Model A1224 / Mitte 2007 und Anfang 2008 / 2, 2.4, oder 2.66 GHz Core 2 Duo Prozessor

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Power Supply drop at 120vac in

This machine runs fine with 122-123volts AC in.

With normal 120volts AC, internal and external USB-powered HDD's fail.

I assume the power supply is failing.

What is the experience with this? A particular capacitor or caps (as in G5's) or other component?

Or should I just replace the PSU?

Update (11/29/2016)

Hi Mayer, to clarify: At 120vac the internal HDD fails, and the external, USB3 HDD backup fails as well.

Additional info: About a year ago, after 2 years of service, at 120vac, the external HDD failed. I suspected voltage drop across the connectors joining a 2M USB extension cable to the short USB2/USB3 cable shipped with the HDD. I replaced the 2-part cable with a single 2m USB2/USB3 cable and all was well for a year. I did not measure voltages at that time.

So evidently power drop has progressed since then.

BTW, I also got my Apple II in '79. Quickly got another one for my office. Interfaced it with my Telex machine. Then got my secretary into word processing on it.

Beantwortet! View the answer Ich habe das gleiche Problem

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Are you saying internal and external SATA drives? There are no internal USB powered drives.


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Gewählte Lösung

To start with I would strongly recommend getting a good UPS for your system as its sounds like your AC power is not very stable.

The power supply offers power at different voltages across your system. Its possible the 5 Volt rail your USB ports offer to your external drive may have a problem (as well as causing your internal HD issues).

A useful tool here is a USB power meter like this one: AboveTek which you can see whats happening without opening you system as well as check your USB devices.

Most likely your power supply has issues as to fixing it Vs replacing. I would just replace it as it's just easer and safer. Here's the IFIXIT guide: iMac Intel 20" EMC 2133 and 2210 Power Supply Replacement.

Update (12/01/2016)

Yes, your power supply offers other voltages as well as multiple feeds of some. Your internal HD has access to 3.3 and 12 volts feeds as well as 5 volts I spoke about before.

Here's a good diagram which lists the power lines. The power pin's (3 per) are carrying the same voltage feed each.

Block Image

As you stated your external drive was having a problem the USB ports offer only 5 volts which is why I suspected the 5 volt rail was having problems.

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Thanks Dan. Don't be distracted by why my place operates at 122-123vac. The normal home for this machine operates at 120. When I first realized it was working at my place, and not in its normal place, I suspected recent construction at the normal place was at fault. And that nothing was wrong with the iMac. Turns out to be the reverse.

I assume the internal HDD requires more than +5vdc. Is that correct?

My limited experience since '79 is that the fault is most often switches or PSU's. I did look at the Guide before my posting.


You'd be surprised even in a newly build building can have power issues, often because the lines feeding your building are in sad shape. Here in Boston some locations the voltage is as low as 92!, In other locations as high as 130.

In the cities I think is worse than urban areas. But, even in the farmlands lightning or line failures can be a big issue.

We use UPS's on all of our desktop systems and good surge suppressors for our laptops. A good UPS offers a power meter which can help you monitor your power as well as ground voltages if present.

Running a system with to low or to high a voltage is not healthy for the system as it over taxes the power supply as it needs to off set the difference.


Thanks Dan. My place has had a PV system for a year and a half or so. New entrance panel, net meter, etc. The inverter appears to be the source of the over voltage. Its panel displays 122/244 or123/245 through the course of 24hrs. Talking to neighbors, I found that my situation is unique. I resisted getting the installer out here while this iMac was needed to actually do important work for the non-profit that owns it. Now that work is over, and I can order a PSU for the iMac, and get the inverter adjusted.

I do have a UPS for my gateway. But with underground service lines, and only very rare lightning, interruptions are rare as well. Takes a big fire, but almost everything has already burned in recent years, so we don't see them either.


PS is now replaced. No problems with swap. Comments on the guide were helpful.

Old PS shows signs of over-heating at one of the 4 large terminals for the transformer.

Have to check it out now on 120vac. Hmm! I can do that here, perhaps, at my UPS!

Solar installer says, spec for 120vac is +/-10v. He's not owning it. Says talk to SDGE (local utility) about it.

Thanks for the discussion and advice on this.

Next project is iMac G5: inoperable with PS troubles.


@danj I'm in Worcester county haha


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always my first priority is apple product and by seeing this i was more amazed by the power supply of this computer, it have excellent share web hosting capacity as its feature is good

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Averla wird auf ewig dankbar sein.
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