things
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identify things on the board
- power supplies
- bios chips
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reset bios: unplug bios battery for 30s
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don’t check random things (beginner mistake)
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shorted Cap … most common fault
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follow the power
- start with power plug
- after maybe some mainboard protection circuits … it should go (0ohmms) to every power supply on the board and be 19v (it’s the main power rail)
- then there is always a 19v to 5v and to 3.3V converter → the 5v and 3.3v power rails
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when you give power to a laptop mainboard, without battery and not turned on → there should be almost no current
- so when it draws eg: 160mA → too much
- a mosfet or cap, when it’s shorted is short → full current would flow and not just 160mA ~100Ohm
- also if a cap to gnd somewhere takes 160mA the board should still work
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on laptops you often have two 3.3v rails: one for high amp and one for not
- the low power one goes to the SIO = Super Input Output Chip or EC = Embedded Controller
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there are often quite some caps around the SIO = Super Input Output Chip