Odd fuse blowing. iMac 2010

[DAGGILARR]

Hi. I run a 2010 iMac i7 27". About six months ago I had the original 2tb HDD drive removed, and replaced it with a 1tb HDD and put a 1tb SSD in the optical bay. It has all worked fine with no issues. yesterday evening when I returned to the keyboard and hit the space bar, (my normal method of waking it) nothing, the machine would not boot. i changed the fuse in the power lead plug and that was the problem. This morning , the same thing has happened, another fuse has blown! replaced it, boots fine. the first fuse was 10amp, the new ones are 13. I don't have any 10s. Has anyone any ideas what may be causing this?

[DAGGILARR]

As a precaution I have used an alternate power lead with a 10 amp fuse, I have plugged that into an extension lead protected by a 5amp fuse and that, in turn, to a different outlet, albeit on the same circuit.

[BigRedX]

On a device with a detachable power lead, the fuse in the plug is there to protect the lead itself and not the actual device. The fuse used should be rated for the lead.

[DAGGILARR]

On a device with a detachable power lead, the fuse in the plug is there to protect the lead itself and not the actual device. The fuse used should be rated for the lead.

Hmm , Interesting. so what protects the device?

What I don't understand is why that fuse has blown twice. when there are three other things plugged into that extension lead, and nothing else has blown.

[DAGGILARR]

Another fuse just blew. it was the 10amp not the 5 in the plug board

[ef37a]

On a device with a detachable power lead, the fuse in the plug is there to protect the lead itself and not the actual device. The fuse used should be rated for the lead.

Quite. A computer that draws less than 400W max should not take out a 10 amp mains fuse even allowing for inrush current. I would hazard a mains spike coinciding with switch on but I would still expect an internal mains fuse to blow instead or at least as well as.

The mac now seems to be working ok? That just leaves the very rare event of a faulty fuse as the culprit. I would suggest not buying fuses from the corner shop but get branded ones from an electrical retailer, though I have to confess, in a long and undistinguished career in retail electronics servicing I have never come across dodgy fuses! Self igniting 13A plugs yes but not fuses.

Dave.

[BigRedX]

On a device with a detachable power lead, the fuse in the plug is there to protect the lead itself and not the actual device. The fuse used should be rated for the lead.

Hmm , Interesting. so what protects the device?

What I don't understand is why that fuse has blown twice. when there are three other things plugged into that extension lead, and nothing else has blown.

There should also be a fuse inside the device itself, normally located by the mains input socket.

I would suspect a dodgy mains lead. Do you have another one you can try?

[ef37a]

I am just wondering if the iMac has VDR surge limiters PRE internal fuse?

Maybe invest in a UPS? I suspect they are better protected from mains spikes than computer supplies. Not that we get any trouble with our mains supply really. Don't waste your money on "surge protected" diss strips.

Dave.

[DAGGILARR]

So far it has blown , in this order 1 10amp, and 2 13amp, amp another 10 amp. I have used an alternate lead.

It only seems to happen when it is asleep. I return to it and hey presto blown fuse. The last thing I did was put in the 10 amp and plugged the lead into an extension protected by a 5amp. The 10 blew. So whatever It is, is happening on the computer side, not the power outlet side. At this point I have 5amp fuses in and I have switched off all sleep modes. It still runs fine.

I am thinking that I must have a dodgy power supply in the iMac. That it surges when waking to index or time machine or something.

[Hugh Robjohns]

I am thinking that I must have a dodgy power supply in the iMac. That it surges when waking to index or time machine or something.

That would be my guess too... When 10 and 13A fuses in mains plugs and plug boards start blowing something is seriously wrong somewhere... It takes both extremely high and sustained currents to blow those fuses normally -- although some will blow purely through old age and/or repeated surge stresses.

H

[DAGGILARR]

The machine ran fine for several hours with a 5amp fuse, I had a document that had to be finished. I have now shut it down. So it does seem that it only does this when waking itself from sleep. Is there any possibility that an SMC reset would help? I am fearful about any further experimentation as to do so would involve seeing if it did it again, and as has been pointed out, it takes a belt to blow a fuse, which has to be risky for the machine, allthough it does appear to work fine if it is set to never sleep. Can I risk using it in this mode?

If it needs a new power supply I wonder how much this will cost and if it is worth it for such an old, albeit very capable, machine.

[zenguitar]

I think it's time to talk to Apple and see if they are aware of any known causes or solutions. Difficult to identify the real cause online so any advice would be uncertain.

Andy

[DAGGILARR]

I think it's time to talk to Apple and see if they are aware of any known causes or solutions. Difficult to identify the real cause online so any advice would be uncertain.

Andy

They couldn’t help, offered to recommend a certified Apple repair centre. I have someone I can take it to, so until I do it’s shut down. I just did a backup this morning.

[zenguitar]

That all sounds eminently sensible. It's frustrating, but I think you're doing the right thing.

Andy

[ef37a]

That all sounds eminently sensible. It's frustrating, but I think you're doing the right thing.

Andy

Indeed^.
Don't know macs but is the PSU integrated with the main PCB? That is how VCRs went and they were buggers to fix.
Philips were the only good guys that I remember in that the PSU was in a slim, tinplate can. The trouble was they did not go the last half inch and supply as a service replacement but sent you a "blow up kit" a bag of components and mods that took a good two hours to change!

Dave.

[DAGGILARR]

It is replaceable, but not easily.

[Folderol]

My guess (apart from a most likely faulty PSU) would be one of the EMI filter caps arcing over. They might be either before or after the the power switch.

[ef37a]

My guess (apart from a most likely faulty PSU) would be one of the EMI filter caps arcing over. They might be either before or after the the power switch.

Aha! Could be Will. The X or Y rated caps are "self healing" so they can short but then be fine afterwards. Of course, even in sleep mode there is still close to the peak 340V on them.

Dave.

[DAGGILARR]

My guess (apart from a most likely faulty PSU) would be one of the EMI filter caps arcing over. They might be either before or after the the power switch.

Aha! Could be Will. The X or Y rated caps are "self healing" so they can short but then be fine afterwards. Of course, even in sleep mode there is still close to the peak 340V on them.

Dave.

Would fixing that require replacing the power supply?

[ef37a]

My guess (apart from a most likely faulty PSU) would be one of the EMI filter caps arcing over. They might be either before or after the the power switch.

Aha! Could be Will. The X or Y rated caps are "self healing" so they can short but then be fine afterwards. Of course, even in sleep mode there is still close to the peak 340V on them.

Dave.

Would fixing that require replacing the power supply?

I would not think so. Have to get it out and have the correct capacitor fitted and have a good look for other damage and, because it is a mains side repair it will need a PAT cert.

Dave.

[DAGGILARR]

I would not think so. Have to get it out and have the correct capacitor fitted and have a good look for other damage and, because it is a mains side repair it will need a PAT cert.

Dave.

I am going to take the machine to a tech tomorrow. What should I tell him to check? If I can avoid having to buy a PSU that would be great.

[ef37a]

I would not think so. Have to get it out and have the correct capacitor fitted and have a good look for other damage and, because it is a mains side repair it will need a PAT cert.

Dave.

I am going to take the machine to a tech tomorrow. What should I tell him to check? If I can avoid having to buy a PSU that would be great.

Oooo! Techs rarely like to be "told" things! Puts zeros on bills. I would send him a link to this thread first!

Dave.

[DAGGILARR]

It turns out it is not the power supply. A new one has been tried and the thing still blows fuses when it comes out of sleep. What in the world could it be that can fire in excess of 13 amps out through the power lead and not completely fry the machine?

[Folderol]

Sorry to hear this.
Unfortunately the 'power supply' is only half of the actual supply control and distribution. At this stage I think your only option is to take the machine to a real expert.

[DAGGILARR]

Sorry to hear this.
Unfortunately the 'power supply' is only half of the actual supply control and distribution. At this stage I think your only option is to take the machine to a real expert.

I am up against the law of diminishing returns here, but yeah, that’s the thing to do. Or just use it without sleeping it.