What is the SW4 button?

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Dell XPS 15 9560

Dell XPS 15 9560은 2017년에 출시된 고성능 경량 노트북으로, 4K 해상도의 15.6인치 슬림 베젤 스크린과 7세대 Intel Core i3-7100H 프로세서를 탑재하고 있습니다.

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Eyal @eyal34026

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게시됨: 2025년 4월 3일

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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:

View from the bottom:

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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oldturkey03 @oldturkey03 평판: 858k 1.4k 972 2.4k · Answer 1 · 2025-04-03T21:32:14-07:00

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oldturkey03 @oldturkey03

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

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.

Eyal 의 2025년 4월 3일

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SMASHED IT @smashedit 평판: 1.3k SMASHED IT, Auckland 12 4 · Answer 2 · 2025-04-03T23:18:15-07:00

SMASHED IT @smashedit

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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.

Eyal 의 2025년 4월 3일

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).

Eyal 의 2025년 4월 4일

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Dell XPS 15 9560

What is the SW4 button?

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