How do I test for a short circuit?

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MacBook Air 13インチ Retina 2020

2020年3月に発売されたインテルプロセッサ搭載MacBook AirモデルA2179の2020年リフレッシュモデルの修理・分解情報です。

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Fire Aussie @fireaussie

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投稿日: 2023年8月22日

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How do I test for a short circuit?

I’ve got a faulty MacBook Air as listed the device. Its screen is non-functional as it is severely damaged. The MacBook boots to the Apple Logo ( I test and found this out by plugging a display cable into an adapter to the Mac), it then just sits there and the fans spin and cpu gets really hot. I’ve tried dfu restore and revive and nothing seems to work. I can target disk mode and sometimes alt choose disk but nothing seems to load. It was fine before this happened and I had taken the screen off.

I am just wondering how should I test for a short circuit somewhere on the board? As I’m wanting to learn what has caused it. I’ve got a multimeter and that’s basically it haha.. Just wanting to know.. Thanks

The multimeter I have.

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Uh I know it’s going to cost a lot to fix. I’d still like to know how to diagnose

Fire Aussie さんによる2023年8月25日

How long are you letting it sit trying to boot? What sort of error do you get when you do the DFU restore? I

When you say the CPU gets hot, have you checked? Or is the fan just spinning at full speed?

I know your question was about checking for shorts. I'll get there if need be :)

Alisha C さんによる2023年8月25日

@flannelist About an hour and a half is the maximum I’ve tried letting it boot (sits on apple logo). I don’t get an error when doing DFU restore, it was successful supposedly.

CPU physically gets hot AND fans spin at full speed.

Have I added that there is no screen attached as it is severely damaged? It might of shorted the computer once but computer worked after I removed the screen

Fire Aussie さんによる2023年8月25日

@fireaussie You did not, but I would have inferred something of that sort anyhow, based on the mention of screen damage. But the confirmation helps.

Was there any other damage? Did it do the same thing before you disconnected the screen (but after it was damaged)

Alisha C さんによる2023年8月26日

@flannelist all good. With the information provided, what now?

Fire Aussie さんによる2023年8月26日

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Fire Aussie @fireaussie

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投稿日: 2024年5月7日

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I eventually sold this laptop to a buyer on eBay. I had messaged the buyer and he said all that was wrong with it, was the screen. He put in a new screen and everything worked ok. He had to DFU restore before putting macOS on it. Weird that the computer wouldn’t boot because no screen attached.

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Uh I know it’s going to cost a lot to fix. I’d still like to know how to diagnose — Fire Aussie
How long are you letting it sit trying to boot? What sort of error do you get when you do the DFU restore? I

When you say the CPU gets hot, have you checked? Or is the fan just spinning at full speed?

I know your question was about checking for shorts. I'll get there if need be :) — Alisha C
@flannelist About an hour and a half is the maximum I’ve tried letting it boot (sits on apple logo). I don’t get an error when doing DFU restore, it was successful supposedly.

CPU physically gets hot AND fans spin at full speed.

Have I added that there is no screen attached as it is severely damaged? It might of shorted the computer once but computer worked after I removed the screen — Fire Aussie
@fireaussie You did not, but I would have inferred something of that sort anyhow, based on the mention of screen damage. But the confirmation helps.

Was there any other damage? Did it do the same thing before you disconnected the screen (but after it was damaged) — Alisha C
@flannelist all good. With the information provided, what now? — Fire Aussie

Alisha C @flannelist 評価: 37.8千 28 42 36 · Answer 1 · 2023-08-27T08:15:05-07:00

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Alisha C @flannelist

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投稿日: 2023年8月27日

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Couple things I would try if you haven't yet. Do an NVRAM reset. That resets boot information, so if there's some weird boot nonsense stuck somewhere, that should clear it.

It could be you do have a short, or some component is just getting super hot now, so the device is legitimately throttling to protect itself from overheating. But I still would want to try a few things first before jumping to that.

If not, this sounds similar to what happens when a Mac is missing sensor data. Typically this relates to the battery or the trackpad, but in theory, it's possible a missing display could also do this. I feel like I have seen it before, but my memory isn't 100%. What happens if you run diagnostics? Press and hold D at power on, just like you would for any other start up keyboard combo (target disk, startup disk, etc...).

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Hi I am very apologetic for the late response. I’ve tried an NVRAM reset and no success. It doesn’t do the Apple logo twice as mentioned in the guide.

The cpu is getting insanely hot really quick though.

The trackpad and battery are confirmed to be plugged in. The screen is not and really can’t be plugged in as it may short the system or damage somehow. The screen is really not in a good place!!

Running diagnostics doesn’t work either, the Apple logo still shows and CPU gets insanely hot.

I have a manual multimeter available if needed.

Again, apologies in the long delay.

Fire Aussie さんによる2023年11月11日

Sorry @flannelist still looking for an answer

Fire Aussie さんによる2023年11月17日

@fireaussie Do you have a schematic, or boardview? Or a USB C style multimeter/ammeter? (something like this)?

To test for shorts you don't really need them, but it does help. Honestly before assuming this might be a board problem, I would want to confirm there's nothing wrong with any of the other parts. What happens if you disconnect everything and then try to power on? (You can connect a display or external monitor, or the fan just so you have so info to go on). You may still get heavy fan spin, but the CPU shouldn't actually be getting hot if it's in protection mode (i fsensor data is missing).

Alisha C さんによる2023年11月19日

Hi @flannelist , No I don’t have a schematic and I guess boardview? I don’t have a USB-C multimeter . And that’s what I’ve been been doing if you’re talking about accessories. What do you want me to try and disconnect? The display is already disconnected and I’m only connecting to the external display, did you want the battery disconnected too? Touchpad? What else?

Fire Aussie さんによる2023年11月22日

@flannelist I have updated OP with the multimeter I have

Fire Aussie さんによる2023年11月22日

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