English triage flow for “dead” or “no power” laptops.
1) Upstream
- Adapter voltage under load, DC jack path, charge IC enable, battery pack communication if the design requires it.
2) Always-on vs switched
- Separate always-present rails (often 3VALW / 5VALW) from S0 rails that only appear after EC/PCH handshake.
- Missing always-on rails → start at adapter/charge/protection. Missing S0 only → look at EC, power button, and enable signals.
3) Short isolation
- Resistance-to-ground on the dead rail. Very low ohms → inject carefully or lift suspects (MOSFET, ceramic pack, IC).
- Use BoardView to see everything hanging on that net.
4) Sequencing
- Many boards need EC ready + PCH power good before CPU VRMs fire. Capture enables with a scope or logic if voltages look “half alive”.
Document rail names from the schematic of the matching revision — names differ across ODMs.
Power rails
Power rail triage: 3V/5V, enables, and sequencing
Board: Laptop power rails · 25 views · Solved
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