. F21 Fault Code Definition

On the SIMOREG 6RA22 family, F21 is the diagnostic code raised when the external pulse-cancellation (also documented as "pulse disable" or "external fault - pulse inhibit") input on the A2 board is active. On the A2 terminal strip, this input sits between terminals 7 and 8:

• Terminal 7: Pulse cancellation input (active level depends on the parameterization of P-Group 7xx).
• Terminal 8: Reference / return for the pulse cancellation input.

When terminals 7 and 8 are not bridged (or are connected through an external interlock that has opened), the trigger unit refuses to fire the SITOR pulses and raises F21. F21 typically forces the drive to status o7, drops the main contactor command through K2, and latches a fault entry in the diagnostic buffer.

4. A2 and A3 Board Architecture

The control electronics of a 6RA22 stack onto a small set of plug-in boards. The two boards that matter for the F21 / o7-o1-o3-o7 scenario are A2 and A3.

4.1 A2 - Trigger Unit / Control Electronics

The A2 board hosts the field-oriented control, the gate-firing logic, and the low-voltage I/O terminals (terminals 1 through approximately 30 on the front-edge connector). Key signals for this fault scenario:

On the A2 board, two relays play the central role in the start / fault logic:

• K2 - Main contactor command relay. When energized, K2 closes the upstream main contactor that feeds the armature AC bus.
• K5 - Fault signaling relay. K5 drops (de-energizes) on any internal fault condition (fuse failure, parallel SITOR fault, missing mains) and its contacts are wired to the A3 board and to an external fault bus.

4.2 A3 - Line-Side Monitor

The A3 board is the line interface board. It carries:

• Opto-isolated line-voltage sensors (one per phase) that confirm the presence and phase sequence of the armature AC supply.
• Fuse-failure detection for the parallel SITOR bridge fuses.
• The interface to the K5 fault relay and to the main contactor status feedback.
• In some hardware revisions, a small phase-sequence monitor that locks out the start if R-S-T is mis-wired or if the phase rotation is reversed.

On a start command, the A2 board commands K2 to close. Once the contactor is mechanically picked up, AC mains appears at the drive's power input. The A3 optos must confirm this presence within a configured time window (typically a few hundred milliseconds). If A3 cannot confirm - because of a blown fuse, a miswired phase, or a contactor that did not actually close - A3 commands K5 to drop, and the drive reverts to o7 and may raise F21 if the pulse-cancellation input is wired into the same interlock chain.

5. K2 / K5 Logic Chain

The interaction between the K2 command relay, the A3 line monitor, and the K5 fault relay is the heart of the o7-o1-o3-o7 loop. The intended sequence is:

1. Operator issues Start (terminal 17 releases OFF1, terminal 18 closes Enable).
2. A2 control logic asserts the K2 coil. K2 closes the main contactor; mains is applied to the armature input.
3. A3 optos detect the three-phase mains within the monitoring time window. A3 also checks phase sequence and the integrity of the SITOR fuses.
4. If step 3 succeeds, A3 holds K5 energized and the drive progresses from o1 (run-up) into closed-loop current / torque control.
5. If step 3 fails, A3 de-energizes K5. K2 is released, the contactor drops out, the drive raises an Fxx code (or just a status), and the drive returns to o7.

6. Root Cause Analysis

From the reported behavior, the candidate root causes rank as follows:

The original symptom (o7-o1-o3-o7 plus intermittent F21) typically points to a combination of #1 and #3: the A3 line monitor is marginal, and the external interlock on terminal 7-8 is occasionally bouncing. Both should be addressed.

7. Step-by-Step Diagnostic Procedure

Use this procedure on a locked-out, de-energized drive where safe electrical work practices (LOTO) are in place. The drive should be in o7 before each test.

7.1 Confirm Safe State

1. Open the upstream disconnect. Apply lockout / tagout.
2. Verify zero energy on the armature AC bus and on the field supply with a known-good voltage tester (CAT III / IV rated for the installation).
3. Wait the capacitor discharge time stamped on the cabinet (typically 5-10 minutes for 6RA22 sizes).
4. Verify zero DC bus voltage at the test points provided on the front of the unit.

7.2 Visual Inspection

1. Open the drive door. Inspect the SITOR fuses - any discolored fuse body, cracked fuse tube, or black soot means the fuse has failed. Replace in sets, even if only one fuse is visibly blown.
2. Inspect the A2 and A3 boards for dust, condensation, capacitor bulging, or burn marks.
3. Confirm the terminal block at the front of A2 is fully seated; the cage clamps on these terminal strips loosen over years of thermal cycling and are a leading cause of intermittent o7-o1-o3-o7 faults.
4. Check the A3 board for the small three-phase connector. A partially seated connector is enough to lose one phase to the opto sensor.

7.3 Verify the F21 Path (A2 Terminal 7-8)

1. With the drive in o7 and locked out, measure continuity across A2 terminals 7 and 8. The path should be either a low-resistance bridge or a closed contact of the customer-supplied interlock.
2. If the interlock is a normally-closed contact (door interlock, fan monitor, thermal sensor), check its continuity separately.
3. If you temporarily bridge 7-8 with a short jumper (only for diagnosis, remove before returning to service), the F21 condition should clear. If F21 clears with the bridge in place, the customer wiring or the interlock device is the problem, not the A2 board.
4. Inspect the cage clamp on terminal 7. The wire is often stranded and one or two strands break off during installation; the contact becomes marginal and the circuit opens under vibration.

7.4 Verify the A3 Line Monitor

1. Re-energize the upstream feed but leave the drive in o7 (do not issue a start command yet).
2. On the OP1S / PMU panel, navigate to the line-voltage diagnostic. On 6RA22 hardware, the relevant parameters are typically r025 (line voltage, line frequency) and r026 (line status). All three phase-to-phase voltages should read within a few percent of the nameplate mains.
3. If any phase reads 0 V or wildly low, the problem is upstream - check the contactor, the bus, and the cable glands.
4. Watch the LEDs on the A3 board (where fitted). Most A3 revisions have three LEDs that mirror the opto sensors. A missing LED is a strong indicator of a phase problem.
5. Measure the DC bus voltage with a scope. The bus should rise smoothly to the peak of the AC line within 50-100 ms of the contactor closing. Asymmetric half-cycles or a slow rise point to a single-phase condition.

7.5 Verify the K2 Contactor Command

1. Issue a start command from the panel (or force a software start via the OP1S menu).
2. Listen and feel the main contactor. It must close within roughly 200 ms. If it hums but does not close, the coil is likely under-volted or the armature is stuck.
3. Use a scope or a DMM with min / max capture to watch the line voltage at the drive input the moment the contactor closes. Voltage sag or chatter indicates weak mains or a weak contactor.
4. If the contactor closes but A3 still does not confirm mains, the contactor aux contact (the one feeding the A3 confirmation logic) may be the problem. Aux contacts are mechanical and wear out long before the main contacts.

7.6 Isolate the K5 Relay

1. Locate K5 on the A2 board. It is typically a small industrial relay in a clear socket.
2. With the drive powered but in o7, measure the K5 coil voltage. It should be at the rated coil voltage (typically 24 VDC).
3. Pull K5 from its socket and substitute a known-good relay of the exact same part number. If the o7-o1-o3-o7 loop clears, K5 was the problem.
4. Inspect the K5 socket for oxidation or bent pins; both are common on drives older than 10 years.

7.7 A2 / A3 Board Swap

1. If all of the above have been ruled out, the most likely remaining cause is the A3 board itself (opto sensor failure, phase-sequence monitor IC failure) or the A2 board (gate-firing logic failure).
2. Swap A3 with a known-good board of the same hardware release. Boards are keyed; do not force a wrong-revision board into the slot.
3. If the loop clears with the swapped A3, send the original A3 to a repair shop for opto and phase-monitor IC replacement.
4. If the loop persists, swap A2. Note: swapping A2 may require re-loading parameters from a backed-up parameter set or from the commissioning disk.

8. Signal and Terminal Mapping Reference

9. Component Replacement Notes

• SITOR fuses: Replace in sets of three (one per phase). Use only Siemens SITOR fuses of the exact part number printed next to the fuse holder. Mixing brands or underrated fuses is a common cause of repeated fuse failure.
• K2 and K5 relays: Use the relay Siemens specifies on the A2 board BOM. Aftermarket relays with the same pinout but different coil characteristics are a recurring source of intermittent trips.
• A2 / A3 boards: These are ESD-sensitive. Use a wrist strap. Do not touch the gold edge connectors. Boards must be re-parameterized if the firmware revision differs from the original.
• Main contactor: If the contactor aux contacts are pitted, replace the contactor. Do not file the aux contacts - the plating is critical for the low-level signal that the A3 optos read.
• Cooling fan: Drives older than 7 years often have degraded fans. A slow fan can trip the A3 thermal input on some hardware revisions and masquerade as a line-monitor fault.

10. Parallel SITOR Bridge Topology

The 6RA2287 uses parallel SITOR (Siemens Thyristor) modules to achieve the high DC armature current that the MLFB implies. Each phase of the armature bridge is typically built from two or more SITOR modules in parallel, with a fuse in series with each parallel leg. This has two consequences for fault finding:

1. Fuse-failure detection is per-leg, not per-phase. A single blown fuse on one parallel leg will not always show as a missing phase on the AC side, but will show as DC-bus asymmetry on the load side. A scope on the DC bus is the only reliable way to detect it.
2. Current sharing between parallel legs must be verified. Loose bus bars or oxidized contact surfaces cause one parallel leg to carry more than its share of current, leading to chronic fuse failures and eventually to K5 dropping on the A3 board's fuse-failure input.

11. Verification Tests

1. With the drive back in o7, remove the lockout and re-energize.
2. Confirm the panel reads o7 and no fault is active.
3. Issue a start from the panel. Confirm the sequence progresses o7 → o1 → run with no transient o3.
4. Run the motor to 25%, 50%, and 100% of setpoint and hold each for at least 30 seconds. Watch for F21 or any other fault.
5. Capture a parameter snapshot (DriveMonitor / STARTER export) for the maintenance record.
6. Document the final parameter set on a label inside the cabinet door.
7. Repeat the start sequence at least three times in succession to rule out a marginal condition that only fails on thermal expansion.

12. Field-Proven Caveats and Safety

13. Parameter and Diagnostic Snapshot

Before replacing any board, capture the full parameter set. The minimum useful snapshot for this scenario is:

14. Cross-References to Siemens Documentation

The following official Siemens documents are the authoritative references for the 6RA22 family. Use them to confirm any value you read here against the manual shipped with your specific unit:

• Siemens Industry Online Support - SIMOREG DC-MASTER 6RA22 series entry portal
• SIMOREG DC-Master 6RA22 Operating Instructions (compact series)
• SIMOREG DC-Master 6RA22 Function Description / Parameter List
• SIMOREG DC-Master 6RA22 List of Faults and Alarms

For ordering spares, the SIMOREG Spares On Web (SOW) tool inside Siemens Industry Online Support lets you key in the MLFB and pull up the exact A2, A3, K2, K5, and SITOR fuse part numbers for your hardware release.

FAQ