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Help, iMac blows fuse


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My iMac is blowing fuses in its sleep. The one in the power lead plug. I have tried another lead and another outlet. I plugged it into a plug board guarded by a 5amp fuse, the 10amp in the plug blew, so the current would appear to be coming from the machine, not from the mains outlet. Has anyone had a similar experience or have any ideas what is happening?

 

It only happens when it is asleep, I assume when it partially wakes to carry out some task.

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Can't see how a 10 amp fuse would blow AFTER travelling through a 5 amp fuse, are you sure you have that right? sound like faulty fuse to me, or something more sinister going on.

 

Don't connect any guitars or mics to it until you get this issue sorted, just in case, as you can get shocks from both.

 

You have no ground lifts or power strips that may alter the wiring (Earth etc.) to prevent unwanted noise, right?

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Can't see how a 10 amp fuse would blow AFTER travelling through a 5 amp fuse, are you sure you have that right? sound like faulty fuse to me, or something more sinister going on.

 

Don't connect any guitars or mics to it until you get this issue sorted, just in case, as you can get shocks from both.

 

You have no ground lifts or power strips that may alter the wiring (Earth etc.) to prevent unwanted noise, right?

 

It did that because the power was coming out of the Mac, never got as far as the 5. The consensus seems to be a faulty capacitor in the PSU. It is in for a replacement PSU now.t

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Only the live feed runs through the fuse on a plug, the live goes IN to the mac, neutral is what comes back out to make the loop, and that isn't subject to a fuse in the local plug. I wouldn't rule out other electrical issues there personally, as likely as PSU fault is.

 

IF somehow a reverse current is occurring then be very careful.

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Only the live feed runs through the fuse on a plug, the live goes IN to the mac, neutral is what comes back out to make the loop, and that isn't subject to a fuse in the local plug. I wouldn't rule out other electrical issues there personally, as likely as PSU fault is.

 

IF somehow a reverse current is occurring then be very careful.

So how can you account for the manner in which the fuse blew?

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Well, could be faulty fuse so it blew early, also some fuses are designed as slow/fast blow. So the 5a could be a slow blow and able to deal with spikes better, whereas the 10a could've been fast blow and less likely to hold out with a spike. Could be an electrical wiring fault somewhere between the power board and Mac. i.e. the Boards sockets, Mac's plug and the cable.

 

How many times has it blown when sleeping? And has it been during the night, or a similar time each occurence?

 

You would 90% presume the PSU is at fault, but you would expect it to fail during startup or waking from sleep too if this was the case. If there is a fault in the PSU and it's causing a short circuit then i guess that could blow the nearest plug in the line, but in those instances you would imagine the first fuse, or even breaker would go as it would cause a spike through the live which has to come upstream.

 

It must be a pain for you as you don't want to keep trying it for fear of messing the machine up, probably may need to spend some cash to have it looked at professionally if you're 100% sure it's not the cabling.

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Ah mate, what a pain. Hope you get it sorted and not cost too much! :(

 

It is indeed. Either way I am going to need a new machine, maybe next week, or hopefully I can squeeze another year out of the iMac. I don’t have the resources to go get a new one. I was working when I got the one I have, now I’m on a very small pension.

 

I figure the way to go is to get an older Mac Pro. Mainly because I can mostly fix that myself, but there are so many different models. Any tips on what to look for would be appreciated. I will be using it for modest Logic projects, (strictly amateurs stuff, just create a few tunes) and Adobe Lightroom/photoshop stuff, (again, keen ameture photography)

 

My budget would be £400/600. I figure it’s going to be 2010 2012 Vintage. Happy to stay with El Cap, maybe Sierra.

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Yeah the Mac Pro's are fantastic, my 2008 is wobbly on it's legs and some of the RAM has died - but man, it still crunches through things somehow lol, it's been a wonderful investment but i wouldn't recommend going below the 2009 models, once you get into 2010/2012 territory prices can really rise up based on spec.

 

If you go here:-

https://browser.geekbench.com/mac-benchmarks

 

And click on the multi-core toggle it will sort all Mac's by their total CPU Benchmark/Performance. If you find your iMac on the list that will give you a rough idea of where you are now. (Guessing this one? https://browser.geekbench.com/macs/238 )

 

Then just scroll up the list through the Cheesegrater Mac Pros (2009-2012) and compare to whats available secondhand - just note the single core performance vs your current iMac though, as that will be the Achilles heel on any older machine, and you want to be in the 2500-3000 upwards range ideally.

 

You'll find a sweet spot to suit your budget, and don't dismiss the Mac Mini's either.

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Nice, thanks. The longer the iMac holds out, the more I can save for a pro. I like the look of the minis and have nothing against them. I just want to be able to fix stuff myself and, as far as I am aware, there is nothing in a pro that can’t be got to and swopped out if needs be.
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While this is true it can sometimes become expensive to swap stuff out too, particularly the 2012 machines, and due to their age they can start to develop odd faults which are hard to diagnose (i've had two with my Mac Pro, both would cause boot problems with no errors and had me in circles for days, when they decided to fix themselves lol). BUT they're generally bulletproof, and if you've never owned one you'll love the build quality, very well designed - mines ran 60-70 hours a week for years and years and it's enabled me to earn good money with it - i really love what it's enabled me to do for so long, and i'm really thankful that i invested in it at the time.

 

I'm currently moving to a windows based machine and trying hard to get a good replacement for Logic, partly due to expense on new Macs, partly due to the way Apple are moving their products have me concerned, and of course the ability to fix/upgrade elements yourself - the way things are going, i just don't know - depends what the new Mac Pro will be like and how much i can embrace using external drives for tasks other than archiving/backups.

 

Luckily there's been a Cubase 50% offer for crossgrades this month so i've got Cubase Pro for 150 quid and i'm really pleased with it, picked up a good spec Win 10 i7 tower on ebay for 230 quid and it's brilliant. I'm missing Logic though, despite Cubase impressing me and seeming that it will do me well, and i miss simple things like iMessage and how MacOS works - the feeling that you're not being spied on (lol). I really like this forum too, which is a big part of being a Logic owner i feel, it's a pleasure to visit and communicate with people here.

 

But i'm gonna persevere with it, at least until the new Mac Pro's come out, and i can assess the situation better then. I use my machines as an income, and i have 2 desktops and laptop needed to be updated. Because of the lack of decent desktop machines throughout the years i've just not made the jump already. The problem i face is a 5-6k spend on upgrading, if the Mac Pros are 4k start then maybe 6-7k. OR i go Mac Minis with external drives like many ex Mac Pro owners are doing on here.

 

We'll see how it goes, but yeah, you'll love the cheesegrater Macs, they're not quite as easily fixable as your typical PC where you can mix and match parts, but they are a damn sight better than any other Mac out there in that regard! :)

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For me it’s availability and cost of parts, if you get an issue with any main board it can get pricey and you need the correct one or the SMC will cause odd results like the fans running at full constantly. If you’re facing paying 200-250 for board on a 400 quid machine that you’re not sure will fix the issue it’s a bit of a gamble.

 

Also GPUs you have to be careful with as if they aren’t Apple certified they will not present an image at boot, which can leave you stuck if you have any startup issues.

 

But the one thing I’ve had in the past are faults that are near impossible to diagnose until you start switching parts out, and as you’re buying secondhand it leaves you unsure if the part you’ve purchased even works, this has happened to me twice with faulty parts.

 

As they age it’s not uncommon for them to decide not to boot one day, but you can normally take the power out let them sit for 10-15 mins and they’re good again.

 

Wiith pc’s you can pick up an array of different components of course, and even older machines you can buy new components for. With Apple you’re always within the ecosystem to a degree which has its pros and cons.

 

On the plus the design of the Mac Pro’s are very good, if you get the right replacement part it will literally slide in to position and just work! Like Lego :-)

 

On the earlier Mac Pro’s RAM was also a bit more fussy, in regards to matching pairs (if you had 2x modules and one failed it would fail the other too rendering machine unusable), but the second gen which you’re looking at are much better.

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  • 2 weeks later...

If it's not the PSU, and it's not the cable or plug then the only other logical place to look would be around the switch before the PSU, as there's capacitors that could arc and cause it to fry on wakeup. Just don't mess with it yourself as those caps can hold quite a charge, i got a bolt from a machine that had been turned off for a while and it wasn't nice.

 

I've repaired a fair amount of iMacs but never touched power issues outside of replacing PSU before, so don't really know a whole lot more - don't suppose the people who are looking at your machine also carry out PAT testing? It's a quick process if they have the testers, and will show up if you've got some kind of strange earthing issues going on.

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Update.

 

The machine still blows fuses, but only when coming out of stand by. It is not a fault with the power supply. The current is definitely coming out of the machine and blowing the first fuse it encounters. It does not blow when the display wakes. It functions fine apart from this. Consensus is the fault is on the logic board.

 

I am fund raising for a replacement machine and have had two strong pledges from pals already. Thanks for all the help and advice on this rather odd fault.

Francis

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  • 1 year later...
Wow this was a while ago now. I had an SSD put in the SuperDrive bay on that machine. I took it to a tech who replaced the power supply and it made no difference. So I had him yank my SSD and I continued to use it in target display mode for a bit. One day I tried the put drives to sleep setting and lo and behold it was fine. It must have been that extra drive. By this time I had replaced it anyway, so I sold it on.
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