Technical Resources & Knowledge Base

Is it the supply, the input power, or a short downstream? Step 1: Visual & Smell Check • Smell: A strong "burnt electronics" smell usually indicates a blown capacitor or MOS-FET. The unit is likely dead. • Visual: Look for charred marks, bulging capacitors, or a blown internal fuse (if visible). • LED Status: Is the "DC OK" or "Power" LED on? If it's off or blinking, proceed to testing. Step 2: Check Input Voltage (Source) • Set your multimeter to AC Volts. • Measure across the input terminals (L and N, or L1/L2/L3). • Result: You should see your standard facility voltage (e.g., 120VAC, 240VAC, 480VAC). • If 0V: The problem is upstream (breaker, fuse, or wiring to the panel). Step 3: Check Output Voltage (Load Disconnected) • Crucial Step: Turn off power, disconnect the output wires (+V and -V), and then turn power back on. You must test it "unloaded" to rule out a short circuit in your machine dragging the voltage down. • Set multimeter to DC Volts. Measure across the output terminals. • Result: You should see a steady voltage (e.g., 24VDC). • If voltage is bouncing or 0V: The power supply is dead. • If voltage is steady: The power supply is good; you have a short circuit in a sensor, valve, or wire downstream.

Is the "brain" dead or just confused? Step 1: Check Status LEDs • Power LED: If off, check the power supply feeding the PLC (see above). • RUN Light: Should be solid Green. If flashing, it may be in program mode or stopped. • FAULT / SF (System Fault) Light: • Flashing Red: Often a recoverable error (battery low, I/O mismatch, memory card missing). Try power cycling. • Solid Red: Usually a fatal hardware error or "watchdog timer" fault. The CPU may be dead. Step 2: Isolate the CPU • If the power supply is good but the PLC won't power up (or stays in fault), power down and remove all I/O modules. • Power up with just the Power Supply and CPU. • If it boots up: One of your I/O cards is faulty and dragging down the backplane. Add them back one by one to find the bad one. • If it still fails: The CPU or rack/chassis is faulty. Step 3: Communication Basics • Ping Test: Can you "ping" the PLC IP address from a laptop? • Port Check: Look at the Ethernet port. Are the Link/Activity lights blinking? No lights usually means a bad cable, dead switch port, or dead PLC port.

Is it the drive, the motor, or the mechanical load? Step 1: Check the Display/Fault Codes • Most drives have a display. A blank display (with good input power) usually means the internal power supply is blown. • Common Codes: • Overcurrent: Often a short in the motor or cable. • Overvoltage: Often a regeneration issue (braking too fast) or input power spike. • Feedback Error: The cable connecting the motor encoder to the drive is loose or broken. Step 2: The "Disconnect" Test (For Overcurrent Faults) • If the drive trips immediately upon enable: • Power down and disconnect the motor cables (U, V, W) from the drive. • Power up and try to enable the drive. • If it still trips: The drive is blown (shorted internal IGBTs). • If it does NOT trip: The drive is likely fine; the problem is in the motor or the power cables running to the motor. Step 3: Mechanical Binding Check • With power off, try to turn the motor shaft by hand (if it doesn't have a brake). • If it won't turn, your machine is mechanically jammed. The servo drive is just doing its job by tripping out to save the motor.

Why isn't the machine seeing the part? Step 1: The "Wrench Test" (Inductive Proximity Sensors) • Hold a metal object (wrench/screwdriver) in front of the sensor face. • Does the light on the sensor body turn on? • No Light: Check the cable for breaks. If 24V is present at the connector but no light, the sensor is dead. • Light turns on but PLC doesn't see it: The sensor is switching, but the signal isn't reaching the PLC. The break is in the wire running back to the panel, or the PLC input card is dead. Step 2: Cleanliness Check (Photoeyes) • 90% of photoelectric sensor failures are just dirty lenses. Wipe them off with a clean cloth. • Check alignment: Is the reflector bent or knocked out of position?

Is the screen broken or is the system frozen? Step 1: The Flashlight Test (Black Screen) • If the screen is black but the power light is on: Shine a flashlight at an angle against the glass. • If you can faintly see the graphics: The Backlight has failed. The HMI brain is fine, but it needs a repair (bulb/inverter replacement). • If it is pitch black: The LCD or internal power board has failed. Step 2: Touch Responsiveness • If the touch is off-center, look for a "Calibration" menu in the system settings (usually accessed by holding a corner of the screen during boot-up). • If one specific area never works (dead spot), the Digitizer (glass touch overlay) is physically damaged and needs replacement.

Is the fuse actually blown, or is it something else? Step 1: Visual Inspection • Glass fuses: Look for a broken filament or black scorch marks inside. • Ceramic/Industrial fuses: You usually can't see inside. Do not rely on visual checks alone. Step 2: Continuity Test (Power OFF) • Remove the fuse from the holder (crucial to avoid false readings). • Set multimeter to Continuity/Ohms (Ω). • Touch probes to ends of the fuse. • Result: It should beep or show near 0.0 Ohms. • If it shows OL (Open Line) or no beep: The fuse is blown. Step 3: Voltage Drop Test (Power ON - Advanced) • If you cannot remove the fuse, measure Voltage across the fuse terminals while the circuit is live. • Result: You should read 0V across a good fuse (electricity flows through it, no potential difference). • If you read full voltage (e.g., 24V or 120V) across the fuse: The fuse is blown (it is acting as an open switch).

Why isn't the air/fluid turning on? Step 1: The Magnetic Test • With the solenoid powered ON, hold a steel screwdriver tip near the top of the coil stem. • Result: You should feel a magnetic pull. • No pull: The coil is not energized (check wiring) or the coil is burnt out (open circuit). Step 2: Resistance Check • Turn power off and disconnect the plug/wires from the coil. • Measure Resistance (Ohms) across the coil pins. • Result: You should see a specific resistance value (check manufacturer specs, usually 20-100 Ohms). • If OL (Open): The internal winding is broken. Replace the coil. • If 0.0 Ohms: Short circuit. This likely blew your fuse or PLC output card.

The PLC light is on, but the motor starter isn't engaging. Step 1: The "Click" Test • Toggle the input signal. Can you hear or feel the relay "click"? • No Click: The coil isn't getting power or is burnt out. • Click heard, but nothing happens: The contacts are likely pitted, carbon-covered, or welded. Step 2: Inspect the Contacts • Look through the clear plastic case. Are the contacts black or melted? • If they look okay, perform a continuity test across the Normally Open (NO) contacts while manually pushing the actuator button (if equipped).

The motor stopped and the drive is dark. Step 1: Check Incoming Power • Measure Phase-to-Phase voltage at the drive input terminals (L1, L2, L3). • Result: Should be balanced (e.g., 480V across all legs). If one leg is dead (0V), you have a blown main fuse or tripped breaker upstream ("single-phasing"). Step 2: Check the DC Bus • If the display is blank but input AC is good, the internal DC power supply might be dead. • Measure DC Voltage at the DC Bus terminals (+ and -). • Result: Should be roughly 1.41 x AC Input Voltage (e.g., ~678VDC for a 480VAC input). • If 0V or very low: The drive's pre-charge circuit or rectifier is blown.

Why is my temperature reading "9999" or "Error"? Step 1: Check for "Open Wire" • Most controllers display a high-limit error if the sensor breaks. • Disconnect the thermocouple from the controller. • Measure Resistance (Ohms) across the two wires. • Result: Should be low resistance (a few Ohms). • If OL (Open Line): The sensor tip is broken internally. Replace the probe. Step 2: The "Jumper" Test (Controller Check) • If the sensor tests fine, jumper the two input terminals on the temperature controller with a piece of wire. • Result: The display should read "Ambient Temperature" (room temp). • If it still says Error: The controller input card is faulty.

Is it the cable or the port? Step 1: Continuity & Shorts • For Serial (DB9) or simple cables, use a multimeter to check continuity from pin to pin. • Also check for shorts between pins (e.g., Pin 2 touching Pin 3). Step 2: The "Wiggle" Test • With the system running, gently wiggle the connector at the device end. • If communication drops out or lights flicker, the solder joints on the device's port or the crimp on the cable are bad.

The machine won't reset. Step 1: Cycle the E-Stops • Push and pull every E-Stop button on the line. Sometimes a contact block comes loose on the back of the button. Step 2: Check Contact Blocks • Safety circuits are "Normally Closed" (NC). They open when you hit the button. • With power off, measure continuity across the contact block on the back of the button. • Result: With the button out (run position), you should have continuity. • If Open (OL): The contact block is broken mechanically.

The coil pulls in, but the motor doesn't run. Step 1: Check Voltage Through the Contacts • With the contactor engaged (pulled in), measure voltage across the top and bottom of each pole (L1 to T1). • Result: Should be near 0V (indicating a closed switch). • If you measure full voltage (e.g. 480V): The contact is burnt out inside and not conducting electricity. Step 2: Smell Check • A distinct "burnt plastic" smell usually means the coil has overheated and melted the casing, preventing movement.

The sensor light is on, but the PLC doesn't see it. Step 1: Identify PNP vs NPN • PNP (Sourcing): Sends +24V to the PLC when active. • NPN (Sinking): Sends 0V (Ground) to the PLC when active. Step 2: Measure at the PLC Card • Place your black meter probe on 0V (Common). Place red probe on the PLC input screw terminal. • Trigger the sensor. • Result (PNP): Meter should jump from 0V to 24V. • If 0V stays 0V: There is a break in the wire between the sensor and the PLC.

Is it tripped or failed? Step 1: Check the Handle Position • ON: Up/Right. • OFF: Down/Left. • TRIPPED: Floating in the middle / loose feel. • To Reset: You must firmly push it fully to OFF before you can push it to ON. Step 2: Voltage Drop Check • With breaker ON, measure voltage from the Line side (Top) to the Load side (Bottom) of the same pole. • Result: Should be 0V. • If you measure voltage (e.g. 120V): The internal contacts are burnt open, even if the handle says "ON." Replace the breaker.