26001

Check Deceleration Parameters

Navigate to HMI > Parameters > Machine Data and verify MD32300 (max axis acceleration) and MD32310 (max axis deceleration) are not set too aggressively for your motor/load combination.

Reduce deceleration values by 20-30% initially to test if regeneration is the issue

Verify Brake Resistor Circuit

Check MD1418 (brake resistor enable) is set to 1 and MD1419 (brake resistor value) matches your installed resistor. Measure actual resistor value with multimeter.

Ensure drive is powered down and locked out before measuring brake resistor

Monitor DC Bus Voltage

Use HMI > Diagnostics > Drive > Actual Values to monitor r0026 (DC bus voltage) during normal operation and note peak values during deceleration cycles.

Values consistently above 750V on 400V systems indicate insufficient regenerative capacity

Adjust Voltage Monitoring Windows

If hardware is confirmed good, temporarily increase MD1410 (overvoltage threshold) by 5-10V to provide additional headroom while addressing root cause.

This is a temporary measure only - do not exceed manufacturer specifications

Measure Incoming Line Voltage

Use power quality analyzer to measure L1, L2, L3 voltages at the drive input terminals. Check for voltage imbalance >2% and total harmonic distortion >5%.

Monitor for at least one complete machine cycle to capture voltage dips during high-load operations

Check Line Reactor and Fuses

Verify line reactor connections are tight and measure DC resistance across each phase. Check input fuses for proper rating per drive manual specifications.

Loose connections can cause voltage drops and generate dangerous heat

Review Voltage Monitoring Parameters

Access HMI > Parameters > Drive and verify MD1411 (undervoltage threshold) is set appropriately for your supply voltage tolerance, typically 15% below nominal.

For unstable supplies, consider enabling MD1412 (undervoltage delay time) to prevent nuisance trips

Check Capacitor Visual Condition

Power down system and inspect DC bus capacitors for bulging tops, electrolyte leakage, or discoloration. Note capacitor manufacture date codes.

DC bus capacitors retain lethal voltage - use proper lockout procedures and wait minimum 10 minutes after shutdown

Measure Capacitor ESR

Using ESR meter, measure equivalent series resistance of DC bus capacitors. Values >20% above nameplate specifications indicate degradation.

Capacitors typically need replacement after 7-10 years in industrial environments

Monitor Ripple Voltage

Use oscilloscope to measure AC ripple on DC bus (r0026). Excessive ripple >5% of DC value indicates capacitor issues.

Perform this measurement during normal machine operation to see actual load effects

Check Drive Status LEDs

Examine all status LEDs on drive modules. Red LEDs indicate hardware faults. Cross-reference LED patterns with drive manual fault codes.

Take photos of LED status for Siemens technical support if escalation is needed

Review Drive Diagnostic Buffer

Access HMI > Diagnostics > Drive > Fault Buffer and check for additional fault codes that may indicate hardware issues like rectifier or chopper faults.

Look for patterns of multiple simultaneous faults which often indicate hardware rather than application issues

Perform Drive Self-Test

Execute drive internal diagnostics via HMI > Service > Drive Test functions to verify internal monitoring circuits and power stage functionality.

Some drive tests require motor disconnection - follow proper safety procedures

Verify Motor Configuration Data

Check HMI > Parameters > Drive and confirm MD1082 (motor rated voltage), MD1083 (motor rated current), and MD1084 (motor rated power) match motor nameplate exactly.

Even small discrepancies in motor data can cause significant control issues

Validate Drive Scaling

Verify MD1086 (motor rated speed) and MD1087 (motor rated frequency) are correctly entered. Run automatic motor identification if available.

Use MD1900 (motor identification) to automatically determine motor parameters if unsure

Check Control Mode Settings

Confirm MD1300 (control mode) is appropriate for your application and MD1400 series voltage controller parameters are properly configured.

Incorrect control modes can cause unstable operation and damage equipment