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The Dell XPS 15 9560 is a light weight, high-performance laptop released in 2017 that features a thin-bezel 15.6-inch screen with 4k resolution and a 7th Generation Intel Core i3-7100H.

What is the SW4 button?

While researching a problem(*) I noticed that on the back of the mainboard, just next to the battery, there is a momentary switch with "SW4" in white next to it.

It can be barely seen from the top - see pictures

View from the top:

Block Image

View from the bottom:

Block Image

There is no access to the switch from either the kb or the bottom.

(*) An aside: coffee was spilt on it, it died, it was given to me. I got it going (much cleaning) and now it says "AC not connected". BTW there is no battery.

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@eyal34026 that is a service mode switch for updating the Flash memory region.

Block Image

Unlikely that this is your problem. You will need to check the main power rail since it tells you that it does not detect the AC connection.

To troubleshoot the power issue, you might want to use the Dell XPS 15 9560 LA E331P Schematic

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Thanks, this clarifies it for me.

Regarding my main issue, I will try to trace through the schematics.

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This is the service mode switch, which is typically not necessary for common issues like yours. It is mainly used when formatting the ROM or cleaning the mE region for BIOS purposes. It's unlikely that this is related to the problem you're trying to resolve. If your laptop is not detecting AC power, check the Vbus_AC detector and the DCIN_ACOK. Also, verify the power around the BQ24777, including VCC, ACDET, and ACOK. Additionally, inspect PQ304 and PR327

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Thanks, will do.

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Moving on... Looking at the "Vbus_AC Detector", at PU202A/B I see both are 3.1V. These are the DCIN_ACOK and VBUS_ACOK. So are these active H (OK) or active L (NOK)? Need to think more.

This was with power supplied but the machine not started.

Now with the machine actually running I see 0V on pin 1 (VBUS_ACOK). Still 3.2V on pin 7 (DCIN_ACOK).

[later] BQ24777 is a b#$%y small chip but I managed to find a fine probe and measured ACOK at 1.1V. Don't know what it should be.

Anyway, since this is the battery charger, and there is nobattery installed, can it really lead to "AC not installed"?

Aside: Since the laptop does boot and work, power is delivered so the full path is likely good. It is only the status that the BIOS shows which has "AC not installed", and this stops fw update (but this can be forced).

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