power failure, and then recovery after rest?

[Doug Lassiter]

OK, here's a weird one. I was playing with my iMac (10.6.8) and put it to sleep manually. Then I tried to wake it and it wouldn't wake. Huh? So I pressed the power button on the back to restart it. Nothing. Pressed it again. Nothing. Aargh. Probably the power supply or the logic board. So I take it in, and show the repair folks. Yep, won't start up. Nothing at all. No screen, no chime, no fan or disk clicks. Nothing.

A few days later, they get a chance to look at it in the lab, and it boots right up. No problem. Checked the memory and SMART status on the disk. No problem.

Whaaaa?

We had a lighting storm a few days before, and the power flickered, but that doesn't happen infrequently. It is not on a UPS or even on a surge protector (my bad). I am told that the power supply can "self protect" by going into a mode that it doesn't come out of for many hours. Is that true? Of course, there was nothing to protect it from when it stopped working.

Anyone heard of this kind of thing before? I've been using Macs for decades, and have several, but I've never run into this before.

 

[lclev]

I have no idea on an imac but I have seen it on pc's. I had to replace a power supply on my pc at work so I put in a 1200 watt (yes, I need it.) If the power goes out it will not come back on until at least 5 minutes have passed and then you unplug it and toggle the on/off switch on the power supply. Scarred me when it first happened but when I read the manual that came with it, I discovered that was a feature of the power supply to protect it. I finally put it on a UPS which took care of the problem. Power outages are frequent in my rural area.

The breaking of the power connection by plugging it may have reset the power supply.

Lisa

 

[Doug Lassiter]

Hmm. Well, the iMac was replugged in when I first took it to the shop, and it didn't work then. So if plugging it in did some kind of reset, it needed to get plugged in twice to make the reset happen.

 

[harryb2448]

What has happened after the surge is an SMC reset so all is well.

 

[pigoo3]

I'm with you Harry. SMC-Like Reset is what I was thinking.

- Nick

 

[Doug Lassiter]

That still doesn't make a lot of sense, because it took an hour for me to get the machine to the shop where, when plugged in again, it still didn't work. So the power cord had been unplugged a lot more than the fifteen seconds required for SMC reset before it was plugged back in and it still didn't work. The SMC would have been reset in this way.

So let's suppose it was an SMC reset problem. Why did it decide to start up several days later, and what should I have done to fix it more quickly? Since it didn't power up, I couldn't even reset the PRAM.

 

[pigoo3]

The computer's working…be happy!

- Nick

 

[Doug Lassiter]

Yeah, I'm happy, because when I brought it in, I was told that I was looking at a $300 fix (power supply replacement) or $600 fix (logic board replacement).

But that cost me five days of backlog at the shop, at minimal cost. So what I'm wondering (beyond being happy) is why it happened, and what I'm going to do when it happens again. I'd rather not have it rest for five days in order to recover.

 

[pigoo3]

What exact model iMac is this?

- Nick

 

[Doug Lassiter]

iMac 21.5 inch, late 2009

 

[pigoo3]

iMac 21.5 inch, late 2009

Thanks for the info. The reason why I asked was…this is an approx. 6 year-old computer. Having a glitch like this happen once in 6 years is pretty rare. Thus the chances of it happening again are probably equally as rare. I agree with what you stated in the first post. I also would have thought that the logic board or power supply got fried after this power failure…and the computer would't start up. But then (as you stated) it did eventually start up)…which is great.

It sounds like the repair folks you took it to didn't have an explanation…and I'm afraid I can't think of anything either. Part of my conclusion is based on the fact that I don't know (exactly) what happened to this computer between the power failure & when you got the computer back (5 days). If I had this computer in my possession…I may have been able to do something differently that might have gotten it to start up (in a much shorter time).

And remember (according to the posts). This whole process didn't really take 5 days. Since it sounds like it sat idle at the repair place for a few days…until they had a chance to look at it. So the actual turn-around time could have been much less.

Again I say…be happy that the computer is working. If the power supply or logic board had been fried…you could very well now be shopping for a new $1500 computer (possibly a VERY undesirable situation).

If I was given the following two possible situations to be in:

1. Shopping for a new $1500 computer.
2. Have a working 2009 iMac (and "dodged a bullet" with the power failure)…but not know exactly what caused the issue.

I would certainly choose situation #2! What you experienced with this iMac may never happen again.

- Nick

 

[Doug Lassiter]

That makes sense. Yes, it certainly didn't need to rest five days. It might have been ready to restart after a few hours.

I hung out with the repair guy for an hour while he was doing system tests. Disk fine. Memory fine, etc. I am just really puzzled, from an electronics standpoint, what could have happened. He speculated that the power supplies sometimes have safe-modes. When a problem is detected, they just shut down for a while. He's seen that happen a couple of times. I have no idea what kind of problem it might have been seeing.

But no, because it happened once in six years means it is unlikely to happen for another six years doesn't really compute. If something is degrading, the fault could start happening a lot more frequently.

Yes, I agree about your two solutions. A new iMac would not really be that much more powerful than the one I have now. We're in the era when new computers aren't really a lot more powerful. They get lighter in weight, or thinner, or the resolution gets better (e.g. Retina) if you pay for it. Might have a bigger hard disk and more memory. But this machine is still, five years later, damned nice. I would have paid $600 for a new logic board.

 

[lclev]

So now to be proactive. Put the iMac on a UPC - they are really not that expensive for what they provide. And make backups using Time Machine and either Carbon Copy Cloner or SuperDuper.

Glad it all worked out!

Lisa

 

[pigoo3]

I hung out with the repair guy for an hour while he was doing system tests. Disk fine. Memory fine, etc.

Was the iMac powered on or off during these tests?

But no, because it happened once in six years means it is unlikely to happen for another six years doesn't really compute. If something is degrading, the fault could start happening a lot more frequently.

I wasn't thinking or talking degrading at all. But if something is degrading…then that's a totally different situation. A power outage problem and degrading hardware are different issues. The discussion in this thread was related to a power outage.

- Nick

 

[Doug Lassiter]

Was the iMac powered on or off during these tests?
I wasn't thinking or talking degrading at all. But if something is degrading…then that's a totally different situation. A power outage problem and degrading hardware are different issues. The discussion in this thread was related to a power outage.

- Nick

Not sure how you'd test anything if the machine was powered off. The test being done was with Apple's very extensive system test software with the system powered on. That system test resides on an external drive that you boot to. I had not seen that before. Pretty slick.

The power outage that was being discussed here was that the iMac could not be powered on. If something is degrading in the logic board or the power supply, that could happen. There was no ac power outage within days of this failure, so no strong evidence to associate that power failure with the problem at hand.

As to a UPS, yes, I probably ought to get one, but the next thing I get will really just be a surge suppressing plugstrip. I use SuperDuper routinely, and do scheduled backups every night.

 

[pigoo3]

Not sure how you'd test anything if the machine was powered off.

I was just asking Doug! Maybe the sequence of events seem very clear to you. But when you mentioned the detail about the testing…you didn't mention at what point in this whole scenario that the testing took place. So things were getting confusing.

If I don't ask questions for clarity…then I can't get a good idea of what's going on…and then I can't help to the fullest.

Have a good one Doug.

- Nick