SV0433

Measure AC Input Voltage

Use a true RMS multimeter to measure voltage across L1, L2, and L3 terminals at the servo amplifier while the machine is powered on. Ensure readings are within ±10% of rated voltage (200-230VAC for 200V class, 380-480VAC for 400V class).

Measure during peak load conditions (e.g., during rapid axis movement) to catch intermittent sags.

HIGH VOLTAGE: Ensure proper insulation on probes and wear PPE to avoid electric shock.

Check Voltage Balance

Verify that the voltage difference between phases (L1-L2, L2-L3, L1-L3) is less than 5%. Significant imbalance can cause DC link issues even if individual voltages are within spec.

If imbalance is detected, check upstream power distribution or consult with facility electrician.

Do not proceed with machine operation if imbalance exceeds 5% as it risks further damage.

Monitor Voltage Over Time

Use a data-logging multimeter or power quality analyzer to record AC input voltage for at least 30 minutes during normal operation to detect transient brownouts or sags.

Compare logged data with machine alarm timestamps to correlate voltage drops with SV0433 alarms.

Ensure logging equipment is rated for industrial voltage levels to prevent damage.

Check Equipment Age

Review maintenance records or serial number data to determine the age of the servo amplifier. Units older than 8 years are prime candidates for capacitor failure.

Look for bulging or leaking capacitors during visual inspection as a quick indicator.

None for this step.

Measure DC Link Ripple Voltage

With machine powered on, use an oscilloscope to measure ripple voltage on the DC link bus (refer to amplifier manual for test points). Ripple should be less than 10% of nominal DC voltage (e.g., <27V for 270VDC threshold).

Set oscilloscope to AC coupling mode to isolate ripple from DC component for accurate reading.

HIGH VOLTAGE: DC link can carry up to 750VDC. Ensure proper safety protocols and wait 5 minutes after power-off before accessing test points.

Perform Substitution Test

If ripple is excessive or age suggests failure, temporarily swap the PSM module with a known good unit (if available) to see if the alarm clears. If it does, replace the original module.

Label all connections before swapping to avoid miswiring during reinstallation.

Ensure machine is locked out and DC link voltage is below 42VDC before swapping modules.

Visual Fuse Inspection

Power off and lock out the machine. Inspect fuses F1-F3 on the PSM module or external supply disconnect for visible damage, discoloration, or a broken filament.

Check fuse holders for signs of overheating or arcing, which can indicate recurring issues.

Do not touch fuses until main power is verified off and locked out.

Test Fuse Continuity

Remove each fuse and use a multimeter in continuity mode to test for an open circuit. Replace any fuse that fails the test with an identical rating as per the amplifier manual.

Keep spare fuses of the correct rating on hand to avoid downtime during testing.

Using incorrect fuse ratings can cause catastrophic failure—verify specs before replacement.

Check Upstream Breakers

Inspect and test upstream circuit breakers in the electrical cabinet supplying the amplifier for tripped status or failure. Reset or replace as needed.

If breakers trip repeatedly, investigate for short circuits or overloads before resetting.

Ensure zero voltage verification before accessing breaker panel.

Inspect Resistor Assembly

Power off and lock out the machine. Visually inspect the regenerative discharge resistor for burnt elements, cracks, or disconnected wires.

Take photos of the assembly before disassembly for reference during reinstallation.

Do not test while powered—high-energy discharge can cause severe burns.

Measure Resistor Value

Use a multimeter to measure the resistance across the resistor terminals. Compare to specification in the amplifier manual (typically 40-80 ohms depending on model).

If value is significantly off, replace the entire resistor assembly rather than individual elements.

Ensure machine is de-energized and wait 5 minutes for DC link discharge before testing.

Test Thermal Switch Continuity

Check the thermal switch on the resistor assembly for continuity using a multimeter. An open switch indicates overheating or failure—replace if defective.

If switch is open, check for airflow obstructions or cooling fan issues around the resistor.

Verify zero voltage before accessing switch terminals.

Visual Terminal Inspection

Power off and lock out the machine. Inspect AC input terminals (L1, L2, L3) on the servo amplifier for corrosion, burn marks, or loose wires.

Look for green oxidation on copper terminals as a sign of moisture ingress.

Do not inspect while powered—arc flash risk is high with loose connections.

Torque Terminal Connections

Using a torque wrench, tighten all terminal screws to the manufacturer’s specification (typically 1.2-1.5 N·m). Ensure no strands of wire are outside the terminal.

Use a wire brush to clean corroded terminals before re-tightening if oxidation is present.

Over-torquing can strip threads—use a calibrated tool.

Check Ground Connection

Verify the ground terminal connection is secure and free of corrosion, as poor grounding can exacerbate voltage issues. Tighten to spec and clean if necessary.

Apply dielectric grease to ground terminal after cleaning to prevent future corrosion.

Ensure lockout/tagout is in place before accessing ground terminal.