[Veltliner]

Today it happened the second time:

I put my 24" 2.16 Ghz white iMac to sleep, and the little light is pulsating nicely.

In the morning, the light is out, and my Mac is dead.

It doesn't start, nothing.

I unplug all cables, and after one minute I plug them in again.

I press the power button, I hear it click inside, the white light goes on - and out again. No start-up. If I press the power button again, nothing happens.

I unplug again, up to fifteen minutes, and the same thing happens again.

At the eight or ninth attempt, finally, start-up.

Is this software or hardware related?

Other things that go wrong with sleep: my iMac doesn't go to sleep by itself. You have to use the power button to do that.

Also: when the screen shuts off, it sometimes comes on again with no reason. (No idea if this has any connection, I'm just listing all the symptoms connected to "sleep").

My fear it's the mother board. But why does it finally start up at the eight attempt? (Took much more attempts today than the first time this happened).

[msuper69]

Well, since no software can be running until you power up the Mac, it's not a software problem.

Your hardware is bad. Contact a repair service.

[Snow-i]

Not just yet. I'd try resetting the SMC and PRAM first, see if that helps at all.

[seanc]

Not a new round of power supply failures I hope...

[CharlesS]

It certainly sounds like the power supply to me.

[Veltliner]

There's another detail:

When you shut off a Mac he remembers what Windows were open.

In iTunes, the software opens at the play list you last had open. I found that when I managed to start the computer today (iTunes had been in the background when I set the computer to sleep) iTunes opened at a playlist that I had open two days ago.

[Veltliner]

Originally Posted by Snow-i 

Not just yet. I'd try resetting the SMC and PRAM first, see if that helps at all.

I'll try this one.

I understand that the power supply is quite an expensive part.

[reader50]

Originally Posted by Veltliner 

In iTunes, the software opens at the play list you last had open. I found that when I managed to start the computer today (iTunes had been in the background when I set the computer to sleep) iTunes opened at a playlist that I had open two days ago.

This just means the computer crashed. iTunes may save state when it quits normally, or the HFS+ journal log was rolled back a little bit. So iTunes opened to the state it was in the last time the prefs file was saved.

[AKcrab]

Originally Posted by Veltliner 

I understand that the power supply is quite an expensive part.

You should HOPE it's just the power supply and not the logic board. The power supply isn't that expensive, should be in the neighborhood of $150. (plus labor)

[P]

Power supply seems likely if it died while in standby (S3). Most of the motherboard is turned off in that state - basically only the RAM and the memory controller is running, and they are not running hard. I think Apple's PSUs have a low-power mode for when the machine is in standby (to improve AC conversion efficiency - the PSU in my homebuilt HTPC does that, for instance), and if one of the caps involved in that mode is shot, you could see the behaviour you mention. OTOH, I've seen something very similar on a PC that turned out to be a motherboard issue, so you never know.

Replacement PSU for that model runs $140 at ifixit, and closer to $100 at unidentified Google merchants, while the motherboard is close to $1000 according to Google. I would not pay $1000 - a new iMac is a much better deal at that point.

[Veltliner]

I talked to my favorite Apple Tech and he says it sounds like a software problem.

He says the computer is caught in a memory loop, and after a while unplugged this memory is cleared, and this is why it started up.

I will use DiscWarrior and see what bad files he'll find and if it will occur again after that.

[Veltliner]

If it was the power supply, wouldn't it die at other instants as well, not only after a long sleep?

If it is the memory loop problem - it could connect to the problem that my Mac doesn't go to sleep at all by itself, and that the monitor, switching off through energy saver, sudden flashes to life without any reason.

[Veltliner]

Originally Posted by reader50 

This just means the computer crashed. iTunes may save state when it quits normally, or the HFS+ journal log was rolled back a little bit. So iTunes opened to the state it was in the last time the prefs file was saved.

The interesting thing is that it opened to the playlist I had open two days ago. But I had at least three playlists on in-between. So it could have reverted to the second-last playlist.

[Veltliner]

Just performed a DiskWarrior 4.2 session.

Critical values in the Volume Information were incorrect and were repaired.

[P]

Originally Posted by Veltliner 

I talked to my favorite Apple Tech and he says it sounds like a software problem.

He says the computer is caught in a memory loop, and after a while unplugged this memory is cleared, and this is why it started up.

I don't buy it, and in any case it would be enough to pull the plug for 20 seconds to clear anything like that. While in standby, the computer doesn't execute anything, so how could it crash?

Originally Posted by Veltliner 

Just performed a DiskWarrior 4.2 session.

Critical values in the Volume Information were incorrect and were repaired.

That seems a likely result of the computer shutting down unexpectedly, but not the cause of it.

[seanc]

It could work like this:

Your 5VSB rail is faulty.
When you put the machine to sleep, the RAM/whatever is running off the 5VSB rail - after a while this drops out, for whatever reason.
The first time you unplug, the 5VSB rail doesn't discharge fully or maybe it doesn't even power back up when you plug the iMac in. The second time, you leave it a little longer, the caps discharge and it works OK until the next time you sleep it.

[Veltliner]

What's the 5VBS rail? Something connected to the power supply?

[seanc]

Yep.

It's part of the power supply that gives 5 volts all the time (Stand By), even when you shut the machine down.
Without it, no parts of the motherboard will be active to notice that you've pressed the on switch.

[Veltliner]

So it's nothing that is a threat to the overall computer then. The sleep cycle hardware is out. Well, that's kill number 2 after the headphone jack. As long as it doesn't influence overall computer performance I'm fine.

[Waragainstsleep]

Actually I'd bet on the LCD panel or rather the inverter board on it. These old 24s suffer a common fault. I have one now which will only boot with the inverter disconnected from the logic board. Tried another panel and it was fine.

Sadly they cost way more than the power supplies. Take the front off and disconnect the inverter next time it crashes, see if that lets it boot. PM me if you need an inverter, I might be able to help you out.

[P]

Originally Posted by seanc 

It could work like this:

Your 5VSB rail is faulty.
When you put the machine to sleep, the RAM/whatever is running off the 5VSB rail - after a while this drops out, for whatever reason.
The first time you unplug, the 5VSB rail doesn't discharge fully or maybe it doesn't even power back up when you plug the iMac in. The second time, you leave it a little longer, the caps discharge and it works OK until the next time you sleep it.

Does the RAM run off the 5VSB in S3, though? I thought the 5VSB was only for when the machine was in soft power off (S5). I'm not saying you're wrong, I don't know the ACPI specification off the top of my head, but the rAM usually runs off the 12V rail (downconverted to whatever that particular RAM needs).

[seanc]

Originally Posted by P 

Does the RAM run off the 5VSB in S3, though? I thought the 5VSB was only for when the machine was in soft power off (S5). I'm not saying you're wrong, I don't know the ACPI specification off the top of my head, but the rAM usually runs off the 12V rail (downconverted to whatever that particular RAM needs).

I have no idea, I was wildly hypothesising with something that could co-incide with sleep & power up. I have a particular PSU which will power up and work OK, turn it off and back on, the 5VSB doesn't come up, or short protection kicks in. Not investigated it further other than changing all of the capacitors.
RAM usually runs at 1.8v, so I'm not sure why it would be running off of the 12v rail, in fact, it probably runs off of 3.3v.

Chuck in the fact that Apple's power supplies don't particularly stick to any specifications (24v anyone?) and you've got yourself a recipe for fun.

[Veltliner]

I now turn my Mac off every night, just in case.

From a turned-off state no problem powering on.

It's probably my best bet to not give an overnight sleep another try. Keep it running the way it runs well...

[P]

Originally Posted by seanc 

I have no idea, I was wildly hypothesising with something that could co-incide with sleep & power up. I have a particular PSU which will power up and work OK, turn it off and back on, the 5VSB doesn't come up, or short protection kicks in. Not investigated it further other than changing all of the capacitors.
RAM usually runs at 1.8v, so I'm not sure why it would be running off of the 12v rail, in fact, it probably runs off of 3.3v.

For some reason, it's easier to convert DC from a high voltage. I know that the processor (which runs at roughly 1V these days, depending on the model) and the GPU (same) both run off the 12V rail for instance. I suspect that RAM does the same. I'll see if I can confirm that.

Anyway, your theory is as good as any. I just wanted to see if you knew something clever about the ACPI states that I didn't, because these problems show up all too often.

[seanc]

No clever knowledge over here, maybe I'll do some research.
As for CPUs running from the 12V rail, you're correct.

[Waragainstsleep]

DC converted from AC is kind of an approximation. You take an AC signal and smooth it out using capacitors. There is a threshold input voltage where it becomes easier to produce your required output voltage.

[Veltliner]

The problem expands now to start-up from shut-down.

I shut down my Mac yesterday night.

When I pressed the power button this morning, the light went on, the start-up chord sounded - and was interrupted in mid-sound as the start-up attempt was interrupted and failed.

After unplugging, same game, light on, mechanical sound inside, magical eye light out, (no starting chord).

Even after 40 minutes of unplugged, the same game.

One thing:

If you plug it in, you hear a wheeze from (standing behind the computer) the right upper corner (the left upper corner from the front, but you can't hear it from the front)

It sounds like a fan or so. After a failed start-up attempt, this sound goes away. And is on again when you plug the computer in again.

Then I left it plugged in for a while, and it started up again.

[seanc]

Sounds like power supply to me.
Waragainstsleep may be onto something with the LCD inverter though.

[Veltliner]

The break-off of the first start-up attempt was right before the screen would light up.

The start-up problem probably occurs when the computer has been shut off for a long time or has been sleeping for a long time (overnight).

I just started it up without a problem 2 1/2 hours after I shut it down.

[P]

Originally Posted by Veltliner 

If you plug it in, you hear a wheeze from (standing behind the computer) the right upper corner (the left upper corner from the front, but you can't hear it from the front)

It sounds like a fan or so. After a failed start-up attempt, this sound goes away. And is on again when you plug the computer in again.

Then I left it plugged in for a while, and it started up again.

Teardown pics of your Mac seem to rarer than rocking horse poo, as a friend of mine likes to say, but from what I can see there's nothing in that corner except for a fan. A fan not quite spinning up can be an indication of the voltage not being high enough, but usually fans have a pretty large margin for those sort of things. If that's what's happening, wither your PSU is dying or something else is disturbing the voltage on that rail. Something like a broken inverter...

I think that only thing you can do now is to follow the advice of Waragainstsleep and try booting with the LCD disconnected to see what happens. The fact that it comes back to life after a while is a strong indicator of PSU failure in my mind, but some googling shows that that inverter is indeed a known problem. I can't seem to find anyone who sells that inverter board without the panel, which obviously drives up the price.

[seanc]

Not even iFixit.
I can only think of a fan causing a wheeze as well, especially if it powers up then down.

[Veltliner]

This morning the computer started up with no trouble. Wouldn't a faulty PSU be always faulty, not on and off?

What really puzzles me is that my computer doesn't go to sleep by itself. I let it stand for three hours, and when I came back it was still not asleep.

Couldn't there be a problem with the OS that is related to start-up/sleep?

I have snow Leopard, but only the upgrade disc (Could you use this disc to reinstall the OS?)


PS: I had a bad inverter, and screen and inverter board were exchanged under warranty. The bad inverter caused a serious hum, that increased when you dimmed the screen brightness, and disappeared with full blast. There is no hum now, even when I reduce the screen brightness.

[AKcrab]

A faulty PSU could be hit and miss, but eventually it won't work at all.

The logic board ultimately is in charge of power flow and sleep, so you could be looking at a failure there.

If you want to rule out OS, you'll need to boot from an external something, obviously. You should be able to use the upgrade disk to reinstall.

[Waragainstsleep]

I have sourced these inverters but I'm currently having an issue trying to pay for them.

[Veltliner]

Logic board would be bad...

I guess I'll simply reinstall the OS and see if my machine can go to sleep by itself then.

[P]

Originally Posted by Veltliner 

This morning the computer started up with no trouble. Wouldn't a faulty PSU be always faulty, not on and off?

No, it could be temperature dependent. If you have a bad cap, it could be shorting at some temperatures but be fine at others.

Originally Posted by Veltliner 

What really puzzles me is that my computer doesn't go to sleep by itself. I let it stand for three hours, and when I came back it was still not asleep.

Couldn't there be a problem with the OS that is related to start-up/sleep?

Not startup - at the stage you mention, the OS isn't even loaded yet. Sleep could be one of millions of reasons.

Originally Posted by Veltliner 

I have snow Leopard, but only the upgrade disc (Could you use this disc to reinstall the OS?)

Yes.

Originally Posted by Veltliner 

PS: I had a bad inverter, and screen and inverter board were exchanged under warranty. The bad inverter caused a serious hum, that increased when you dimmed the screen brightness, and disappeared with full blast. There is no hum now, even when I reduce the screen brightness.

Good. It seems unlikely that the replacement inverter was bad - if we do that here, forcing the customer to replace a part twice, it's called Repeat Repair and is considered Very Bad. I suspect Apple's views on the subject are similar.

At this point I'd be inclined to take a chance with a new PSU.

[Waragainstsleep]

Apple also hates repeat repairs. But if Apple hated them as much as they claim, then they wouldn't send out parts which have the exact same defect as the originals in the hope they will outlast the warranty cover this time round....

[Veltliner]

Originally Posted by P 

No, it could be temperature dependent. If you have a bad cap, it could be shorting at some temperatures but be fine at others.



Not startup - at the stage you mention, the OS isn't even loaded yet. Sleep could be one of millions of reasons.



Yes.



Good. It seems unlikely that the replacement inverter was bad - if we do that here, forcing the customer to replace a part twice, it's called Repeat Repair and is considered Very Bad. I suspect Apple's views on the subject are similar.

At this point I'd be inclined to take a chance with a new PSU.

I already contacted my favorite repair tech.

My notice of the buzzing sound that came up when I plugged in the computer, and which went away after a failed start-up, convinced him it's the PSU.

One thing bothers me: I just had my computer on for three hours without using it - it didn't go to sleep. I hope there's nothing wrong with the logic board as well.

[Waragainstsleep]

Did you ever try disconnecting the inverter cable?

[Veltliner]

Originally Posted by Waragainstsleep 

Did you ever try disconnecting the inverter cable?

No, I didn't.

The start-up failure hasn't occurred for five days now. I'll see how long it'll work without a repair. When I do the repair, I'll also - as the computer is already opened up - exchange the hard drive with a 1 Tb drive.

And, by the way, that little sound that I heard and which reminded me a bit of the inverter board hum, it's for now gone.

[Veltliner]

Just got my Mac back - 9 day wait...

Power supply unit is new now, and as the computer was already open, I put in a 1 Tb drive (Hitachi).