Connecting Ethernet cable causes shutdown

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Connecting Ethernet cable causes shutdown

Our 17" iMac suddenly shutdown and refused to start up - makes the start sound but shuts down after a few seconds.
Managed to get it going by removing all cables and resetting SMU. Then connected to network thru Airport.
The moment I reinsert the Ethernet cable the Mac shuts down. Thought it might be a faulty cable, but does the same with another cable which works fine on another Mac. Problem only happens when the cable is connected to the router, indicating it is not a short in the Ethernet port.
I suspect the Ethernet card in the iMac. Any other suggestions?
Any tests I can run to identify the issue?

iMac Core Duo, Mac OS X (10.6.3)

Posted on Apr 22, 2010 2:00 PM

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Answer 1

Dah•veed

Level 9

66,487 points

Apr 22, 2010 2:13 PM in response to Johnnz

An iMac has a SMC and the steps for resetting the SMC are different from another Mac resetting the SMU. And apple has revised the process since the iMac Core Duos were introduced.

Are these the steps that you used?
Reset the SMC
• Shut down the computer.
• Detach the computer's power cord.
• Press and hold the power button for 5 seconds.
• Release the power button.
• Reattach the computers power cable.
• Turn on the computer.

Run the Hardware Test on the original Install DVDs that shipped with your iMac.

Dah•veed

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Answer 2

Johnnz Author

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Apr 22, 2010 3:44 PM in response to Dah•veed

That was the SMC steps I was using.
But now there is a more major problem: I left the iMac on extended hardware test while I did other work on another Mac. When I came back the iMac had shutdown and now will not startup despite repeated SMC resets.
All the happens is the power-on chime, then immediate shutdown (all but power cable are disconnected).
The original install disk is still in the drive.
At least previously I could get going and use Airport. Could it be the hardware test has killed something which was in the process of falling over?

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Answer 3

den.thed

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Apr 22, 2010 4:24 PM in response to Johnnz

Is the LED light on the front off, on, flashing once or flashing SOS?

http://support.apple.com/kb/HT2674

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Answer 4

Johnnz Author

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Apr 22, 2010 4:32 PM in response to den.thed

The light comes on when the power button is pressed. No flashing. Goes out when it shuts down a few seconds later.

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Answer 5

Dah•veed

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66,487 points

Apr 22, 2010 4:34 PM in response to Johnnz

Could it be the hardware test has killed something which was in the process of falling over?

Or coincidence that it finally failed during the Hardware Test.

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Answer 6

Dah•veed

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Apr 22, 2010 4:36 PM in response to Johnnz

Maybe the power supply has failed.

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Answer 7

Johnnz Author

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Apr 22, 2010 4:46 PM in response to Dah•veed

The power supply failed and was replaced a few months ago. Do you think there may be a connection with the current problem?

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Answer 8

den.thed

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Apr 22, 2010 4:52 PM in response to Dah•veed

That way also my thought!

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Answer 9

Dah•veed

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Apr 22, 2010 5:02 PM in response to Johnnz

Are the symptoms similar or the same? Did you get a guarantee?

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Answer 10

Johnnz Author

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Apr 22, 2010 5:04 PM in response to den.thed

It's back to Apple then. Maybe we got a dud PSU as a replacement. . .
Puzzling tho, why it started OK using Airport but as soon as an Ethernet cable was plugged in, it shut down. Also misbehaved if shut down then a cable was plugged in.
Maybe Ethernet ports are early in the startup check cycle and if PSU is on the way out, that kills it.

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Answer 11

den.thed

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Apr 22, 2010 5:14 PM in response to Johnnz

Yes, it's definitely hardware related and needs to be throughly tested!

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Answer 12

Johnnz Author

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Apr 22, 2010 5:11 PM in response to Johnnz

No the symptoms now are different and seemed (at least initially) to be related to Ethernet. The PSU just died before - came into the room and Mac was no longer running, no response to power button.
This time we get a chime and LED light (for a second or so).
Before the hardware test it was starting and operating OK, using an Airport connection to the network but died whenever an Ethernet cable was plugged in.
Also before the test, resetting the SMC got it going again. Now it is just a chime and LED - then nothing.
PSU was replaced by an Apple Authorised Service Centre. I guess I'm about to find out if such repairs have a warranty (and if in fact, the problem is related to that).

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