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Module 09ProfessionalWeek 9 · 19 min read

Diagnostics & Error-Code Analysis

Stop guessing. Start reading the device.

Module 9 of 1267%
01

Welcome

Welcome to Module 9. Professional technicians are separated from hobbyists by one habit: they diagnose before they act. This module builds that discipline into a repeatable process.

02

Learning Objectives

  • Run a structured intake diagnostic.
  • Separate hardware from software symptoms.
  • Read kernel panics and bootloader messages.
  • Estimate repair time and success probability.
  • Know when to stop and refer.
03

Prerequisite Knowledge

  • Advanced level complete

If any of these are unfamiliar, review the Foundation level first.

04

Vocabulary

Kernel panic
A fatal kernel error that halts or restarts the device.
Bootloop counter
A device counter that triggers fallback after repeated failures.
Intake test
The standard check performed before accepting any device.
Reproduction
Reliably triggering the fault so you can confirm the fix.
05

Why This Matters

A twenty-minute structured diagnostic protects you from three hours of unpaid work and from accepting jobs that cannot be completed.

06

Lesson Content

Lesson 1The intake protocol6 min

Photograph the device. Record IMEI, model, visible damage, and whether it powers on. Ask three questions: what happened, when, and what was already tried elsewhere.

'What was already tried' prevents you inheriting someone else's failed flash without knowing it.

Lesson 2Hardware or software?7 min

Software faults are reproducible and usually stage-consistent — the device always dies at the same point. Hardware faults drift: they change with temperature, pressure or charge level.

If a device behaves differently when warm, stop treating it as a software fault.

Lesson 3Reading failures6 min

Capture logcat, dmesg where available, and the exact wording of any bootloader message. Search the exact string, not a paraphrase.

07

Visual Explanation

Symptom described
      ▼
 Reproduce it
      ▼
 Isolate the stage (BootROM / BL / kernel / OS)
      ▼
 Non-destructive tests
      ▼
 Hypothesis + expected fix
      ▼
 Act, then verify
Diagnostic funnel
08

Real-World Example

A customer says: “It works fine, then dies after ten minutes and won't restart until it cools.”

Software or hardware?

Hardware — thermal behaviour is not a firmware symptom.

Possible causes

  • Failing NAND
  • PMIC fault
  • Liquid damage corrosion
09

Technician Tips

Technician Tip

Always reproduce the fault before repairing it, and after.

Technician Tip

Log the intake state with photos; it protects you in disputes.

Did You Know?

Roughly a third of devices brought in for 'software problems' have liquid damage indicators already triggered.

10

Common Mistakes

Common Mistakes

  • Flashing before diagnosing
  • Accepting a device without an intake record
  • Not verifying with a soak test
11

Safety Notice

Safety Notice

  • Disclose the possibility of unrecoverable data loss before accepting the job.
  • Never promise a fix you have not diagnosed.
12

Hands-on Practice

Exercise 9 — Intake three devices

  1. Perform a full intake on three real devices
  2. Classify each fault by stage
  3. Write a predicted repair path and confidence level for each
13

Knowledge Check

Question 1 of 2

A fault that changes with temperature is most likely:

14

Mini Project

Mini Project — Intake form

  1. Design a one-page intake form
  2. Include IMEI, condition, consent and prior-work fields
  3. Use it on five real jobs and refine it
15

Reflection

  • Which step do you skip when busy?
  • What did that cost you?
16

Module Summary

Today you learned:

  • Intake protocol
  • Hardware vs software
  • Log reading
  • Reproduce-verify discipline
17

Resources

18

Assignment

Document three real diagnostics end to end, including the evidence that supported each conclusion.

20

Module Test

Complete the 2-question knowledge check above plus the assignment. Passing score: 80%.