EC standby: always-on rails present but power button does nothing

English EC-path guide for “3V/5V ALW OK, button dead” (paraphrased community teaching theme; NLCRC rewrite). What must be true before S0 - EC VCC present and out of reset. - Power-button debounce into the EC (or a matrix sense) actually toggling. - EC firmware / SPI content intact enough to run the power sequence. Method 1) Confirm ALW rails and EC clock/crystal. 2) Scope or meter the button signal at the EC pin while pressing. 3) Watch for PWRBTN# / EC_RSMRST# / enable lines that should change — if ALW exists but enables never move, stay on the EC side before blaming CPU VRMs. Firmware caution - Do not mass-erase EC flash without a verified dump for that board revision. - Some boards share SPI with BIOS; wrong clip work bricks both. Include EC part marking, ALW voltages, and whether the charge LED reacts to the button.