LED #4 RED is on after 2 minutes after start a machine.

Computer shutting off after LED 4 on red. Could not possible

to run ASD. CPU heat sink close to cpu very hot but upper

heat sink park cold.

Any ideas ?

Thanks

⟐ Commented November 20, 2016 at 15:12 MST

⟐ Commented May 24, 2019 at 3:53 MST

Please help

⟐ Answer accepted December 08, 2017 at 11:06 MST

Six months ago had a OS crash on Tiger. No original install disks so I removed the original 250GB HDD and installed a new WD 640GB HDD successfully.

Now I installed Leopard on this drive. Shortly after this I stated to have KP and freezes.

Then I would have to restart the iMac 2 or 3 times to get it to boot - make the "bong" sound to start up.

At the time I thought it was the on button of the back of the iMac.

This past Saturday I was making a fresh copy of my new drive using TM and an external FW drive and the iMac froze or had a KP.

Went to reboot and no luck. iMac turns on but will not start up with the normal chime or bong. Eventually the fans go into high speed.

God lots of advice from Macresource forums and I decided to replace my PRAM battery.

All went well but it did not help. Same problem.

I did notice two capacitors on the MB with brown spots on the tops. Guess it could be the problem.

I have read reports on what the led lights mean as many people confuse this model with previous models and they are totally different.

Currently my led lights read... led1 comes on and stays on when the iMac is plugged in. led2 comes on when I power up the computer.

I did pull off the power supply and did not see any damage.

I am ready to change out the capacitors on the MB if anyone can confirm that is the problem.

Tahing in advance for any help or support.

I am going to start reading up on this topic some more so I can gear up my mind to take on this repair.

I have a soldering gun but don't know the watts right off hand.

I am new to this site and can not even find where this post is located at. I have to login to my profie to find it.

Almost got scammed today by someone offering me their iMac on crigslist.

So need to come back to reality and fix my own iMac!!!

Thanks

Matthew

⟐ Answer accepted March 19, 2014 at 3:46 MST

Than I installed the OS X Leopard and connected with the time machine to restore the backup files.

This took multiple hours and this morning I got the message restore complete please reboot. which I did but now after rebooting the gray screen turns to a dark gray screen and the message in a black box appears "Restart computer by holding down the button..." Unfortunately everytime I do this I end up with the same screen.

I run disk utilities and repair disk, but can't detect any problems.

⟐ Commented March 11, 2026 at 12:57 MST

⟐ Answer accepted March 04, 2014 at 9:24 MST

⟐ Edited August 31, 2010 at 14:38 MST

⟐ Answer accepted February 01, 2010 at 20:38 MST

The pinout of the 14-wire connector is:

Group 1:

INV_CPU_HI

SYS_POWERUP_L_BUF

PP12V_ALL

PP12V_ALL

PP5V_ALL

PS_GND

PP3V3_ALL

Group2:

LCD_PWM

POWER_GOOD

PS_GND

PP12V_RUN

PS_GND

PP5V_RUN

PP3V3_RUN

I presume the LCD_PWM is used to adjust the brightness of the LCD back light, but what are the "INV_CPU_HI" and "SYS_POWERUP_L_BUF" pins for?

any help will be greatly appreciated! :)

⟐ Answer accepted April 27, 2018 at 7:26 MST

⟐ Commented February 21, 2016 at 0:20 MST

⟐ Answer accepted May 22, 2014 at 3:51 MST

Thanks.

Larry

⟐ Answered April 23, 2019 at 18:38 MST

Wish to replace 1 gb ddr2 sdram with 2 gb

⟐ Commented September 27, 2018 at 11:16 MST

I am going to start working on my dead iMac G5 with isight, but with all the mentions in these threads of the diagnostic LED functions. I've yet to find a link or list of what they mean.

After a brief power outage, my old iMac probably was fried in the surge when power came back, so I suspect all I need to know is the one for a dead power supply. But still.

This is a follow up question to the information you kindly provided above: The 1st LED stays lit when I plug it in, but when I push the power button, LED 2 flickers on for less than a second and then goes off again. The iMac stays black.

I have tried to reset the SMU by plugging it in while holding the power button, but nothing has changed.

The computer became bricked after a brief power outage (and was the only machine in the house not on a power strip).

Any ideas?

⟐ Commented October 30, 2016 at 3:50 MST

iMac G5 20" Model A1145 Microphone Replacement

⟐ Answered January 07, 2010 at 11:59 MST

Bluetooth continues to work so I can connect a keyboard & mouse with bluetooth.

⟐ Commented March 31, 2020 at 11:42 MST

⟐ Answer accepted January 11, 2016 at 5:25 MST

Can one of the temperature sensors (harddrive or other) be causing this false overheating failure?

If so, where are the temperature sensors that enable this light to go on?

⟐ Answer edited November 03, 2014 at 15:34 MST

⟐ Answer accepted November 10, 2013 at 4:41 MST

another iMac, cant recognize as well.

I did PMU reset, re-checked all cables- okay

Any ideas?

⟐ Answer accepted March 06, 2013 at 5:12 MST