SescoTech Computers

Case Study: Laptop Power Issue Diagnosis & Repair

Today, I received a laptop with a power issue. The system would turn on but then shut down immediately. To diagnose the problem, I followed the power sequence step by step:

1. Checked the Charging IC requirements – Everything was fine.

2. Examined the Step Down section – No issues found.

3. Verified the IO requirements – All signals were present.

4. Checked the System Power OK signal – It was intact.

5. Analyzed the PLT_RST and CPU Reset signals – Both were fine.

6. Checked the DRAM Power Good signal – It was working.

7. Identified a missing RAM Reset signal – The required 1.35V on pin 30 was absent.

Tracing the Issue

I traced the signal path and found that the SOC chip was outputting the signal correctly to a resistor, and the signal was also passing through the resistor. However, it wasn’t reaching the RAM slot. Interestingly, there was no short circuit on that line.

Since this was unusual, I suspected a PCB trace issue. Upon close inspection under a microscope, I found a very minor break in a track. This break was preventing the signal from reaching the RAM slot.

Repair Process

1. Cleaned the broken track thoroughly.

2. Cut the track completely to ensure a clean repair.

3. Created a new connection using a jumper wire.

4. Rechecked the circuit to confirm continuity.

After completing the repair, I powered on the laptop, and it successfully booted with a display.

Conclusion: The issue was a broken PCB trace affecting the RAM reset signal. By carefully diagnosing and repairing the broken connection, I was able to restore the laptop’s functionality.

This case highlights the importance of meticulous circuit tracing and deep analysis using a microscope when dealing with power sequence failures.

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