Troubleshooting guides
Practical diagnostic sequences for the faults that actually stop production — written and reviewed by a working maintenance professional, not a textbook. Each guide pairs with a hands-on module in the trainer.
The fastest PLC troubleshooting move is to connect, go online, and read what the controller actually sees — instead of guessing and swapping parts. The code doesn't lie.
Training module · PLC trackSometimes the controller is the problem, not the machine. Read the processor and module status LEDs, the fault code, and comms to know in seconds whether to chase the field or the PLC.
Training module · PLC trackForcing an I/O point can isolate a field fault from a logic fault in seconds — and can hurt someone if you use it wrong. The discipline that keeps forcing a tool, not a hazard.
Training module · PLC trackThe same circuit is drawn three ways for three questions. The ladder shows the logic, the wiring diagram shows the physical terminals, the one-line shows the power. Reach for the right one.
Training module · Prints trackWith the print as your map, a voltmeter finds the one open device in a control rung in a couple of readings — no bypassing protection, no guessing. Read, don't jumper.
Training module · Prints trackField changes, added jumpers, swapped terminals, the wrong revision — sometimes the drawing describes a machine that no longer exists. Spot the disagreement, trust the panel, prove it, red-line it.
Training module · Prints trackNew training module. A dead output is a trail of breadcrumbs — go online, find the rung, and trace the false condition backward to the real cause. The code doesn’t lie. Six hands-on scenarios.
PLC track · training moduleCompare the field device to the PLC input tag, and the output tag to the actuator — and you cut a machine fault down to one link before you touch a tool.
Training module · PLC trackWhen the false condition is an internal bit instead of a physical input, the cross-reference names the exact rung that writes it — and the trail always ends at a real device.
Training module · PLC trackWhen a machine starts and instantly drops out, or won't shut off no matter what, the fault is in the holding logic — read the seal-in or the latch and it shows what's keeping it on or off.
Training module · PLC trackA step that times out is usually a confirmation that never arrived. Read the timer's accumulated value against its preset and a 'random fault' becomes a specific missing signal.
Training module · PLC trackWhen one trip sets off a cascade of alarms, the loudest is rarely the cause. First-out and sequence-of-events capture which fault came first — so you fix the trigger, not the pile-on.
Training module · PLC trackYou'll rarely troubleshoot code you wrote. Walk into a strange program, trace one dead output backward, and reverse-engineer the designer's intent — fast, under pressure.
Training module · PLC trackBefore you trace one wire, read the legend, title block, and sheet index — so you never trace the wrong revision with the wrong symbol meanings.
Training module · Prints trackA wire number is a street address for a conductor. Learn the scheme, read the terminal strip, and put your meter on the exact wire the print names — every time.
Training module · Prints trackA relay coil in one spot can operate contacts scattered across the whole print set. The cross-reference lists every one, and whether it's NO or NC — so the contact three sheets over never ambushes you.
Training module · Prints trackA print draws every contact de-energized and at rest — often the opposite of how it sits running. Read the as-drawn state, then picture the operating state, and a 'closed' contact that's really open stops fooling you.
Training module · Prints trackThe control circuit tells the contactor to close — the power side is where the motor gets its three phases. Read disconnect, fuses, contactor, and overload in order and a dead motor gives up its cause fast.
Training module · Prints trackA machine that 'won't start' is usually one open link in the control string — a blown control fuse, an E-stop in the chain, or a single missing permissive. Read the string and the open link stands out.
Training module · Prints trackField device to terminal to I/O point to PLC tag — read the I/O drawing and you can walk a signal from copper to code and find exactly where it breaks.
Training module · Prints trackA true story. A pump that wouldn't run, a crew that had “tried everything,” and the loudest clue in the building — hidden on purpose, one breaker reset at a time.
The Callout · true storyA true story. A tech spent an hour on a drive that wasn't even in the circuit — and the fault was the part he'd just installed himself.
The Callout · true storyA true story. A new PowerFlex drive, a crew that answered in one voice — and the one jumper they all missed.
The Callout · true storyA true story. They replaced a pull-cord, chased the whole circuit for two hours — and the box they'd just bolted on was sitting tripped.
The Callout · true storyThe honest one. After a power outage I asked if the PLC comm cables were right, took their word for it — and lost four hours to it.
The Callout · true storyA hot bearing is a symptom with three very different causes. Read temperature, vibration, and noise together to find the real one.
Bearings · reliabilityThe overload relay is a messenger, not the culprit. The three phase currents tell you which of three faults you actually have.
Motors · electricalWhen a level, flow, or pressure reading looks wrong, the loop current tells you whether to chase the process or the instrument.
InstrumentationTrace the E-stop, gate, and light-curtain string by voltage to find the open device — without ever bypassing the protection.
Safety circuitsMisalignment gets misdiagnosed as imbalance constantly. One reading tells them apart — and points at what keeps pulling it out.
Alignment · couplingsThree failures in one spot isn't a bad batch — it's a force that shouldn't be there. How to read the failed bearing and find it.
Bearings · reliabilitySwapping parts until the machine runs feels productive. It's one of the most expensive habits in a maintenance department — here's why.
The case for troubleshootingThe fault code names the symptom, not the cause. Here's the sequence to find the real root of overload and overcurrent trips.
VFD · drivesA motor only has three ways to get too hot. Each leaves a different fingerprint — learn to read it before replacing anything.
MotorsStarving, worn, cavitating, or fighting a restriction? Two gauge readings and a walk down the pipe tell you which.
PumpsThe sensor is usually the honest one in the story. Here's how to tell whether it's telling the truth.
Sensors · PLCThe cylinder is rarely the fault. Walk the air chain from supply to actuator in the right order.
PneumaticsPump, relief valve, or cylinder? A gauge in the right spot localizes the loss without a teardown.
HydraulicsDoes the fault follow the belt or stay put? That one question routes you to the real cause.
ConveyorsDirection and frequency turn "it's vibrating" into a specific named fault — often before any teardown.
VibrationTwo worlds inside one device. Measure the coil voltage first, then inspect the contacts.
ControlsA stable loop that went unstable is a "what changed" problem, not a "what should the gains be" problem.
Control loopsEvery guide here pairs with a hands-on module in faultline101, where the readings respond to your choices and you diagnose faults on equipment you can't break. Module 1 is free.
Works with no signal. Install it on your phone and the whole course — 35 modules, 210 faults — comes with you into the plant.
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