Industrial Electronics 101: How Basic Testing and Measurements Are Done

Who this guide is for

If a machine stopped unexpectedly or behaves “on and off,” this article explains how professionals start testing—in plain language. You’ll learn what to check safely, what tools help, and what to send us if you want a board-level evaluation.

Safety first (please read)

• Disconnect mains and wait for DC bus capacitors to discharge.

• Use lockout/tagout where applicable.

• If you are not trained to work on live equipment, do not energize it—collect the info listed below and contact us.

Essential tools (minimal kit)

• Digital multimeter (DMM) with continuity/diode modes

• Clamp meter (optional, for current)

• Insulation resistance tester (a.k.a. megohmmeter) if motors/cables are involved

• Bench power supply with current limit (helpful for low-voltage sections)

• Infrared thermometer or small thermal camera (optional)

• Good lighting + magnifier; ESD strap and mat

Step 1 — Quick facts you should collect

• Machine/drive brand & model, board part numbers, firmware labels

• Symptoms & when they occur (startup, under load, after warm-up)

• Any error codes or LED blink patterns

• Recent changes: power outages, water/chemical exposure, wiring work

Tip: Photos help a lot—front/back of the board and the connector area.

Step 2 — Visual inspection (no power)

Look, don’t touch yet:

• Burn marks, cracked/bulged capacitors, discolored resistors

• Green/white deposits around connectors (corrosion)

• Loose heat-sinks, broken headers, rubbed cables

• Smell test: a sharp/acidic smell may indicate electrolytic or burnt parts

If you see any of the above, stop here and document with photos.

Step 3 — Basic measurements (power OFF)

1. Continuity & fuses:

   • Check input fuses/thermistors with the DMM’s continuity mode.

   • Open circuit = likely blown; replace only after root cause is known.

2. Diode test on the rectifier / MOSFETs / IGBTs:

   • Use diode mode between device pins. You should read a forward drop (~0.3–0.8 V) one way and open the other way.

   • 0.00 V both ways → shorted device. Open both ways on a rectifier leg → likely faulty.

3. Resistance to ground:

   • Measure between DC bus (or supply rail) and ground/chassis.

   • A few kilo-ohms that rise slowly can be normal (capacitors charging). A solid low value (e.g., <10 Ω) suggests a short.

4. Insulation resistance (if motors/cables):

   • With a megger at 500–1000 V, check motor windings to ground and phase-to-phase.

   • Healthy systems often read >100 MΩ to ground (exact limits vary by motor/standard).

If any reading is suspicious, do not power the system again—contact us.

Step 4 — Safe power-on checks (only if trained)

If the above looks normal and you are qualified:

1. Soft start / current limit:

   • Use a bench current-limited supply for low-voltage sections (e.g., 24 V), or a variac/isolation + series bulb for AC (only by trained personnel).

2. Check logic rails:

   • Verify 5 V (±5%), 3.3 V (±5%), 12 V (±10%), ±15 V if applicable.

   • Rails that drop under load or oscillate often point to bad capacitors or regulators.

3. Ripple on DC bus (quick check):

   • On the multimeter AC mode across the DC bus capacitors, ripple should be small versus the DC level (rule-of-thumb <5–10%).

   • High ripple = dried electrolytics or rectifier issues.

4. Temperature scan (non-contact):

   • After 2–3 minutes, scan heat-sinks, inductors, and regulator ICs.

   • Unusual hot spots (far above neighbors) signal localized faults.

Oscilloscope users: gate drive to MOSFET/IGBT is typically 10–15 Vpp; irregular or missing drive points to driver/feedback faults. Use proper grounding or differential probes.

Step 5 — Decide & document

Make a short test log:

• What passed/failed

• Photos of the board and measurement points

• Any readings that looked abnormal

If anything is unclear, stop further testing. Re-powering with an unknown short can destroy the board and increase repair cost.

What to send us for a faster evaluation

When you contact PCB Tech USA, please include:

• Brand/model & board part numbers

• Error codes and when they appear

• What you measured (bulleted notes are fine)

• Photos: front/back and connector close-ups

• How the unit is used (duty cycle, environment, e.g., humidity/heat)

Ship-in service available: We offer free pre-diagnosis for shipped boards. If a repair is not feasible, we can quote new/refurb alternatives and apply any paid diagnosis toward the replacement.

FAQ (quick)

Do I need an oscilloscope?No. A DMM covers the basics. If we need scope captures, we’ll guide you.

I can’t power the machine safely.Don’t. Send the board with your notes—safer and usually cheaper.

How long does evaluation take?Initial feedback is typically fast once we receive the board and details above.

Print-friendly checklist

1. Collect model/part numbers & symptoms

2. Visual check → photos

3. Power-off tests: fuses, diode test, ground resistance, insulation (if motor)

4. (If trained) Power-on: rails, ripple, temps

5. Stop if abnormal → contact PCB Tech USA with your notes