Lesson 5: Hardware, Video, and Projector Fault Isolation

Core path: 42 minutes

Week 4 ends with systems that all look "broken."

They are not broken in the same way.

Your job is to stop using the symptom as the diagnosis.

Ticket A: completely dead

Evidence:

• no LEDs;
• no fans;
• no display;
• known-good outlet.

Build the next three checks without opening the PSU.

Possible boundaries include external power, PSU switch/input state, motherboard power, front-panel switch wiring, PSU failure, or board failure.

Ticket B: starts, then shuts down under load

Evidence:

• boots normally;
• idle use is stable;
• temperatures climb under load;
• CPU fan speed is abnormal or absent.

State the strongest hypothesis, one alternative, and the safest next check.

Ticket C: burning smell or unsafe electrical evidence

Evidence:

• user reports burning smell from the system;
• system was recently under high load.

Do not power it on again to reproduce the smell. Stop normal service and escalate under the approved hardware-safety procedure.

Ticket D: new GPU, no display

Evidence:

• system powers on;
• GPU installed;
• monitor and cable test good elsewhere;
• GPU supplemental power requirement is not yet verified.

Do not reinstall the operating system. Stay near the failed boundary.

Display and projector tickets

Ticket E: monitor says no signal

Evidence:

• PC appears to boot;
• monitor has HDMI and DisplayPort inputs;
• cable is connected by DisplayPort;
• monitor is manually selected to HDMI.

Diagnosis starts with incorrect input source.

Ticket F: projector image is fuzzy and too large

Possible evidence to inspect:

• projector focus;
• projector-to-screen distance/zoom;
• source resolution and aspect ratio;
• digital scaling;
• cabling/signal quality.

Do not replace the GPU because the projected image is the wrong size.

Ticket G: projector is dim and shuts down intermittently

Possible boundaries include:

• aging/burnt-out lamp where the projector uses a replaceable bulb;
• blocked airflow/filter;
• overheating;
• power issue;
• brightness/eco settings.

Intermittent shutdown plus high internal temperature/blocked vents is different evidence from a simple wrong input.

Ticket H: dead pixels vs burn-in

Dead pixels are individual pixels that fail to operate normally.

Burn-in/image retention is persistent image-pattern damage/retention behavior associated with some display technologies and usage patterns.

They are different symptom classes and may have different service outcomes.

Ticket I: flashing or distorted image

Check:

• cable/connector seating and known-good cable;
• refresh-rate/resolution compatibility;
• GPU/driver state;
• display input capability;
• panel/display hardware evidence.

A flashing image is not automatically a bad monitor.

Ticket J: wrong colors or missing audio

For incorrect color:

• inspect cable/interface;
• display color/settings/profile;
• GPU/driver state;
• panel fault evidence.

For missing audio over HDMI/DisplayPort:

• verify the selected audio output device;
• confirm the interface/monitor supports audio;
• check mute/volume and driver state.

Symptom checklist

By the end of this challenge, you should have encountered all major A+ display/projector symptom categories:

• incorrect input source;
• physical cabling issue;
• burnt-out bulb;
• fuzzy image;
• burn-in;
• dead pixels;
• flashing screen;
• incorrect color;
• audio issue;
• dim image;
• intermittent projector shutdown;
• sizing issue;
• distorted image.

Build the service record

For three tickets, document:

Symptom:

Known-good evidence:

Last proven-good boundary:

Strongest current theory:

Alternative theory:

Controlled next check:

Safety boundary:

Expected result if theory is correct:

Verification after repair:

Unit 1 technician defense

Use one scenario to explain the complete reasoning chain:

safe service
→ identify hardware/display technology
→ verify compatibility
→ trace power/data/video paths
→ observe firmware/POST
→ isolate the fault
→ verify
→ document

Final checkpoint

Before moving to mobile devices, you should be able to defend these statements:

• A component can physically fit and still be incompatible.
• A device can be installed and still lack required power.
• Heat management is part of system reliability.
• Burning smell is a stop-work safety condition.
• A black screen has multiple possible boundaries.
• Display technology and display signal path are different troubleshooting layers.
• Projector symptoms require projector-specific evidence.
• Troubleshooting means narrowing evidence, not swapping random parts.