09-20-2010, 06:23 AM

Hi,

I was using my 24" Alu iMac on Saturday when all of a sudden is went dead. Now it won't power on!

I've changed the power cable, which hasn't solved the problem and I've tried resetting the SMC.

Now, I suspect the power supply is shot, but before buying a new and replacing it how can I be sure it is actually the psu that has died and it's not something else and/or the logic board??

Any help gratefully received!

Cheers
Martin

09-20-2010, 08:21 PM

Now, I suspect the power supply is shot, but before buying a new and replacing it how can I be sure it is actually the psu that has died and it's not something else and/or the logic board??

You can't really be sure what's wrong until you get power to the machine. However, a failed logic board generally won't take out the entire power to the machine. You may wind up replacing the PS and then find out that something else caused it to fail. I have no idea how much a new PS would cost nor how difficult it is to replace one in an iMac. The iMac generally is a difficult machine to work on since the entire display has to be removed before you can gain access to the inner works.

Go to iFixit: The free repair manual and price the part and also look for instructions to change out the PS.

09-28-2010, 03:32 PM

Update: I've replaced the power supply with a new unit.

It hasn't fixed the problem. As you say if it was the logic board at least it would power on.

09-28-2010, 05:05 PM

Unfortunately, that's the risk you take trying to trouble shoot a dead iMac. Did you look around on the ifixit site? You might find some trouble shooting tips there that may lead you to the problem. And yes, my experience with bad logic boards is that they usually do not kill everything. Most of the time when a logic board goes out you'll still get power to the fans and sometimes the display.

09-29-2010, 08:25 AM

I've look on ifixit, that's where I found the guide so I could remove the power supply.

One other thing, when my iMac was working I've always found that the power on button needed to be pressed a few times for it to come on, not all the time just sometimes - or I had to hold down the button for a few seconds to make it come one.

I wonder if the actual power switch has gone kapput? Would do you think? Is it easy to replace?

Cheers
Martin

09-29-2010, 01:57 PM

LED readout:

Power cord is plugged in,turned on at wall.

From the left

1. Green light on
2. Off
3. Doesn't seem like there's an LED here anyway
4. Off

This is with the NEW power supply installed, yet it still won't turn on.

Cheers
Martin

09-29-2010, 02:24 PM

One other thing, when my iMac was working I've always found that the power on button needed to be pressed a few times for it to come on, not all the time just sometimes - or I had to hold down the button for a few seconds to make it come one.

I wonder if the actual power switch has gone kapput? Would do you think? Is it easy to replace?

Sometimes it's the simple things that elude us. I would definitely change out that power switch before moving on to additional trouble shooting. The ifixit site may have the part and will certainly have instructions. Nothing is really easy to repair on an iMac except changing out the memory, but if you were able to swap out the PS, the switch should be easier.