Fans are blowing at full power in sleep mode only

Question

MacBook Pro 15インチ Touch Bar Late 2016

Appleの2016年ラップトップラインアップの最新モデルは、プロフェッショナルユーザーを対象としています。 15インチ、2880 x 1800 Retinaディスプレイ、クアッドコアIntel Core i7、256 GB / 512 GB / 1 TB / 2TBストレージオプション、16 GB RAM、およびTouch Barを搭載したキーボードです。

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Thomas Toffalori @thomastoffalori

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投稿日: 2020年1月13日

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Fans are blowing at full power in sleep mode only

Dear Community,

I hope you have more ideas than me and you can help me with this :-)

Once my Macbook goes into sleep mode, either through closing the lid or by clicking on sleep on the apple menu at the top left corner, the behavior is as follows:

After closing the lid it takes around 20 seconds until the MacBook really goes into sleep mode. You can hear that, because the first 20 seconds the fans are blowing slowly, probably to cool the cpu down before going into sleep mode.
After this, you can hear that the fans stop and the Mac really goes into sleep mode, but right after the fans start blowing at full power and never stop (even after two days)
The fans work perfectly fine while using the mac. Even controlling the fan speed using a dedicated sofware work perfectly fine.

Things I tried:

SMC Reset (several times)
PRAM Reset
Boot into Safe mode
Complete reinstall of the OS
Running Hardware Diagnostic: Showed no errors

Things I noticed:

Even if I close the lid on the user profile selection screen (right after boot, before logging on) it happens
After the Hardware Diagnostic you can boot into a “special” safe mode, where you can only sent the diagnostic results to apple. And it happens even there.
The instant I connect the power chord, while in sleep mode, the fans stop.

After all of this, I assume it really is a hardware issue. Do you think I can fix it myself? Or what would you do? Unfortunately the MacBook is already out of warranty.

Thanks for your support!

Thomas

@vhanzl Thanks again for your help. Unfortunately cleaning did no help. Here you can find a picture:

https://imgur.com/a/AtMtENd

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I'd hypothesize that SMC controls fan via PWM, switching signal line between ON and OFF. When SMC itself goes to sleep (say those 20 secs after closing the lid), it leaves this signal in a default state which should be OFF but is ON instead due to some minor hardware fault. There might be big pulldown (or pullup) resistor on FET gate and due to disconnected resistor or partial breakage of the FET or dirty board surrounding these (dirt acting like resistor pulling the signal wrong way), signal defaults to ON instead. Maybe you could first try cleaning the board around the place where the fan is connected and send us photos of it if cleaning itself does not help? We might spot that FET which I imagine and hint you more what to measure or try.

Vaclav Hanzl さんによる2020年1月23日

Hi Vaclav, thank you very very much for your suggestion. I will try it and get back to you once I know more :-)

Thomas Toffalori さんによる2020年1月24日

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I'd hypothesize that SMC controls fan via PWM, switching signal line between ON and OFF. When SMC itself goes to sleep (say those 20 secs after closing the lid), it leaves this signal in a default state which should be OFF but is ON instead due to some minor hardware fault. There might be big pulldown (or pullup) resistor on FET gate and due to disconnected resistor or partial breakage of the FET or dirty board surrounding these (dirt acting like resistor pulling the signal wrong way), signal defaults to ON instead. Maybe you could first try cleaning the board around the place where the fan is connected and send us photos of it if cleaning itself does not help? We might spot that FET which I imagine and hint you more what to measure or try. — Vaclav Hanzl
Hi Vaclav, thank you very very much for your suggestion. I will try it and get back to you once I know more :-) — Thomas Toffalori

Dan @danj 評価: 478.9千 Self employed contract worker 35 329 970 · Answer 1 · 2020-02-01T07:24:26-07:00

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Dan @danj

評価: 478.9千

Self employed contract worker

35

329

970

投稿日: 2020年2月1日

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@Thomas Toffalori - Unlike the newer 2018 model which have a T2 chip, yours doesn’t offer this so you do have a means to easily boot up under an external drive.

I would see if the problem is still present when you are running off of the external. Create a bootable external drive with the same OS version you are currently using.

Using the Option key when you start your system you’ll gain access to the Boot Manager to select the external drive.

Let us know if that made a difference!

Reference: Mac startup key combinations

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Hi Dan, thanks fo your suggestion. I just tried it, but unfortunately booting from an external drive did not help. Do you have any other ideas? :-)

Thomas Toffalori さんによる2020年2月1日

OK, that removes an OS, or virus/malware or app issue!

Lets check one more thing... Install this gem of an app: CoconutBattery and paste a snapshot of the main window here so we can see what's happening with your battery and charger. We need two snapshots one with the battery charged and the second after your system has gone to sleep with the racing fan before you've plugged in your power adapter again.

Dan さんによる2020年2月1日

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MacBook Pro 15インチ Touch Bar Late 2016

Fans are blowing at full power in sleep mode only

Update (01/13/2020)

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