MM440 Runs in Reverse at -15Hz: Analog Input Not Responding Fix

MM440 Runs in Reverse at -15Hz and Ignores the Analog Setpoint: Field Troubleshooting Guide

The Siemens MicroMaster 440 (MM440) is a robust general-purpose inverter, but field engineers frequently encounter a startup fault pattern in which the drive immediately accelerates to -15 Hz in the reverse direction and the analog setpoint has no effect. The visible symptoms are unmistakable:

• ON command is applied, motor rotates backwards.
• Output frequency clamps at -15 Hz regardless of the analog reference.
• Increasing the analog signal (4-20 mA or 0-10 V) does not raise the speed.
• Changing the value at the keypad or via P1000 has no effect.

The root cause is almost always a corrupted parameter set in which a fixed frequency (P1001-P1015) has been assigned to a negative value, combined with a command source that selects that fixed frequency instead of the analog input. The remedy is a parameter reset to factory defaults followed by a clean re-commissioning. This guide walks through the diagnostic path, the reset procedure, and the verification steps that confirm correct operation.

1. Why the MM440 Defaults to -15 Hz in Reverse

The MM440 supports two independent setpoint sources selected by index on P1000:

When the drive ignores P1000=2 (analog setpoint) and rotates backwards at a fixed -15 Hz, the most common cause is that one of the additional setpoint indices still points to a fixed frequency with a negative value. The MM440 sums the active setpoint sources, so a -15 Hz fixed frequency combined with 0 Hz analog reference yields a net setpoint of -15 Hz regardless of what the operator does at the analog terminal.

Common setpoint sources on MM440 (valid for all P1000 indices):

Many field technicians only inspect P1000.0 and miss the fact that P1000.1 or P1000.2 is still set to a fixed frequency left over from a previous commissioning. Always enumerate all three indices when diagnosing a runaway setpoint.

2. Related Parameters That Cause a -15 Hz Reverse Run

The -15 Hz value is suspiciously specific. It often originates from a fixed frequency parameter that was set during a previous test or commissioning and never cleared. Inspect the following parameters in order:

Note the function of P0701 through P0708: these assign digital input functions. A common wiring fault is to assign ON reverse (value 2 or 12) to DIN1 inadvertently, or to leave a digital input configured for fixed frequency selection (value 15, 16, 17, 18). When a digital input is mapped to fixed frequency selection, the active FF is added to the main setpoint. With a negative fixed frequency, the motor reverses immediately.

If any digital input is mapped to value 2, 12, or 15-18 and that input is high, the drive will run in reverse or sum a fixed frequency. A factory reset clears all of these.

3. Diagnostic Procedure Before Reset

Before resetting, capture the current parameter set so that a known-good configuration can be restored. Use the BOP (Basic Operator Panel), AOP (Advanced Operator Panel), or STARTER commissioning software. If a PC connection is not available, transcribe the parameters manually.

3.1 Enable Expert / Service Access

Many of the parameters in question are at access level 2 or 3:

1. Set P0003 = 3 (Expert level). On older firmware, you may need P0003 = 2 first to access P1000, then P0003 = 3 for full diagnostics.
2. Set P0010 = 0 to allow online parameter changes (commissioning parameter).

3.2 Verify the Analog Input With r0752

The parameter r0752 is a read-only display of the actual analog input scaled value in percent. Use it to confirm the wiring and signal type:

1. Navigate to r0752[0] for Analog Input 1 (terminals 3, 4) and r0752[1] for Analog Input 2 (terminals 10, 11).
2. Apply 0%, 50%, and 100% of the configured range (for example 4 mA, 12 mA, 20 mA for 4-20 mA).
3. Verify the displayed value moves from 0% to 50% to 100% respectively.

Reference scaling parameters for the analog input:

If r0752[0] shows 0% even with the analog signal applied, the wiring is wrong, the signal type (P0756) is mismatched to the hardware jumper, or the analog ground is floating. The MM440 has a slide switch on the control board between terminals 3 and 4: position it for V (voltage) or I (current) input to match the PLC or instrument output. The same applies to terminals 10 and 11 for AI2.

3.3 Read the Active Setpoint With r0020 / r0021

The active setpoint after all source summation is shown in r0020, and the actual output frequency in r0021. When the drive is at -15 Hz with the analog input at minimum, expect:

• r0020 = -15.00 Hz (or the negative value of the offending fixed frequency)
• r0021 = -15.00 Hz

If r0020 is positive but r0021 is negative, the sign comes from a reverse command (P0701=2 or P0701=12) rather than the setpoint.

3.4 Check for Stuck or Wired-Reverse Digital Inputs

Inspect the status word r0722 (bit 0 = DIN0, bit 1 = DIN1, etc.) to see which digital inputs are HIGH. If DIN1 is HIGH and P0701=2 (ON reverse), the drive will run in reverse. This commonly happens when a control relay is wired to the wrong terminal or when a wire from a previous installation is left on a terminal block.

4. Factory Reset Procedure (Parameter P0970)

The confirmed remedy from the field is to perform a full parameter reset using P0970. There are two levels: user-level reset and factory reset.

4.1 Reset via the BOP / AOP Keypad

1. Stop the drive. Remove the ON command from the digital inputs.
2. Navigate to P0003 and set it to 1 (for the simplified reset) or to 2 if you want to access P0970 with full access.
3. Navigate to P0010 and set it to 30. Press P to confirm. The drive is now in reset mode.
4. Navigate to P0970 and set it to 1 (or 21 for a true factory reset).
5. Press P to confirm. The display flashes, then shows busy, then ready.
6. Wait until the display returns to the standard operating screen (no busy message). This can take 5 to 30 seconds.

4.2 Reset via STARTER or StartDrive Commissioning Software

1. Connect to the drive via USS, PROFIBUS, or RS232 (use the PC-inverter connection kit 6SE6400-1PC00-0AA0 or the USB-to-RS485 adapter 6SE6400-1PL00-0AA0 for older MM440).
2. Go online and upload the current parameter set for backup (Upload from device).
3. Open the Commissioning wizard and choose Factory Reset, or navigate to P0970 in the parameter list.
4. Set P0010 = 30, P0970 = 21, and click RAM to EEPROM (or transfer to the drive).
5. Power-cycle the drive to ensure the reset is persistent. On some firmware versions the reset is only effective after a power cycle.

5. Re-Commissioning for 0-10 V or 4-20 mA Analog Control

After a factory reset, all parameters return to defaults. Reapply the configuration for the analog-controlled forward-only application.

5.1 Required Parameters for 0-10 V Forward Control

5.2 Disable Reverse Rotation

If the application does not require reverse rotation, lock the direction:

1. Set P1110 = 1 to inhibit negative setpoints (the drive clamps to 0 Hz if a negative setpoint is requested).
2. Set P1031 = 0 to disable the reverse jog (the MOP/reverse jog function).
3. Set P0702 = 0 (or whatever DIN is wired to reverse) to disable the reverse command input.

6. Verification Steps

After re-commissioning, perform the following verification sequence before reconnecting the load.

1. Apply 0% analog (0 V or 4 mA) and read r0021. It must read 0.00 Hz.
2. Apply the ON command on DIN1. The drive should accelerate to the setpoint dictated by the analog signal.
3. Slowly raise the analog signal to 50% and observe r0021 = 25.00 Hz (for 0-50 Hz scaling).
4. Raise to 100% and observe r0021 = 50.00 Hz (or the configured max).
5. Remove the ON command. The drive should ramp down to 0 Hz at the rate of P1121.
6. Reverse polarity on the analog input (if supported) and confirm the drive remains at 0 Hz with P1110 = 1.

If the drive still runs reverse, check the digital input status word r0722 for an unexpected HIGH on a reverse-mapped input, then verify that no control cable is crossed between forward and reverse on the terminal block (terminals 5, 6, 7, 8, 9 on the MM440 control card).

7. Analog Signal Type Checklist

Match the hardware and the parameter to the PLC or instrument output:

For a 4-20 mA signal with P0756[0] = 4, the MM440 applies a deadband below 4 mA so that the scaled value remains at 0%. The deadband width is set in P0761[0] in mA. A typical value is 2 mA, which makes the deadband extend from 0 to 2 mA and 4-20 mA scale linearly to 0-100%.

8. Common Faults That Mimic the Symptom

9. Saving and Documenting the Commissioned Set

After verification, save the parameter set to avoid re-commissioning the next time the drive is replaced or downloaded:

1. In STARTER, choose Upload from device and save the project file (.dps or .sdp).
2. On the BOP/AOP, use the optional SD card slot to write the parameter file to an SD card (AOP only).
3. Document the parameter values in a spreadsheet, including the firmware version displayed in r0018 (for example 04.00.05.00 for a 4 kW MM440, FW 4.05).

For long-term reliability, set P0014 = 21 on some firmware versions to enable "save parameters in EEPROM on every change" (default behavior on newer MM440 firmware; older firmware may require manual EEPROM save).

10. Quick Reference Reset Card

11. Frequently Asked Questions