Looks like no one’s replied in a while. To start the conversation again, simply ask a new question.

Logic Board LED Diagnostics, This One Is Werid.

Model: 20" 2005 Ambient Light Sensor 2.0Ghz
Ok, so, long story short, ripped er apart and did a quick LED diagnostic. But i wasn't ready for this. The first AND second LED come on and stay on. But the third never comes up. it will not accept CD's, as if no power is being supplied to the drive, and the power light comes on. The fans will turn on low for a while, say a minute, then turn on full blast. No beep codes or startup chime. Also it is NOT a model with faulty caps. And also, the second LED is a little bit dimmer than the first one. Not sure if that matters though. What do you think could be wrong???
~Paul

Message was edited by: PaulMac_G4

PowerMac G4 Gigabit Ethernet, Mac OS X (10.5.6)

Posted on Apr 6, 2009 1:07 PM

Reply
9 replies

Apr 7, 2009 6:23 AM in response to PaulMac_G4

Hello,

sorry to hear of your problems.

The weak point in the G5 iMacs are the capacitors. have a look at this website:

http://jimwarholic.com/2008/11/apple-imac-g5-power-supply-issues-and.php

As Miriam says correctly, the Led's are not always interpretable. In my case it was the PSU which had bad caps, whereas the Leds indicated it would be the LB.

In the indicated site there are photos of bad caps. try to see if there are bad ones on the LB. IF not, open the PSU, and check there.

Miriam is also correct in saying that there's nothing "replaceable". This is valid for most people (me included!) -- but --:

in my case, it was the PSU. I looked with an oscilloscope on the different output voltages, and found the 3V was unstable. I put a 1 microF cap across it which made it quiet enough so that my iMac would work again.

perhaps this helps.

Please, report back

Thomas

Jul 5, 2009 7:14 PM in response to PaulMac_G4

Hi PaulMac.

Did you have any luck with the diagnosis?

I have same problem. Imac 17" G5 ALS. Chimes. LED 1& 2. No video. Fans to max after 30 secs. Can't reset PRAM or start in Safe Mode ( no keyboard input ? ) SMU reset only makes power light glow constant on front. All caps look good on Logic board and inside PSU.

Cannot see anything logical that would be causing this. Any help greatly appreciated.

Cheers, L2K8

Logic Board LED Diagnostics, This One Is Werid.

Welcome to Apple Support Community
A forum where Apple customers help each other with their products. Get started with your Apple ID.