231-8064

Check AC Input Voltage

Use a true RMS multimeter to measure voltage at the main power input terminals. Verify voltage is within ±10% of rated voltage (typically 400V/480V 3-phase).

Monitor voltage over several machine cycles to catch intermittent drops that may not show on a single reading.

Inspect Power Supply Connections

Check all AC input connections at the main disconnect, transformer, and control cabinet for loose connections, corrosion, or overheating signs.

Always use proper lockout/tagout procedures before inspecting electrical connections.

Monitor Facility Power Quality

Use a power quality analyzer to record voltage variations, harmonics, and transients over a 24-hour period to identify facility power issues.

Check if the alarm correlates with heavy machinery starting up elsewhere in the facility.

Verify TNC Power Supply Status

Access MOD function and check power supply voltages in the diagnostic screens to confirm internal DC voltages remain stable during AC variations.

Check DC Output Voltages

Measure all DC output voltages from the main power supply unit (+5V, +15V, -15V, +24V) under load conditions using the TNC diagnostic functions.

Compare readings against the power supply specification label - typically ±5% tolerance for digital supplies.

Inspect Power Supply for Physical Damage

Examine the power supply unit for bulging capacitors, burnt components, excessive dust buildup, or fan failure that could cause thermal shutdown.

Power supply capacitors can retain dangerous voltages even when power is off.

Test Power Supply Under Load

Run a complete machine cycle while monitoring power supply outputs with an oscilloscope to detect voltage ripple or momentary dropouts.

Pay special attention to the +5V rail as it's most critical for TNC operation and most sensitive to supply issues.

Check Power Supply Cooling

Verify cooling fans are operational and air filters are clean. Measure internal temperature if accessible - should be below 60°C during operation.

Test Main Circuit Breaker

Check the main circuit breaker for proper operation, correct amperage rating, and signs of arcing or overheating. Verify trip curves match machine requirements.

Aging circuit breakers can develop high contact resistance, causing voltage drops under load.

Inspect Main Contactor Operation

Examine the main contactor for worn contacts, proper coil voltage, and clean switching operation. Check contact resistance with a low-resistance ohmmeter.

Worn contactor contacts can cause arcing and voltage instability.

Verify Fuse Integrity

Test all fuses in the AC power path with a multimeter, even if they appear intact. Check for proper amperage ratings and fuse type specifications.

Slow-blow fuses can develop high resistance before completely failing, causing voltage drops.

Check Protection Device Coordination

Verify that all protection devices are properly coordinated and sized for the machine's power requirements, including inrush current handling.

Perform Insulation Resistance Test

Use a megohmmeter to test insulation resistance of all motor windings, power cables, and major electrical components. Minimum 1 megohm to ground.

Disconnect all electronic components before performing insulation testing to prevent damage.

Check Ground Fault Circuit Interrupter

If equipped with GFCI protection, test the device operation and check sensitivity settings. Verify it's not nuisance tripping due to normal leakage current.

VFDs and servo drives can generate normal leakage currents that may cause sensitive GFCIs to trip.

Inspect Cable Routing and Condition

Examine all power cables for physical damage, proper routing away from sharp edges, and adequate strain relief at connection points.

Pay special attention to cables in cable tracks or areas with frequent movement.

Verify Grounding System Integrity

Check continuity and resistance of the machine grounding system, including cabinet grounds, motor grounds, and safety ground connections.

Access TNC Diagnostic Functions

Enter MOD function and navigate to the power supply diagnostic screens to check real-time voltage readings and power fail status indicators.

Compare TNC internal voltage readings with external multimeter measurements to identify monitoring circuit issues.

Check Power Fail Detection Circuit

Locate the power fail detection circuit board (typically near the power supply) and inspect for damaged components, loose connections, or corrosion.

This circuit operates at line voltage - ensure proper safety procedures.

Verify TNC Software Configuration

Check if any power management parameters or voltage monitoring thresholds have been modified in the TNC configuration that could cause false alarms.

Consult the machine builder's documentation for any custom power monitoring settings.

Test with Known Good Power Supply

If possible, temporarily connect a known good power supply to isolate whether the issue is with the supply itself or the TNC monitoring circuit.