Become a MacRumors Supporter for $25/year with no ads, private forums, and more!
  • Did you order new AirTags? We've opened a dedicated AirTags forum.

reebzor

macrumors 6502a
Original poster
Jul 18, 2008
869
1
Philadelphia, PA
Hey so a friend gave me an iMac G5 to work on. It won't turn on. I left it plugged in for a couple hours and nothing happens. I've read a few things and tried them: Reset SMC, Manually reset SMU, pressed the Internal power button, etc. The only thing that happens is LED 1 is lit when the machine is plugged in. I have checked all of the capacitors and they all look perfect, no bulging or leaking. Is there anything else I can try?
 

Shotgun OS

macrumors 6502a
Dec 18, 2006
505
4
Ohio
I have a similar problem with my iMac G5 iSight; however, it will making a noise as if it is revving up and is on, but the screen never comes on.
 
Comment

zen.state

macrumors 68020
Mar 13, 2005
2,181
5
Certainly sounds like a power issue. Lucky for you the iMac G5 is one of the easiest Macs to open and work on.
 
Comment

burnout8488

macrumors 6502a
May 8, 2011
540
10
Endwell, NY
Try replacing the PRAM Battery. (CR2032 button cell)

I've read that these power supplies require the 3V from this in order to allow the computer to power on. My iMac's battery had 2.8v, wouldn't turn on. Replaced it with a new battery that metered @ 3.2v, fired right up.
 
Comment

reebzor

macrumors 6502a
Original poster
Jul 18, 2008
869
1
Philadelphia, PA
So I installed a new PRAM battery, still nothing. Like I said, LED1 is lit when AC power is connected which means that the PSU is supplying power to the board. There is no visible damage to the board or anything. I don't have access to another iMac power supply to test this with... Looking for something else... anyone?
 
Comment

666sheep

macrumors 68040
Dec 7, 2009
3,629
238
Poland
Man, see this link I've posted in my first answer. Especially what LED 2 means. You need a new (working) PSU. One (or more) rails in your PSU doesn't deliver right voltage to logic board. That's what I've tried to tell you earlier. ;)
You could remove PSU and check it for bad caps, if you'll see them bulged, leaked etc it will be more than obvious where the problem is.
 
Last edited:
Comment

reebzor

macrumors 6502a
Original poster
Jul 18, 2008
869
1
Philadelphia, PA
Man, see this link I've posted in my first answer. Especially what LED 2 means. You need a new (working) PSU. One (or more) rails in your PSU doesn't deliver right voltage to logic board. That's what I've tried to tell you earlier. ;)
You could remove PSU and check it for bad caps, if you'll see them bulged, leaked etc it will be more than obvious where the problem is.

You didn't explain anything you just posted a link to an article that I already read.

Apple said:
Above this arrow, you'll see four LEDs:

LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.
LED 2 indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

Like I said, I had already read that article and referring to the bold text: My LED1 is on, which according to that means my PSU is working correctly. Since my computer is not turned on, LED2 shouldn't be on. That is how I interpreted the information.

I'm not saying you are wrong, in fact I believe you are correct. The Apple article you linked to is not worded very well. I found a different article that explains the LED's better and it led me to believe the power supply is definitely the issue. Now it's time to open it up and check it out.
 
Comment

666sheep

macrumors 68040
Dec 7, 2009
3,629
238
Poland
You didn't explain anything you just posted a link to an article that I already read.

Yeah, maybe I used a kind of mental shortcut ;)

I meant that if LED 2 doesn't come on after pushing power button PSU is always the first suspect.
Keep us posted :)
 
Comment
Register on MacRumors! This sidebar will go away, and you'll see fewer ads.