238-1003

Measure incoming AC voltage

Using a true RMS multimeter, measure voltage at the main input terminals to the UM power supply module (L1, L2, L3). Verify all three phases are present and balanced within 2% of each other. Nominal should be 400-480VAC depending on machine specification.

Only qualified electricians should perform measurements on high voltage AC supply. Lockout/tagout procedures required.

Check supply circuit breakers and contactors

Inspect the main supply contactor (typically K1 in machine schematics) and verify all three poles are closing properly. Check circuit breaker for thermal trip or degraded contacts causing voltage drop under load.

Measure voltage both upstream and downstream of contactors under load - a voltage drop >5V indicates contact degradation.

Monitor voltage during alarm occurrence

If alarm is intermittent, use a power quality analyzer or the PLC diagnostic input monitoring to capture voltage levels during machine operation when the alarm triggers. This identifies transient voltage sags from facility power issues.

Check with facility maintenance if heavy loads (welders, presses) share the same supply transformer - coordinated start-up sequences may be required.

Check UM module age and operating hours

Review the UM power supply module manufacturing date (label on module) and machine operating hours. Modules over 7-8 years old or with >40,000 operating hours are candidates for preventive capacitor-related failures.

Document the serial number and order replacement modules proactively for older systems - lead times can be 6-12 weeks.

Monitor DC bus voltage ripple

Access MOD 9 → Service Mode → Diagnosis → Drive diagnosis. Select the relevant UM module and monitor DC bus voltage during axis movement. Look for excessive ripple (>30V peak-peak) or voltage sag during acceleration that recovers slowly - both indicate capacitor degradation.

This diagnostic requires machine operation under supervision - ensure proper safety zones and E-stop accessibility.

Perform capacitor test if equipped

Some UM modules have built-in capacitor diagnostics accessible via Service Mode. Navigate to MOD → Diagnosis → Power Supply → Capacitor Test. Follow on-screen prompts to execute the automated test sequence which measures capacitance and ESR.

If capacitor test is not available, compare DC bus voltage rise time during power-up between suspect module and known-good module - degraded capacitors show slower charging curves.

Replace UM power supply module

If capacitor degradation is confirmed, replace the entire UM power supply module. After installation, verify DC bus voltage is stable at 560-650VDC (400V systems) and perform axis tuning verification via MOD → Test Run → Axis Test to confirm proper operation.

Discharge DC bus capacitors before module removal - wait minimum 5 minutes after power disconnect and verify <40VDC with meter.

Review axis motion program at alarm time

In Programming and Editing mode, review the NC program that was executing when alarm occurred. Look for rapid deceleration commands (short deceleration distances, emergency feed holds) especially on heavy axes like rotary tables or Z-axes with counterbalance.

Use the Execution Trace function (MOD → Trace → Execution) to capture exact block and feed rate at time of fault - this shows deceleration profile.

Verify brake resistor installation and rating

Check electrical cabinet for brake resistor installation (typically mounted on cabinet wall or external heat sink). Verify resistor value matches UM module specification label (typical values: 47Ω, 68Ω for 400V systems). Measure actual resistance with ohmmeter - should be within ±10% of rating.

Brake resistors can remain hot for 30+ minutes after operation - verify cool to touch before handling.