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newSchoolWorks.com › VoTechWorks › Manufacturing & Marine › Robotics / Mechatronics › Troubleshooting Mechatronic and Robotic Systems › Lesson 12
MFG-MECH15-07 · Lesson 12 · 12 clock hours · lab

Comprehensive Troubleshooting Practicum and Capstone Review

Objective. Students will independently diagnose and repair three randomly assigned faults drawn from all course subsystems (electrical, PLC, pneumatic, drive, robot) within a time limit, producing complete work orders for each fault.

⚠ Pending professional review

This lesson, its worked examples and its practice questions has not yet been verified by a licensed engineer or certified journey-level tradesperson or by a certification or approval body. It is a study draft and may contain errors. Do not use it as instructions for work on a job site or on live equipment. Always follow your instructor, your supervising professional, and current official references and regulations.

VoTechWorks program approval and accreditation are still in progress. Credentials are issued only by the certifying bodies named in each program, after their own exams.

Comprehensive Troubleshooting Practicum and Capstone Review

Why This Lab Matters

This practicum is the culminating lab of the course. You will work independently, with no coaching, to diagnose and repair three real faults drawn from the full range of subsystems you have studied: electrical/sensor, PLC or drive, and robot or pneumatic. The goal mirrors what an electro-mechanical or mechatronics technician does every shift — you must identify the root cause, isolate energy safely, make the repair, verify the fix, and document everything on a work order. Employers and credentialing bodies (FANUC, Siemens, PMMI) all expect this complete cycle.

The Seven-Step Troubleshooting Process

Every fault attempt should follow the same disciplined sequence:

1. Observe and define the problem — What symptom is reported? What is the machine doing or not doing?

2. Gather information — Review fault codes, indicator lights, HMI alarms, previous work orders.

3. Identify possible causes — List hypotheses from most likely to least likely.

4. Write a test plan — State the first three tests you will run and the tools you need. This is the 10-minute planning step before you touch any equipment.

5. Test and isolate — Execute tests one at a time, eliminating causes.

6. Repair and verify — Make the fix, restore energy, run the machine, confirm normal operation.

7. Document — Complete the work order immediately while details are fresh. Then write your self-assessment.

The planning step is not optional. Technicians who skip it spend more time chasing the wrong cause and create more downtime.

Safety Before Every Fault Attempt

Lockout/tagout (LOTO) is not negotiable. Any time you must expose yourself to hazardous energy — electrical, pneumatic, hydraulic, or stored mechanical — you apply LOTO per OSHA 29 CFR 1910.147. The procedure is: shut down the machine, isolate every energy source, apply your personal lock and tag, release or restrain stored energy, and verify with a meter or pressure gauge that energy is at zero before you work. In this lab, a critical LOTO deviation on any fault attempt results in an immediate stop and a failing mark for that fault — no exceptions.

For electrical work, follow NFPA 70E: verify absence of voltage with a calibrated meter (test the meter on a known live source first, test the circuit, test the meter again). Wear the PPE appropriate to the arc-flash and shock boundaries for the panel you are working in.

For robot faults, the robot must be in a stopped state with the teach pendant in T1 or T2 mode when you enter the work envelope, consistent with ANSI/RIA R15.06 / ISO 10218 safeguarding requirements. Never bypass or defeat a safety gate or light curtain.

For pneumatic faults, exhaust system pressure and verify zero pressure at the component before disconnecting fittings. Flying fittings and unexpected actuator movement are the primary hazards.

Machine guarding (OSHA 1910.212) must be replaced before you restore power and run a verification cycle.

Electrical and Sensor Fault Strategy

Common electrical/sensor faults include open circuits, short circuits, failed sensors (inductive, capacitive, photoelectric), and loose or corroded terminals. Use your multimeter in the correct mode — resistance for continuity checks with energy isolated; DC voltage or AC voltage with energy present (observe all NFPA 70E requirements). Check sensor supply voltage first, then signal output, then wiring back to the I/O card. A 4–20 mA loop fault can produce a zero reading (open wire) or a full-scale reading; scale your expected milliamp value using the formula: mA = [(PV – PV_min) / (PV_max – PV_min)] × 16 + 4.

PLC and Drive Fault Strategy

For PLC faults, go online with your programming laptop and watch the ladder logic in real time. A rung that should be true but is false tells you which input or internal coil is the problem. Check the I/O status table: is the physical signal present but the PLC not seeing it? That is a wiring or card issue. Is the PLC seeing the input but the output not energizing? Check the output image table and any interlock logic. For drive faults, read the fault code on the drive display, look up the code in the drive manual, check DC bus voltage, check motor current, and check the feedback device (encoder or resolver). Always clear faults after the root cause is fixed, not before.

Robot Fault Strategy

FANUC robot faults appear as ALARM codes on the teach pendant. Use the ALARM LOG to read the active and history faults. Common student-level faults include position errors (SRVO-023), I/O signal faults, and frame errors that cause the robot to move to an unexpected position. Check that tool frame and user frame numbers loaded in the active program match the physical setup. Use ROBOGUIDE concepts to visualize what the program expects. After any repair, jog the robot to a safe position, run the program in T1 mode step-by-step before switching to automatic.

Work Order and Self-Assessment

Your work order must include: machine ID, fault symptom as reported, date and time, tests performed and results, root cause identified, corrective action taken, parts used, verification result, and your signature. Incomplete work orders fail on documentation even if the repair was correct. The self-assessment asks which of the seven steps took longest and what you would change. This reflection is a professional habit that improves your speed on future calls.

Passing Standard

You must correctly identify the root cause and complete the repair on at least 2 of your 3 faults within the allotted time, with zero critical LOTO deviations across all attempts, and earn an aggregate rubric score of at least 80% across all three work orders.

Key terms9

Root causeThe single underlying failure that, when corrected, eliminates the fault symptom; distinguishable from symptoms, which are the observable effects of the root cause.
Lockout/tagout (LOTO)The energy-isolation procedure required by OSHA 29 CFR 1910.147 that physically locks energy sources in the off position and verifies zero energy before any worker contacts hazardous equipment.
Fault codeA numeric or alphanumeric alarm displayed by a PLC, drive, or robot controller that identifies the category and cause of a detected error condition.
Verify absence of voltageAn NFPA 70E-required step in which a technician uses a calibrated meter (tested on a known live source before and after) to confirm that no voltage is present at a circuit before working on it.
Work orderThe formal written record of a maintenance action, including the reported symptom, tests performed, root cause, corrective action, parts used, and verification that the machine returned to normal operation.
4–20 mA loopAn industry-standard analog signal circuit where 4 mA represents the minimum process value and 20 mA represents the maximum; an open circuit reads 0 mA, a useful diagnostic indicator.
ANSI/RIA R15.06 / ISO 10218The industrial robot safety standard specifying safeguarding requirements, safe working modes (T1, T2, automatic), and collaborative operation boundaries for robot work envelopes.
Teach pendant T1 modeA reduced-speed manual operating mode on FANUC and other industrial robots in which the robot moves only while a deadman (enabling) switch is held, limiting speed to allow safe programming and fault investigation inside the work envelope.
Seven-step troubleshooting processA structured diagnostic sequence — observe, gather information, identify possible causes, plan tests, test and isolate, repair and verify, document — used to find root causes efficiently and safely.

Worked examples4

1. A 4–20 mA pressure transmitter on a pneumatic circuit is scaled 0–150 psi. The PLC analog input module displays a raw milliamp reading of 12 mA. What is the current process pressure, and is the sensor in the normal operating range for a system set at 90 psi?
  1. Write the 4–20 mA scaling formula: PV = [(mA – 4) / 16] × (PV_max – PV_min) + PV_min
  2. Substitute values: PV = [(12 – 4) / 16] × (150 – 0) + 0
  3. Simplify: PV = [8 / 16] × 150 = 0.5 × 150 = 75 psi
  4. Compare to setpoint: the system is set at 90 psi; the transmitter reads 75 psi, which is 15 psi low. This warrants investigation of actual system pressure with a mechanical gauge to determine whether the transmitter is mis-calibrated or the system pressure is genuinely low.
Answer: The current process pressure indicated is 75 psi, which is 15 psi below the 90 psi setpoint. The sensor signal itself (12 mA) is within the valid 4–20 mA range, so the signal wire is intact; the next step is to cross-check with a calibrated mechanical gauge.
2. A FANUC robot stops with a position error alarm. Before the fault, the tool frame was changed. The tool is a gripper with a TCP offset of 150 mm in the Z direction from the flange. If the tool frame Z entry was accidentally entered as 15 mm instead of 150 mm, how far off will the programmed TCP position be from the actual TCP position?
  1. Identify the error: the entered Z offset is 15 mm; the correct Z offset is 150 mm.
  2. Calculate the difference: 150 mm – 15 mm = 135 mm.
  3. Interpret: the controller believes the TCP is 135 mm closer to the flange than it actually is, so every taught position will place the real TCP 135 mm past the intended target in the tool Z direction.
Answer: The TCP will be offset by 135 mm from every taught position. The repair is to correct the tool frame Z entry to 150 mm and re-verify or re-teach all affected program points.
3. A double-acting pneumatic cylinder with a bore diameter of 2 inches needs to extend against a load. Shop air pressure is regulated to 80 psi. What is the maximum theoretical extension force the cylinder can produce?
  1. Calculate the piston area: Area = π × r² = π × (1 in)² = π × 1 = 3.1416 in²
  2. Apply the cylinder force formula: Force = Pressure × Area = 80 psi × 3.1416 in²
  3. Calculate: Force = 251.3 lb (rounded to 251 lb)
Answer: The maximum theoretical extension force is approximately 251 lb. Actual force will be less due to seal friction and pressure losses; if this is insufficient for the load, the remedy is to increase pressure (within component ratings) or use a larger bore cylinder.
4. During a PLC fault, an online ladder diagram shows that an output coil (conveyor motor starter) is de-energized. Rung logic shows three normally-open contacts in series: Sensor_A (I:0/0), Guard_OK (I:0/1), and Timer_T1_DN (T4:1/DN). The I/O status table shows I:0/0 = 1 (ON), I:0/1 = 1 (ON), and T4:1/DN = 0 (OFF). The timer T4:1 has a preset of 5 seconds and an accumulated value of 0. What is the most likely root cause and what is the next test?
  1. Evaluate each contact: Sensor_A = ON (passes), Guard_OK = ON (passes), Timer_T1_DN = OFF (blocks the rung).
  2. The output is de-energized because the timer done bit is not set. The timer accumulated value is 0, meaning the timer has not started or has been reset.
  3. Find the timer coil rung: locate the rung in the program that energizes timer T4:1 and check whether its enable conditions are met.
  4. Most likely root cause: the timer enable rung is not being satisfied, so the timer never accumulates. The next test is to go online, find the T4:1 timer coil rung, and identify which contact in that rung is false.
Answer: The root cause is that timer T4:1 is not running because its enable rung conditions are not met. The conveyor output is correctly blocked by logic — this is not a wiring fault. The technician must trace upstream to the timer enable rung and find the unsatisfied condition there.

The math in this lesson2

Learners scale a 12 mA reading to psi on a 0–150 psi transmitter.
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Brush up in the math halls at newSchoolWorks.com:
In class: Fault draw and planning: each student draws three fault-scenario cards (one electrical/sensor, one PLC or drive, one robot or pneumatic) and has 10 minutes to write a brief test plan for each before touching any equipment, listing the first three tests they will perform and the tools required. · Timed independent fault-resolution lab: students execute their three repairs on the integrated training cell or individual stations; the clock runs from the moment they touch equipment; instructor observes but does not coach; LOTO must be applied correctly each time energy isolation is required or the fault attempt is stopped and marked as failed. · Work-order submission and self-assessment: after completing each repair, students complete the work order immediately and then complete a written self-assessment identifying which step in the seven-step process took longest and what they would do differently; instructor reviews and scores all three work orders and the self-assessment before the final exam.
Materials: Integrated training cell, fault-scenario cards (instructor prepared, at least 15 unique faults), LOTO equipment, full PPE set, multimeter, pressure gauge, PLC programming laptop, teach pendant, work-order forms, timer
Check: Three graded work orders: student must correctly identify the root cause and complete the repair on at least 2 of 3 faults within the allotted time, with zero critical LOTO deviations on any fault attempt; 80% aggregate rubric score across all three work orders required to pass.

Practice check8

Answer each question, then check it. Nothing is recorded; this is your own practice.

Electrical Safety / NFPA 70E
1. During the capstone practicum, a student begins removing a terminal block cover on a control panel without first verifying absence of voltage. Under NFPA 70E, what is the correct action the student should have taken immediately before removing the cover?
FANUC CERT — Robot Troubleshooting
2. A student's fault-scenario card describes a FANUC robot that stops with a position error alarm shortly after a tool change was performed. The first step in the seven-step troubleshooting process is to observe and define the problem. What information should the student gather in step 2 before forming hypotheses?
PMMI Mechatronics — Fluid Power
3. A pneumatic cylinder with a 3-inch bore is supplied at 100 psi. Using the formula Force = Pressure × Area, what is the approximate maximum extension force? (Use π ≈ 3.1416.)
PMMI Mechatronics — Programmable Logic Controllers
4. In online ladder logic monitoring, an output coil is de-energized. Three series contacts in the rung all appear closed (highlighted) on the PLC programmer software. What is the most likely reason the output is still OFF?
Safety — LOTO / OSHA 29 CFR 1910.147
5. According to OSHA 29 CFR 1910.147, which sequence correctly describes the steps for applying lockout before working on a machine with both electrical and stored pneumatic energy?
Siemens SMSCP / PMMI Mechatronics — Electrical Components and Sensors
6. A 4–20 mA temperature transmitter is scaled 0–200 °F. The PLC reads 8 mA from the transmitter. What is the indicated temperature?
FANUC CERT / Robot Safety — ANSI/RIA R15.06
7. During the robot fault portion of the capstone, a student needs to enter the robot work envelope to inspect a tooling mount. The safeguarding gate is closed. Under ANSI/RIA R15.06 / ISO 10218, which condition must be met before the student opens the gate and enters?
Troubleshooting Methodology — All Credentials
8. A student's self-assessment after the capstone states: 'Step 4 (writing the test plan) took longest because I listed every possible cause instead of ranking them by likelihood.' What is the primary benefit of ranking hypotheses from most likely to least likely before testing?
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