Lab: Display Diagnostics Bench
Diagnose real display faults: gather evidence, test your theory, apply the right fix, verify the result
A Isolation Techniques (Objective 5.4)
Tests that isolate the real cause
- 1External display test. Connect a known-good external monitor. If it works, the internal panel/cable/backlight is suspect, not the GPU or motherboard.
- 2Flashlight test. Shine a flashlight at an angle on a "dim" screen. An image underneath means the backlight/inverter has failed, not the panel.
- 3Full-screen color-cycle test. Cycle solid red/green/blue/white. Dots that stay fixed on every color are dead (stuck off) or stuck (stuck on) sub-pixels, not content.
- 4Input-source check. "No Signal" means the display has power but is not receiving the right data on the selected port.
Why the order matters
- 1A fix chosen before you isolate the cause is a guess. Replacing a panel when the fault is a cable wastes a teardown.
- 2A theory that ignores the evidence you gathered is still a guess, even if it sounds technical.
- 3Testing separates a real cause from a plausible-sounding one. A disconfirmed theory sends you back to Theory, not forward to a fix.
- 4The repair should directly address the CONFIRMED cause.
- 5Never call a fault resolved until you have verified the display end to end.
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B Live Display View Reported symptom
C Diagnose the Fault
1. Investigate
2. Theory
3. Test
4. Repair
5. Verify
Step 1: Investigate
Gather evidence before you guess. Run at least 2 checks, then continue.
Findings
No findings yet.
Step 2: Establish a Theory
Pick a theory. It must be grounded in evidence you actually gathered; a theory is locked until its evidence is on the board.
Step 3: Test the Theory
Run the test before you touch anything. A disconfirmed theory sends you back to Step 2.
Step 4: Repair
Pick the fix that addresses the CONFIRMED cause. A fix that does not match the cause solves nothing.
Step 5: Verify + Prevent Recurrence
Pick a real preventive measure, then verify the display is fully resolved.
Exam Tip