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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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  • Jim Warholic says:

    Hi Kim,

    The powering down and powering up problem is typical of the the bad capacitor problem. I always say, you’ve got to fix what you find bad. In this case, having bulging caps on the MOB can in fact cause the problem you describe. I would definitely fix the MOB with new caps to begin with. Then, if you still have a problem, the original bad capacitors on the MOB could have caused something to go out in the PSU other than the PSU caps themselves.

    Refer to my other Apple articles for more information.



    February 8, 2012 at 2:40 PM
  • Kim Damsgaard says:

    Hi Jim

    Thanks for the fast response and help:-)



    February 9, 2012 at 1:14 AM
  • Peter says:

    Jim, I am testing the PSU from an iMac g5 20″ and only getting voltage from pin #9 at 5.2 v and #22 at 20.8 v while #15 and 16 are jumpered together. So that means my PSU is going to need some repair right, I saw, on visual inspection, only one cap with a slight bulge on top. Is my assumption correct as I am not getting any voltage or really about .27 volts out of the other pins that I will need to repair this PSU?
    thanks for all your info on the website, so helpful really appreciate it.

    February 22, 2012 at 11:10 AM
  • Jim Warholic says:

    Yes, you are correct with the fact the PSU is missing those other voltages. I would first start with the capacitors. It is also possible that something else may be blown on that particular power supply.

    February 22, 2012 at 11:27 AM
  • Guy says:

    I have a 20″ Ambient Light Power supply that does not work. I have not checked voltages, but visual inspection shows no bulging caps. I am trying to figure out if I should replace the power supply or try the caps first. I have seen many of these bulgig caps over the years so I know what to look for and none of these caps look bad. what do you suggest?

    February 27, 2012 at 8:58 PM
  • Jim Warholic says:

    Hi Guy,

    I would say that you probably need to check those voltages first. Also, if the first LED does not light on the logic card with the PSU plugged in to the AC, but not turned on, then that is showing that something else is probably wrong with the PSU other than the capacitors.



    February 27, 2012 at 10:03 PM
  • Guy says:


    I can’t figure it out but all of the voltages are like you said above. Could one of these things start working again after being discharged all the way? I am going to put it in the computer and see what happens. I have one of these and my parents also have one. Theirs stopped working so I took mine out and traded with them. Weird that it seems to be working.

    Also on your pinouts #8 PG-Blue is 5 Volts. Another thing to note is that you can’t use the case for the ground on your meter. I used a paper clip to jumper 15 & 16 so I used an alligator clip to clip on to the paper clip for ground.

    I was also told by a Dell tech to look for the X pattern on top of the capacitors, these were the bad ones. We had hundreds of GX270 motherboards go bad because of these bad capacitors. The replacement motherboards had capacitors with a K stamped into the top of the capacitors. This might help folks to figure out which ones an likely to be bad.


    February 28, 2012 at 7:12 PM
  • Jim Warholic says:

    Hi Guy,

    It could be that when the PSU is placed under load, that is when the problem shows itself. It could be that something else is bad on the PSU.

    Thanks for the input about the Dell motherboards. Dell was not the only one to have problems. I just heard a report that Samsung TVs had a similar issue with bad capacitors too.



    February 28, 2012 at 8:20 PM
  • Kev says:

    Could you please explain what A3B, A4B, C4B etc do mean?

    March 1, 2012 at 3:37 PM
  • Jim Warholic says:

    Hi Kev,

    That is what someone supplied to me for labeling. It may be where the wires go on the circuit board as a reference point. However, don’t worry about those specific references, just the wire numbers when measuring the voltages.


    March 1, 2012 at 6:58 PM
  • Steve says:


    Would you happen to know the pinout voltage for the backlight inverter? For a imac G5, 1.6ghz. (6 pinout)

    March 18, 2012 at 11:25 AM
  • Jim Warholic says:

    Hi Steve,

    Sorry, no information in that area. Maybe someone else that reads the comments knows the pinout voltages for the inverter or can point us in the right direction.



    March 18, 2012 at 12:03 PM
  • Joe says:

    How can I confirm that my iMac 17″ G5 PSU (P/N 614-0293) is working properly? I have removed it from the unit but I want to make sure it’s working before I proceed to repairing the logic board. When this PSU is out of the unit, do I also jump pins 15 and 16 in order to turn it on so that I can test the voltage values? Any help would be appreciated.

    April 20, 2012 at 10:37 PM
  • Jim Warholic says:

    Note that the voltage pinouts should be the same between the 17 and 20 inch iMacs. Follow the procedure above for testing.

    April 21, 2012 at 9:20 AM
  • steve kim says:

    I have an imac G5 and it turns off on its own. After its turn on and if you dont do anything, (like moving the mouse or opening an application) the power may stay on for 15 minutes before the power goes out. Any help will be much appreciated.
    Steve Kim

    June 15, 2012 at 1:20 AM
  • Jim Warholic says:

    To Steve,

    I suspect either the PSU or the MOB capacitors are problematic. Refer to my other Apple articles. Also, I would double check the temperature of the machine with one of the free temperature monitor programs. Just Google Search free temperature monitor for Mac.



    June 15, 2012 at 7:43 AM
  • Stan_ says:

    Dear Jim
    I want to replace the power supply in the 20 “iMac G5 ALS on the power supply of 17″
    Is such a change?

    September 26, 2012 at 8:06 AM
  • Jim Warholic says:

    I’m not sure of all the differences between the PSUs. I would be more inclined to think you could install the PSU from a 20 inch iMac and install that in the 17 inch iMac but not the other way around, due to the 20 inch one requiring more current to drive the video circuits. Just my thoughts. I don’t have any hard data on this though.

    September 26, 2012 at 11:34 AM
  • Dubau says:

    French owner of an iMac 17″ Intel with power supply out ! Is that power supply the same as in an older iMac 17 PPC ?

    November 5, 2012 at 11:05 PM
  • Jim Warholic says:

    The Intel iMacs have different power supplies compared to the PPC versions.

    November 6, 2012 at 2:12 PM
  • Ricky says:

    Hi, I have a IMac 17″. Im really not sure if its the power supply thats busted. I opened it up and plugged in the power supply and a single green light lit up. I tried pressing on the PCU and the reset button, but still to no avail. It still doesn’t turn on it just have that single green light at the mother board. Could you assist me on what you think the problem is?

    The power supply looks exactly the same as the picture above.

    November 12, 2012 at 3:47 AM
  • Jim Warholic says:

    The first thing I would do is open up the PSU itself to see if any of the capacitors are bulging.
    Then, I would try powering it up with the PSU out of the computer and measure the voltages. Remember, to turn it on requires jumpering two pins. Jumper pins 15 (gray) and 16 (blk/gnd) to turn the PSU on.

    November 12, 2012 at 7:51 AM
  • Kenny Swope says:

    I have been researching the tar out of the internet and am looking for a pinout of the iSight iMac 17″ 1144 model DC-DC connector that cables into the logic board. I already know that the PSU and the DC-DC are bad. I have replaced the caps on the logic board and want to test the MOBO out with an ATX PSU that I have on the bench so I don’t spend a lot more trying to see if this is worth saving.

    Has anyone seen a pinout of the 12 wire connector at the DC-DC converter for the 1144 iSight iMac? Everything I have found have been of the earlier models.

    November 17, 2012 at 9:28 AM
  • Chris says:

    Hi Jim,

    I found your site searching for a pinout of the power supply in the iMac G5 20″ iSight model. The power supply looks like the one you call type S. Do have any information on what the voltages should be on that output connector? I am measuring 12V to from grey to black which is likely but 180mV from brown to black which doesn’t seem likely. For what its worth, none of the caps on the PSU are blown or bulging and there isn’t the slightest odor of fried electronics.

    I sure hope you can help me out, there’s a wealth of info out there on the regular G5 iMacs but not the iSight ones for some reason.

    Thank you kindly,

    December 16, 2012 at 11:41 PM
  • Jim Warholic says:

    Maybe someone has the wiring diagram for this. If anyone does, feel free to email it to me.


    December 17, 2012 at 6:54 AM
  • Giuseppe says:

    Hello Jim, I have an iMac G5 17″ ALS, the computer starts without a problem and it works fine with leopard, but the CPU temperature is 58/60 degrees in idle and 85/88 in load. If I try a system reboot from OSX, I have a shutdown after the bong sound with brutal power loss. For restart the machine, the only way is to reset the SMU. l don’t have any problem If I shutdown the iMac from OSX before, and then I restart it from power switch button after. I look the capitors caps on the logic board and that’s it in good visible condition. It’s a PSU defect for you?

    July 22, 2013 at 3:29 PM
  • Jim Warholic says:

    To Gluseppe,

    I would open up the power supply and take a look at those caps. By the way, even if the caps don’t look bad on the logic board or the PSU, it is still possible the caps are faulty.

    July 25, 2013 at 11:50 AM
  • Christopher S says:

    Hi, Thanks for this informative page.

    I have a bad 614-0293 power supply for an iMac G5. Is it ok to replace it with a 614-0294?

    I have been trying to find what the difference is but have not been able to find anything that talks about this. Your help would be much appreciated.

    August 1, 2013 at 8:00 AM
  • Jim Warholic says:

    I have on occasion used one PSU in place of another. I do not know what the exact differences are, other than maybe the internal layout and design. However, I think there are some differences between the PSUs for the 17 inch model and that of the 20 inch model. I think the PSU used in the 20 inch model had higher current capacities (though I am not sure of that). I don’t think there was anything published that talked about the specific differences.

    I do know there is a slight difference on the PSUs for those that have the ambient light sensor attached and those that do not.

    August 1, 2013 at 6:03 PM
  • paul vail says:

    Hello Jim and everyone else,

    Working on a G5 iSight 20″. The compact power supply type (pn 614-0378). Also seeking nominal voltages for the five lead connector (brown and twin grey leads. The largest cap (150uf / 420v) is bulging – no others. Symptoms present as no power or noise when pushing the power button. PRAM battery ok. Will run out and get a replacement large cap and see where that takes me. Any other links or clues on how to walk the board to determine where there may be failure are most welcome. Happy to post/send pictures and results.


    August 24, 2013 at 10:48 AM
  • Ken Williams says:

    So Jim,
    Like several others I have a iMac G5 produced 06/2005 that I bought off Craig’s list here in Seattle. Bare bones so loaded my old hard drive files and software using Newertechnology USB Drive adapter. The unit has been working great for about a week and half but now shows the symptoms of a poor performing PSU. The iMac will start up but never completes booting. All three LEDs check out on the logic board, the fans run fine. So I pulled and tested the PSU with your charted voltages. All pins provided the correct voltage. So decided to be smart and used the PSU from my 2004 iMac which does not have the ambient light sensor and only the number 1 LED lights up. Won’t power up when the power button is pushed. unfortunately, I broke the male connector to the ambient light sensor. Do I need this? If so, do you carry the parts? Still in the dark on why the iMac is shutting down. All capacitors look fine externally.

    December 13, 2013 at 2:27 PM
  • Jim Warholic says:

    You might check the temperatures using one of the free temperature monitor programs. Sometimes the PSU under load is the issue. I would also open up and physically look at the capacitors inside the power supply. Also check the capacitors on the main logic board. Even slightly bulging caps are an indication that the caps are bad. Additionally, the caps can be bad without any bulging. They tend to dry up with heat and age, and lose the ability to filter the ripple current. So, the caps on the PSU and the caps on the logic card work in tandem. If one or the other, or both are not functioning properly, heat will be generated, and the PSU will shut down.

    As far as the connector for the sensor, no I don’t have that available (look online at some of the Apple parts places). I don’t recall if that is absolutely necessary for the iMac to operate. I am not sure what the symptoms would be without it functioning. Maybe the display would be bright all the time, or dim, but I am not sure.

    December 13, 2013 at 4:21 PM

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