Logic board or power supply?

Ok. I've read all the posts about the Power Supply and the LED tests etc. My problems have been unique and intermittent

About a month ago, my iMac was in SLEEP mode. I went to wake it up with a keystroke or mouse move (not sure which) and it simply turned off. No shutdown, the light and power went “out.” Dead.

I went to power it up and it had no response. Annoyed and upset, I went to sleep and left it all night. The next AM – being new to the iMac diagnostic world – I found instructions on and executed a reset. It took a few tries but it came back. I put the incident behind me.

Then a few days later, it happened again. Same sequence – system dies on sleep “wake up.” This time I was more in tune with the procedures. So I did the reset of the Power unit (again – unplug from wall, wait 15 seconds, plug in, wait 5 and power up.) On these tries I had weird results:

  • First' (try) – nothing;
  • Second – white light and drive motor sounds for about 2 seconds, then stops dead;
  • Third – white light and drive motor sounds for about 4 seconds then dead;
  • Fourth – it boots and sits on grey screen. (NOTE: this was the only time it sat on grey screen. ) After this last try I put the System disk in and she booted up.
  • Concluding actions after booting - I ran diagnostics on the hardware – all GOOD; I ran Diagnostics on the drive – all good not repairs needed.

Yesterday she was dead again (same sequence.) On FixIt and MacSupport I’ve read many of the posts. I opened her up. Got familiar with the insides. Tested it open and she booted back up ok. NOTE: I could not find the LEDS on this unit while it was dead and open. But when she came back to life when the cover was off, I could see the LED under the tape. Thus – I can assume – when the system was “dead” we had NO LED ACTIVITY AT ALL. And when she was working yesterday I did a few cycles of Power off through the OS and turning back on. During this sequence when when it was off – we had 1 LED working. But…….. (finally and I am almost done.)

She died again yesterday evening. And NO LED at all when plugged in.

Conclusion as of this 12-13–2011

I ordered a new Power Supply. Seems as the time of failure is increasing, the PS is having issues. Hope to install tomorrow or Thursday.

Does anyone think its something other than the Power Supply? Can this be a logic board issue? (I hope not.) ''italic text''

Can we assume that the “startup” issues I noted above where it would start for 2 seconds then stop are related to needing sufficient boot up voltage? This is where I am going but any input would be appreciated. And I will update the posting as I get the new PS installed.

Update

UPDATE:

The Imac failed a few days ago. I installed the NEW Power Supply today. I got the green light and its booted up fine. I will monitor it for the next 2 weeks and update my post. I agree it most likely is solely a power supply failure and nothing more. But will update the post should the same symptoms come back. Happy Holidays.

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Deck the Halls
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Your assumptions are in order. A trickle charge is sent from the power supply to the first LED. If the first LED is not lit the power supply is not working. I would suspect a possible bad connection except a trickle charge doesn't carry much current or voltage. - Just enough to supply the LED.

The diagnostic LEDs to the right of the RAM slots (this may be covered by a piece of black electrical tape). - you noticed that.

LED Startup Sequence

LED #1 = Power available.

If no LED is visible:

• Verify AC source

• Verify known-good AC cable is connected

• Verify cable connection between AC inlet and power supply

• Verify cable connection between power supply and logic board

• Verify power supply

LED #1 + LED #2 = Power available, and system is powered on.

If second LED is not visible when power button is pressed:

• Verify power button connection to logic board

• Verify power button functionality

• Verify cable connection between power supply and logic board

• Verify power supply

• Verify logic board

LED #1 + LED #2 + LED #3 = Power available, system is powered on, and video card found.

If third LED is not visible after power on:

• Verify that MXM video card is seated properly

• Verify logic board

If no lights are coming on you need to replace your power supply. A trickle charge is sent from the power supply to the first LED. If the first LED is not lit the power supply is not working.

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Hello,

As my problem is quiet the same, I don't know if I have to open a new topic?

For sometime, I had more and more difficulties to switch on my iMac when it was cold (after a night or more, I had to reboot it up to 30 time to really wake it up!), and a lot of sudden "sleep mode" with anything to do but reboot it…

Few days ago, finally refuse to boot:

no gray screen, no sound, just the light on in the right corner… and a new weird sound when it tries to boot!

After trying everything I could (reset PMU, PRAM, change the ram etc etc), I decided to open it.

I cleaned it of all the dust accumulated in 2 years (when I changed the original HD) and checked everything I could, but I didn't notice anything suspect.

The 1st LED is lit when the cable is connected,and when I push the power button, the 2 and 3 are lighting up too (and stay lit), and that's all.

The fans are on, everything else seems to light on, but there is still the same unusual noise and the display stay black and the HD don't seem to start up.

Only the white light (on the right beneath the display) stay lit.

I strongly suspect the power supply, but before buying a new one, I'd like to know what you think of it : )

If some has a clue or an advice, it would be great!

And sorry for my english… I'm a f… French ;-)

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Thierry, previously converted to its own question. Check on here difficulties to switch on my iMac when it was cold

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Hi FAlbano! Hi Everyone!

FAlbano I'm curious to know about your iMac. Did it work fine after changing the power supply?

Or did you find out what the problem really was?

I have a 2013 iMac 27" and it has started randomly going off. No warning it just goes black.

And refuses to turn back on for some time. Moreover, how long it stays on seems to depend on how long I've left it off

If I try to start it again after say 10 minutes, it turns on but shuts off again in a minute or even during startup.

If I leave it for a few hours then it might work for half hour or so the next time.

When I left it alone for more than 24 hours it worked for more than an hour before it shut off.

I'm quite puzzled and it's become impossible to work on this machine.

Thought I'd like to have some clues before I take it to the service people. Don't want them to dupe me into unnecessary part replacements.

All advice is much appreciated. Thank you all!

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Hi,

Try to look if your model is covered by this replacement program:

https://www.apple.com/support/imac-hardd...

If not, you can try to start your iMac in "safe mode" (shift key down):

if it doesn't go black anymore, it's probably a Graphic Card issue…

You can make the iMac to work again, (without Graphic acceleration):

you have to find the GC extensions and removed it from the Extentions folder (keep it safe somewhere to put it back when the issue is fixed).

This way, you can use your iMac nearly the same as usual even if the display is slow.

If your iMac is not yet considered "vintage" by Apple, you can ask for a quote to replace it.

If it's not possible, there is a way to fix it yourself with a 2009 model, but if yours is a "slim" one, it might not be easy to open it…

On my 2009 iMac, I removed the GC, "toasted" it in an oven and it's been working flawlessly for 1 year now !

You can find every details here:

https://discussions.apple.com/thread/495...

Good luck : )

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FAlbano will be eternally grateful.
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