Model A1174 with 2 GHz Core Duo or Model A1207 with 2.16 or 2.33 GHz Core 2 Duo

271 Questions View all

iMac - no power, number 1 diagnostic LED on

Hello all

I am trying to diagnose the issue with my iMac. The only sign of life is the number 1 LED on the logic board.

This light does not come on if either the invertor or AC Line Filter are disconnected from the power supply. My iPhone does not charge if connected.

I got another power supply from ebay and am getting the same symptoms with this one.

Is there anything else I can try to diagnose the issue?

Many thanks

Dan

Answered! View the answer I have this problem too

Is this a good question?

Score 2
Add a comment
Deck the Halls
With tools and Fix Kits

5 Answers

Chosen Solution

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.

LED 3 indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

Was this answer helpful?

Score 4
Add a comment

f your iMac G5 won't turn on—the display has no picture or color, and you don't hear fan or hard drive activity sounds—follow these steps to troubleshoot the issue.

Products Affected

iMac G5 (20-Inch), iMac G5 (17-Inch), iMac G5 ALS (17-Inch), iMac G5 ALS (20-Inch)

This article does not apply to iMac G5 (iSight) computers.

Make sure that the power outlet you are plugging your computer into is working. Plug a different device (such as a working lamp) into the socket to make sure it has power, or plug your iMac G5 into another outlet.

Check the power cord. Use a power cord that you know works.

Check both ends of the power cord to make sure that the plug is securely inserted into both the AC outlet and back of the computer.

Disconnect the keyboard, mouse, and other peripherals (such as speakers) from your computer.

Remove the back cover to access the diagnostic LEDs on the main logic board (see Chapter 4 of your iMac G5 User Manual for instructions on removing the back cover).

With the back cover removed, locate diagnostic LEDs 1 through 4 on the main logic board, shown above the large white arrow in the image below.

Plug the power cord into your iMac G5 and into a working electrical outlet. Check to see if LED 1 is on or off.

If LED 1 is on, the power supply is getting power from the electrical outlet. Go to step 8.

If LED 1 is off, the computer's power supply should be replaced. Please schedule a service appointment with either an Apple Retail Store or an Apple Authorized Service Provider.

Turn the computer on using the internal power button (press the small, metal button under the fan cover as shown below).

Does the computer start up normally after pressing the internal power button?

If yes:

Press and hold the power button until the computer turns off.

Unplug the the power cord from the iMac and replace the back cover.

Return the computer to the upright position.

Plug the power cord back into the computer and press the power button on the back cover to turn it on.

Make sure the computer starts up properly. If the computer won't start up when you press the power button on the back cover but did when you pressed the internal power button, go to step 11.

If no: Reset the System Management Unit (SMU) by pressing the SMU button (the small, metal button next to the internal power button, shown below).

Note: If you're using an iMac G5 (Ambient Light Sensor) computer, your SMU was already reset when you unplugged and replugged the computer. You won't see an SMU reset button to press, and that's OK, as this action has already been done. (If you aren't sure which iMac G5 model you have, click here for help.)

After resetting the SMU, press the internal power button again. Does the computer start up normally now?

Yes:

Press and hold the power button until the computer turns off.

Unplug the the power cord from the iMac and replace the back cover.

Return the computer to the upright position.

Plug the power cord back into the computer and press the power button on the back cover to turn it on.

Make sure the computer starts up properly. If the computer won't start up when you press the power button on the back cover but did when you pressed the internal power button, go to step 11.

No: Go to step 12.

Unplug the computer and remove the back cover. Plug the power cord back in. Press the internal power button (shown below) to start up the computer. If the computer starts up now, but not when you push the button on the back cover, please contact your local Apple Retail Store or Apple Authorized Service Provider for service.

Press the internal power button (shown below) to start up the computer.

Does LED 2 come on momentarily, or not at all?

Momentarily: The logic board has detected power, but the power supply cannot maintain it. Your power supply needs to be replaced. If you have an iMac G5 (Ambient Light Sensor) computer, contact your local Apple Retail Store or Apple Authorized Service Provider for service.

Not at all: Your logic board needs to be replaced. Please contact your local Apple Retail Store or Apple Authorized Service Provider for service.

Was this answer helpful?

Score 2
Add a comment

I'm jealous, I can't get the first LED to light on my 17". from what I have learned so far the I mac runs on three voltages - 5v, 3.3v and 12v for the inverters. If any of these are shorted out (go to ground) then the iMac shuts the power off. So you probably have a bad inverter or bad bulbs not a power supply problem.

Was this answer helpful?

Score 0

Comments:

The official response to no light on the #1 LED is to replace the power supply. I was able to check my power supply with a multimeter and it tested OK so I pulled some pins and I got the #1 led to light up when I had the two 12v pins out... apparently they are for more than just the inverters as I can't get it to turn on. I had to replace the logic board because I can't trace anything on those boards and to make a long story short it now works perfectly. Just adding my 2cents, it's not always the power supply when the #1 LED is off. One last thing, a good way to test a suspect power supply is to plug it into a GFCI, if there is any leak(to ground) then it will trip.

by

Add a comment

check the RAM is seated - Mac will flash if no memory

Was this answer helpful?

Score 0
Add a comment

dear all ,

I have a lot of frustrations regarding my I mac 21,5" mid 2011 , firstly have randomly computer switch off by self than after and present situation is that computer have only funs running and black screen, at logic board there is only led number one during funs running and thats it, no other less activity ,

please any advice what to replace

Many thanks in advance ,

Igor

Was this answer helpful?

Score 0
Add a comment

Add your answer

Dan Tutty will be eternally grateful.
View Statistics:

Past 24 Hours: 4

Past 7 Days: 25

Past 30 Days: 126

All Time: 19,635