if my incoming power supply exceeds 240v, could this prevent my imac from powering up

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Level 1

4 points

if my incoming power supply exceeds 240v, could this prevent my imac from powering up

My 2017 years iMac has an intermittent fault whereby it will not power up. If I leave it for a while (days or weeks) and then try again, it will suddenly start up and run perfectly. I have taken it to my local repair centre for investigation which I also did a few years ago for the same reason. No fault was found and it was OK for a short while, which was probably coincidental. Whilst doing some electrical work at home I discover that my incoming voltage is 245+. I was wondering if the incoming supply voltage at this level would prevent the iMac from powering up. Either that or is there an intermittent fault with the power supply.

iMac 27″ 5K, macOS 13.5

Posted on Sep 13, 2023 5:40 AM

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Answer 1

Old Toad

Level 10

217,276 points

Sep 13, 2023 11:01 AM in response to Tawads

The next time it won't power up unplug the power cord from the back of the Mac for about 15 seconds. Plug it back in and try the power button again. It it powers up right away that's an indication of a failing power supply. I went thru the same thing with a 2014 iMac.

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Answer 2

ku4hx

Level 7

23,746 points

Sep 13, 2023 5:58 AM in response to Tawads

If it's been working on "245+" then I doubt that's a cause. Higher than expected voltage is not something a device can just "get used to". If the voltage were too high, the Mac would have failed early on.

You can't just guess about voltages. Devices are built to use a certain range of voltage and it takes a device such as a multimeter or volt/amp meter to determine exactly what line's electrical conditions are.

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Answer 3

BDAqua

Level 10

251,131 points

Sep 13, 2023 6:00 AM in response to Tawads

5% over or under should not matter...

https://forums.mikeholt.com/threads/acceptable-voltage-variations.17047/

That'd be 228 to 252 .

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Answer 4

BDAqua

Level 10

251,131 points

Sep 18, 2023 12:14 PM in response to Tawads

Nothing else connected to it that wasn't connected at the store?

Like even an ethernet cable???

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Answer 5

Tawads Author

Level 1

4 points

Sep 13, 2023 6:31 AM in response to ku4hx

I have also looked at power supply company advised range which is 230v -6% +10% or 216-253v, which doesn’t really fit with products designs to run between 220 and 240v.

If the power is the problem, then I guess the best thing I can do is to install a UPS/regulator to run it through which will give a constant 220v output?

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Answer 6

Tawads Author

Level 1

4 points

Sep 13, 2023 6:21 AM in response to Tawads

I have just tested the incoming supply and currently have voltage reading of 248.5 which is clearly high. I haven’t seen any other issues with equipment, but perhaps the iMac is much more sensitive to higher voltage?

When it did start a few days ago, I managed to update everything to latest versions and took a look at the built in diagnostics which said everything was OK, but I guess if everything started up, it would say that.

it might be that when the voltage dips, it starts and when it’s elevated it doesn’t?

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Answer 7

Tawads Author

Level 1

4 points

Sep 18, 2023 10:17 AM in response to Tawads

Well I now have my iMac back and going with the thought of high voltage being the cause of my issue, I invested in a voltage regulator. Having tried to turn it on prior to running through the regulator, I got nothing. Plugged it in via the regulator set to 230v, I thought I was in business when I heard the chime. Then came the increasing noise of the fan ramping up, but sadly a black screen remained along with the never before heard rather loud and annoying noise of the fan. I then went through all of the Apple suggested attempts to remedy the fault. I’m now at a loss and other than taking it back to the iStore repair guys I do t know what to do. If anyone has any other suggestions I would welcome them before resorting to the second visit in a week to the repair guys who incidentally couldn’t get it to fail although had clearly had the screen off at one point during their investigation.

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