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How to Measure iMac G5 Power Supply Voltages at Pinouts of PSU | According to Jim

According to Jim

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Measuring iMac G5 Power Supply Voltages at Connector Plug Pinouts

Exactly how how do you test the PSUs out on the Apple iMacs?
How do you turn on the iMac G5 power supply when it is out of the computer?

Apple iMac G5 PSU With Ambient Light Sensor Shown

iMac G5 Power Supply Connector – P-1

1. +3.3 – BlackA3B 12. +3.3 – BlackA3B
2. +3.3 – BlackA3B 13. +12v – BrownA3B
3. GND – BlackB4B 14. GND – BlackC4B
4. +5v Gray/PurpleA4B 15. On/Off – Gray
5. GND – BlackB4B 16. GND – BlackC4B
6. +5v Gray/PurpleA4B 17. GND – BlackC4B
7. GND – BlackB4B 18. GND – BlackC4B
8. PG – Blue 19. +12v – BrownA3B
9. +5.1Vsb – Purple 20. +5v Gray/PurpleA4B
10. +12v – BrownA3B 21. +5v Gray/PurpleA4B
11. GND 22. +20v to +24v – Brown

On the 661-3350 power supply and other similar PSUs, jumper pins 15 (gray) and 16 (blk/gnd) to turn the PSU on. With the power supply on, you should be able to read all the voltages listed above with a DC voltage meter. Between pins 22 and any GND pin, you will see approx. 24vdc, which is needed for the backlight. Note that the plug is numbered on the wired side of the connector plug. You will need some good lighting to see the numbers. A small flashlight comes in handy.

When reading the voltages, it is always a good idea to check both for proper DC voltage and AC ripple voltage. Note that AC ripple voltage should be relatively low, in the low millivolts range.

From what I have been able to tell, the other power supplies in both the 17 inch and 20 inch iMac G5 computers all used the same DC voltage pinout arrangements. I believe the voltage pinout arrangements are different on the Intel iMacs and some of the iSight models.

Please read the detailed information for repairing Apple iMac G5 power supplies.

Note: (see below) PG acronym represents the Power Good signal and VSB represents Voltage Stand By.

If anyone has more information for any of the power supplies (especially the pinout arrangement) used on the various Mac products, including the various PPC models, Intel Models, and Power Macs, please send it to me.

Thank you.



Voltage pinouts listed above cover the following Apple PSUs: 661-3350, 661-3289, 614-0353, 614-0296, 614-0297, 661-3351 614-0923 614-0352 614-0294, AP14P46, 614-0398, 614-0326, 661-3625, 661-3289, AP13PC97, 614-0279, DPS-180SB, A 614-0334, 614-0366, 614-0326, 614-0398, 614-0353, 614-0328, 661-3627, 614-0327, 614-0325, 614-0365, 614-0329, 661-3290, Manufacturer Part Numbers: DPS-180QB-1A Rev 01, API4PC47, DPS-180QB ) along with a number of different manufacturers including: (ACBel API3PC96 – Celetronix Q45B – NPFC), and additional manufacturers’ part numbers than what is listed here.

PG acronym represents the Power Good signal. I found the following reference in the Wikipedia when it comes to talking about power supplies in general for PCs.

In addition to the voltages and currents that a computer needs to operate, power supplies also provide a signal called the Power-Good signal, sometimes written as Power_OK or Power_Good or you can distinguish it by its gray color. Its purpose is to tell the computer all is well with the power supply and that the computer can continue to operate normally. If the Power-Good signal is not present at startup, the CPU is held in reset state. If a Power-Good signal goes down during operation the CPU will shutdown. The Power-Good signal prevents the computer from attempting to operate on improper voltages and damaging itself.

The ATX specification defines the Power-Good signal as a +5 volt (V) signal generated in the power supply when it has passed its internal self-tests and the outputs have stabilized. This normally takes between 0.1 and 0.5 seconds after the power supply is switched on. The signal is then sent to the motherboard, where it is received by the processor timer chip that controls the reset line to the processor.

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Category: Apple, G5, iMac, iMac G5, PSU
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  • Ken Williams says:

    I found the following on ambient light sensor: Firefox won’t let me highlight the important stuff but the 4th paragraph captures the question. I hooked the PSU back up and tried to download and mount the temp monitor App. But only get about 10 minutes to work with the iMac before it shuts down. Darn it. Can I sub a 614-0326 with a Delta 614-0327 PSU ? Only $6.95 for the unit on the web.


    What are the differences between the second generation or “Ambient Light Sensor” iMac G5 models?

    Please note that the iMac G5 “Ambient Light Sensor” series was introduced on May 3, 2005 and discontinued October 12, 2005.

    Like the original iMac G5 systems, the “chassis” of the “Ambient Light Sensor” iMac G5 models rest upon an aluminum stand with an adjustable hinge, and it supports the “Video Electronics Standards Association (VESA) mounting interface standard” which makes it easy to mount the system directly on a kiosk, wall, or articulating arm.

    Additionally, as the name implies, all “Ambient Light Sensor” models have a sensor under the edge of the display that dims the sleep indicator light when the room is dark — a nice touch for a system setup in a bedroom.

    The major differences are summarized below in this handy chart:

    iMac G5

    1.8 17″ (ALS)

    2.0 17″ (ALS)

    2.0 20″ (ALS)


    1.6 GHz

    2.0 GHz

    2.0 GHz

    System Bus:

    600 MHz

    667 MHz

    667 MHz

    Level 2 Cache:




    Memory Type:

    PC3200 DDR

    PC3200 DDR

    PC3200 DDR

    Std. RAM:

    512 MB

    512 MB

    512 MB

    Max. RAM:

    2.0 GB

    2.0 GB

    2.0 GB


    17.0″ TFT

    17.0″ TFT

    20.0″ TFT





    Video Card:

    Radeon 9600†

    Radeon 9600†

    Radeon 9600†

    Video RAM:

    128 MB

    128 MB

    128 MB

    Hard Drive:

    160 GB††

    160 GB††

    250 GB††

    Optical Drive:

    8X “Combo”

    8X DL “Super”

    8X DL “Super”

    AP Extreme:




    Bluetooth 2.0:








    Model No:




    Orig. Price:




    †These models have an ATI Radeon 9600 with 128 MB of DDR SDRAM.
    ††All hard drives are 7200 RPM.
    *AirPort Extreme (802.11g) and Bluetooth 2.0+EDR pre-installed.

    December 13, 2013 at 7:23 PM
  • Lorenzo Klunder says:

    Hi Jim,
    I have a iMac A1058 with troubles of rare graphics on video and shutdown automatic actions, searching info about this problem, I found your post about how to check the DC voltages on PSU, and AC ripple. My PSU appears to be fine, the only doubts is about on pin 9 (+5.1Vsb) with 4.99v instead of 5.1v, and pins 10, 13 and 19 (+12V) with 11.7v instead of 12v, this differences may be the cause of troubles on this iMac ???
    Thanks in advance

    January 30, 2015 at 9:40 PM
  • Jim Warholic says:

    @Lorenzo… While the voltages are close to what they should be, I would also check and verify the ripple voltage on the voltages themselves. I am not sure if you have actually measured the ripple. To do that, if you have a Digital Volt Meter, you can place the setting of the meter to AC voltage, and measure how much ripple is present on the DC voltage. For example, the AC ripple voltage on each of the DC voltage power supply levels should be in the low millivolt levels (less than .010 volts [10mV] AC). If you are getting upwards of .500 volts (500mV) AC ripple, then the capacitors could be faulty on the power supply itself.

    Note also, under load conditions, the ripple can climb exponentially. So if you were playing videos, then the power supply that is supplying the appropriate voltages for the video card could bog down (significantly dropping) the DC voltage and increase the ripple current, manifested by an AC ripple voltage on the DC voltage supply.

    Another point of understanding is that if the capacitors on the logic card or video card are bad, this can have the same affect of bad capacitors in the power supply, because it would be overloading the power supply in trying to maintain the proper voltage to whatever component areas onboard the circuit boards.

    January 30, 2015 at 10:42 PM
  • Lorenzo Klunder says:

    Thanks for your quick response; I did measures of AC ripple with my oscilloscope and in all voltages don’t have ripple, the signal is totally flat on PSU; only I detected the 12V line a bit low (11.7V without load); about the capacitors on logic board, only one it had leaked and bulging (1000uf/16v) and they was replaced but all others looks like fine on working order although I don’t know if the capacitance and ESR is correct, I only checked one of 1800uF/6.3V that is near of the 1000uf caps group and it was measured good ( about 1920uf) and ESR is good.

    The iMac works power on but show strange graphics on the video screen, is locked and turn off by itself, about a one to two minutes; I don’t sure if processor fan works, all happens very quickly .

    What is you recommendation ???? I have to change all capacitors ??.

    Thanks in advance

    January 31, 2015 at 2:24 AM
  • Jim Warholic says:

    It’s difficult to know for sure of what the problem is. Note that if one of the capacitors was bulging, it is likely that some of the other capacitors are bad even if they are not showing signs of bulging. However, given that some of the other capacitors are probably bad, there could be other things wrong besides that. Note that the PSU could be defective in other ways, which may be causing the shut down. Make sure all fans are functioning also. It could be that something is overheating and tripping out the over-temperature condition.

    January 31, 2015 at 9:10 PM
  • Nicolas says:

    In my case the PSU only turns on when power from the 12V line is pulled like connect a fan to 12V and ground and then shorten pin 15 and 16

    without the fan i measure 21 V on pin22 and 5.1V on pin 9 nothing more
    with the fan i can measure all other voltages

    removing the fan during testing results in turning off the psu as well

    February 19, 2015 at 7:16 AM

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