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

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iMac 20" A1174 dead, but +/-12VDC at PSU

Hi All !!!

Got an iMAC Model# A1174. 2006. 20" display. Last 4 of the SN are VU2S.

When you press the power button, NOTHING happens.

Disassembled the unit. What I discovered is: Power button tests good. If I DISCONNECT the multipin connector on the motherboard (logicboard?), then plug the power cord in, I hear the HDD spin up. No fans nor LEDs, just the HDD. if I re-connect the multipin connector on the motherboard, then plug the power cable in, nothing. Press the power button and again nothing.


With system normaled up but display and multipin connector removed I have the following on the PSU :

Grey wire 1 = +12VDC

Grey wire 2 = -12VDC

If I re-connect that multipin connector back into the motherboard, I get 0 VDC on those grey wires. With the multipin connector disconnected and the power cable plugged in, I can read various DC voltages (5, 3, & 12).

I have a bad feeling that the problem is possibly with the motherboard since the multipin connector has all the appropriate voltages on it before I plug it back into the motherboard.

Any ideas of how to test the PSU any further, or how to isolate this problem better?

THANKS ALL in advance!


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Any one else have any ideas?


@rms8 can you go on here and identify your iMac for us completely?


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Well, it ended up being a defective power supply after all despite having good voltages pre load. Put a load on it (plug 14pin connector back into logicboard) and it would fail.

I'd like to give a special mention to eBay seller "atlantaecomm" {} for actually sending me a power supply, inverter board and logic board to test with. Without a known good PSU, I was convinced it was a faulty logic board. So thanks to Steve

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@rms8 the very first thing you want to di is tell us what your diagnostic LED's are showing you.

The iMac (20-inch Late 2006) has three built-in diagnostic LEDs and a front power-on/sleep LED

on the main logic board that can help you to troubleshoot the computer.

To Access the Diagnostic LEDs:

1. Follow the take apart instructions to remove the RAM access door, front bezel, and lower EMI


2. Locate the SO-DIMM slot and LVDS video connector. The three diagnostic LEDs 1, 2, and 3 are

located below the battery and to the right of the memory slot. Note that the LEDs are

marked 1, 2, 3 as show below. An additional front bezel LED is located in an opening at the

center of the right speaker.

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LED #1

• Indicates that the trickle voltage from the power supply has been detected by the main

logic board. This LED will remain ON whenever the iMac is connected to a working AC power

source. The LED will remain on even when the computer has been shut down or put to sleep.

The LED will turn off only if the AC power source is disconnected or the power supply is


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.

Front LED

• Indicates that the computer has power but no video signal (e.g., the computer is starting up

or the display has entered Sleep mode, turning off the video signal). This LED will pulse when

the entire system has entered Energy Saver mode.

To check the voltafge you may want to consider checking this great guide. Slightly younger model, but should still prove valuable.

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Thanks for the quick reply oldturkey!

Unfortunately, the iMac I have does *NOT* have the diag LEDs. Nor does it have that IC just to the left of them seen in your pic.

The Front LED does nothing.

The link you provided to measure power is for a newer iMac than what I have. My multipin connector is 7x2 (14pins).




Rob, see if there is a small piece of black tape on the bottom of the logic board to the right of the RAM slots. If so remove it to uncover the LEDs.



I have attached a pic to my original post.

There you can see there are no LEDs.....



@rms8 I remember now the very first one of these did not have the LEDs. This makes diagnostics via the internet very difficult. That's why Apple added them. When you attempt boot what lights if any do you see and what sounds do you hear?


There is ZERO ACTIVITY. It behaves as if it is unplugged. I have determined it must be the logic board since :

A.) I see all voltages on the end of the 14pin connector when it is UNPLUGGED from the logicboard.

B.) The HDD spins up when the 14pin connector is UNPLUGGED from the logicboard.


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Rob sera éternellement reconnaissant.
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