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Why is my laptop not powering on?

Yoga C740-15IML Laptop power button stays on for 8 seconds and goes off for 8 seconds.

This problem started as an intermittent shutdown problem. Lenovo hardware diagnostics did not identify a problem. Windows 11 has been reinstalled and the drivers updated from both the Lenovo site and the Intel website. Seemed to be good for over 24 hours and then it shut down again.

In the past I was able to power it up after the unexpected shutdowns but now it just stays off with the power button lighting for 8 seconds, off for 8 seconds.

Removing the power, battery and holding down the power button for 30 seconds turns it off but it goes back to the power button 8 second loop again when it is powered on.

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Hi Kevin,

Yeesh, sounds like an ugly problem. Have you verified the AC adapter is putting out the correct voltage for your laptop? That would be my first step to check that with a voltmeter. After that I'd open up the case and measure the voltage on the DC input jack's pins to verify the power is actually getting to the motherboard.

If everything is good up to that point, then I'd seriously start to consider whether a new battery might be called for. Yeah, it's only three years old, but depending on usage the battery could well be starting to fail. That's really about all that's left at this point that's fixable without board-level repairs, so that's what I'd try myself.

The batteries aren't particularly cheap, but they're not outrageously expensive either; the ones I saw were running from about $50-60 USD. Here's one of the first examples I came across.

Lenovo Yoga C740 YOGA C740-15 Yoga C740-15IML Replacement Battery: BatteryClerk.com

iFixit unfortunately doesn't have a guide available for replacing the battery, but given that you've stated you've unplugged the battery I assume you know how to go about replacing it.

Good luck with it; let us know what happens!

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Hi Jerry W,

I haven't been able to verify if the AC adapter is putting out the correct voltage. It uses a USB C connector, and I don't have a clue how to test it without a USB tester.

I'm unable to find info on how to test the USB C DC input jack's pins to verify the power at that end.

It is getting power to the motherboard. The power light goes on when I plug in the power adapter, and I have used my multimeter to test various components on the motherboard. I don't know what the voltages of the various components should be so I can't confirm that the power supply is putting out the correct voltage.

I ran the laptop on the battery for about 6 hours yesterday so I'm not sure that that is the problem. It charged normally after that. I also tested the battery with my multimeter and it's putting out 12.3 volts. It's labeled as a 11.52V 5080MAh battery. I'm not sure why there is a discrepancy.

I'll keep looking for a way to test the power supply and the motherboard voltages.

Thanks for your help,

@reardo

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Kevin Reardon sera éternellement reconnaissant.
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