Introduction

Many electronic problems appear to be software or communication issues.

Examples:

 

• • MCU does not start

• • Communication errors

• • Random reset

• • Sensor malfunction

• • Flash programming failure

• • Industrial controller stop

• • Vision system error

However, in many cases, the root cause is:

Power quality problem

Before replacing ICs or changing software, engineers should first verify:

 

• • Input power

• • Regulator output

• • VCC stability

• • Ripple

• • Ground

• • Reset signal

This article explains a practical troubleshooting method used in real engineering projects.

Step 1. Define the Symptom

Before measuring, clearly identify the problem.

Example:

Symptom	Possible Cause
MCU not booting	Reset issue
Random reset	VCC drop
Communication failure	Noise
ADC error	Ground noise
Flash write failure	Power instability
Sensor malfunction	Voltage drop

Do not start by replacing parts.

Start by asking:

“When does the problem happen?”

Examples:

 

• • During startup?

• • During motor operation?

• • During communication?

• • During high current?

• • During temperature changes?

Step 2. Follow the Power Path

Always trace the power flow.

Example:

   24V Input
      ↓
   Fuse
      ↓
   Protection Circuit
      ↓
   DC/DC Converter
     ↓
   5V
     ↓
   LDO
     ↓
   3.3V
     ↓
   MCU

Measure every point.

Example:

Point	Voltage
Input	24.2V
DC/DC Output	5.05V
LDO Output	3.30V
MCU Pin	3.15V

Problem:

         3.30V−3.15V=0.15V3.30V – 3.15V = 0.15V

You found:

Voltage drop.

Step 3. Measure During Real Operation

Many systems work correctly at idle.

Problems occur during:

 

• • Motor start

• • Relay ON

• • Communication

• • Vision processing

• • High CPU load

• • Flash programming

Example:

Condition	VCC
Idle	3.30V
Communication	3.25V
Peak Load	3.05V

If MCU minimum voltage:VMIN=3.0VV_{MIN}=3.0V

This is dangerous.

Step 4. Use an Oscilloscope

Multimeter:

  3.30V

Oscilloscope:

  3.30V
    ~~~~~~~

Possible findings:

   Ripple

     ~~~~~~~~~~

   Spike

     -----|
          |
          |----

   Voltage Sag

     ------
           \____

   Ringing

     ---/\/\/\---

Oscilloscope measurements reveal problems invisible to multimeters.

Step 5. Check Reset Signal

A stable reset is critical.

Example:

   Power ON
         ↓
   Reset Low
         ↓
   VCC Stable
         ↓
   Reset Release
        ↓
   MCU Start

Bad case:

   Power ON
          ↓
   VCC unstable
          ↓
   Reset unstable
          ↓
   Boot failure

Real-World Engineering Experience

During development of a controller board, startup problems occurred occasionally.

Measurements found:

 

• • Power instability

• • Unstable reset timing

• • Undefined boot signal state

Solutions:

✔ Reset circuit modification

✔ Pull-up resistor addition

✔ Boot signal improvement

Result:

Stable startup.

Step 6. Check Ground

Many engineers measure only VCC.

Ground is equally important.

Example:

   MCU
    │
    │
   GND
    │
    │
   Connector

High current: 

    V = IR

Even ground can move.

This creates:

 

• • Communication errors

• • ADC errors

• • Noise

• • Reset problems

Always check:

Local Ground

Not only:

System Ground

Step 7. Check Decoupling Capacitors

Incorrect:

   MCU ---------------- 100nF

Better:

   MCU --100nF

Checklist:

✔ Correct value

✔ Close placement

✔ Short ground

✔ Good vias

Step 8. Compare Good vs Bad Board

This is a powerful method.

Example:

Parameter	Good	Bad
VCC	3.30V	3.10V
Ripple	20mV	100mV
Reset	Stable	Unstable
Startup	OK	Failure

Differences often reveal the problem quickly.

Step 9. Use Thermal Inspection

Heat often indicates problems.

Check:

 

• • Regulators

• • MOSFETs

• • Connectors

• • Power ICs

Example:

   Normal:40°C

   Abnormal:85°C

Possible causes:

 

• • Overload

• • Short circuit

• • Bad solder

• • Poor cooling

Thermal cameras can help.

Step 10. Troubleshooting Flow

   Problem
      ↓
   Define Symptom
      ↓
   Check Input Power
      ↓
   Measure VCC
      ↓
   Check Ripple
      ↓
   Check Reset
      ↓
   Check Ground
      ↓
   Check Capacitors
      ↓
   Check Load
      ↓
   Compare Good Board
      ↓
   Find Root Cause

Industrial Example

Example system:

   UPS
    ↓
   24V
    ↓
   Power Supply
    ↓
   PLC
    ↓
   Industrial PC
    ↓
   Network
    ↓
   Vision System

Problem:

Vision system stops randomly.

Investigation:

✓ Input power OK

✓ Network OK

✓ Software OK

Found:

 

• • Ripple increased

• • UPS battery degraded

• • Power quality poor

After replacing UPS battery:

System became stable.

This shows:

Good power quality improves system reliability.

Common Mistakes

Replacing ICs without measurement

Ignoring ground

Measuring only idle condition

Long oscilloscope ground wire

Ignoring reset circuit

Ignoring connector resistance

Ignoring temperature effects

Engineering Troubleshooting Rule

Good engineers do not start with:

“Which component is broken?”

They start with:

“What changed?”

Then measure:

 

• • Voltage

• • Current

• • Temperature

• • Signal

• • Timing

This approach saves time and reduces unnecessary component replacement.

Final Thoughts

Most intermittent PCB problems are related to:

 

• • Power

• • Ground

• • Reset

• • Noise

• • Timing

A practical engineering approach is:

   Measure
      ↓
   Observe
      ↓
   Analyze
      ↓
   Verify
      ↓
     Fix

This troubleshooting method is useful for:

 

• • Industrial controllers

• • PLC systems

• • Communication equipment

• • Vision systems

• • Automotive electronics

• • Medical devices

• • Embedded systems

 

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• • Best Oscilloscopes for Electronics Engineers: Personal Use vs. Professional Lab Equipment – PowerTechGuide