Measuring iMac G5 Power Supply Voltages at Connector Plug Pinouts
Exactly how how do you test the PSUs out of the iMacs?
How do you turn on the iMac G5 power supply when it is out of the computer?
iMac G5 Power Supply connectors – 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, jumper pins 15 (gray) and 16 (blk/gnd). This turns the supply on and you should see all the voltages listed above with a DC voltage meter. Between pins 22 and any GND, 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.
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.
If anyone has more information for any of the power supplies used on the various Mac products, including the various PPC models, Intel Models, and Power Macs, please send it to me.
Thank you.
Regards,
March 27th, 2010 at 11:06 AM
Hi Jim, I have a first generation G5 that fell in to the Apple extension program and they fixed it some time ago I believe by replacing the mother board. 2-3 years on and I have been having video problems and now the unit is dead, well not quite dead as the first two test LED’s come on but not the 3rd nor do the fans work, the disk does power up but no video. I have been following your excellent article and have now replaced all the caps on the mother board but unfortunately that didn’t fix it. I have read on the net that if the 2nd led is on then the power supply is OK. So before I have a go at replacing caps on the PS have you any tips regarding the the symptoms. Incidentally when I tested the Caps I removed from the MB they all tested ok and all within there tolerances. Thanks again for your well documented articles on the G5 I will now have a go and test the voltages from the Power supply. One more thing, do you ship the Cap kits to UK? I have had great difficulty in sourcing the correct sizes etc.
Cheers
Mike
March 27th, 2010 at 4:22 PM
One of the aspects about a power supply being arbitrarily labeled good with just indicator LEDs coming on is that folks can be easily fooled into a type of go no go indicator.
First off, there are numerous voltages that could be partially faulty, through excessive AC ripple, because of bad caps, that can directly affect various areas of the iMac, and still allow it to somewhat boot up.
I would personally do a physical inspection of all the caps inside the power supply itself, and also do a very close inspection of the logic board capacitors. Look for any bad caps with even a slight amount of bulging. Sometimes it is very subtle on the bad caps themselves. There might only be a slight bulging top on a bad cap. Additionally, folks are starting to find that many of the bad caps are not even showing physical signs of being bad. Some folks have replaced the caps on the MOB and low and behold, their iMac now works. If you have tried everything else, then this really is about the only option left prior to just giving it away, or selling it on Craigslist or eBay for iMac G5 parts.
As far as measuring the caps are concerned; once the caps are removed from the MOB, it is somewhat of a static test even if you are using a capacitance or ESR meter. The reason is that the bad caps can severely break down under heat and loaded conditions, and might check somewhat OK in a static mode, out of the circuit, with no voltage or ripple current applied. By the way, because a power supply can be putting out more ripple current under load, this can directly affect capacitors throughout the computer. For example, a defective power supply can weaken the caps on the logic card, and bad capacitors on the logic card can weaken the power supply. It is the law of the weak link in the chain that breaks first. That is why, it is important to verify both the PSU and the MOB have good capacitors.
I suggest you take a look at some of the other articles I have written in regards to the iMacs for more detailed information. Follow my Apple link for the details.
As far as the measurements on these voltages with the PSU out of the box are concerned, they are not under loaded conditions. A flaky power supply can act up under load and produce a lot more ripple, and reduce the voltage below the operation threshold. I have been looking for a power supply tester for an iMac; one that will measure the voltages under loaded conditions, but as yet have not found one. There are numerous PC PSU testers to be found, but none for the Macs that I know of. If anyone knows of one, let me know.
Yes, I do ship to the UK and numerous international locations. Visit my ecommerce website at www.jwestsales.com. J West Sales for the Apple inside you, for more information on international shipping.
June 29th, 2010 at 10:37 AM
Hi Jim, I replaced the caps I got from you. The Comp worked for about an hour then shut off and would not go on. I then came here and checked the pins and I only have voltage on the 24 line and the 5 volt line on pin 5. What should I check next? Diodes, rectifiers etc. I have an SMD re work station so this type of work is not too hard for me. I did use the heat gun to get some of the caps out as it was easier to do that way. Wonder if that hurt anything?
Athansios
June 29th, 2010 at 2:57 PM
Hello Athansios,
It is possible that something else is blown out in the power supply. I know that there are a number of surface mount devices on the bottom of the power supply board, and it probably is a bad idea to use a heat gun to get the caps out. Note that I think you can do a better job with direct heat from the tip of a soldering iron, than you can do with the heat gun. The solder melts relatively easy with a soldering iron on the PSU. It’s a different story on the MOB. So, yes, it is possible something else is hurt by the use of it. At this point in time, it might be time for a new PSU.
Write to be directly if you want to know where I recommend buying a new power supply.
Regards,
Jim
July 6th, 2010 at 5:28 PM
Jim,
First of all, thank you for all the info on the bad caps. My PSU went out Sept. ’09 and I was soon up and running with a new PSU that I installed. Lately my Imac G5 has been turning off, erratically at first, now within a minute of it booting up. There is a click or pop and it is dead. I pulled the new PSU and checked the pin outs and they all had the correct voltage. I left it powered up for a couple hours, the case was only warm, and the voltages were still ok. I reinstalled the PSU and the problem is still there. Is there anything else I can check, or is the next step changing the caps on the motherboard and seeing if that works?
Regards,
Geoff
July 6th, 2010 at 8:03 PM
Hello Geoff,
Many times the PSU is only the tip of the heat shut down problem. Sometimes the motherboard caps are bad, even though there might not be any visual signs of failure. Here is a recent article I published titled Fat Caps and Ripple Current. The article is an email conversation I had with an expert electronics designer about underrated capacitors and the excessive ripple current that results from poor electronics engineering designs in a wide array of consumer and commercial electronics equipment.
Unfortunately, you might be in a situation where the parts failure cascading effect has resulted in the relatively new power supply, now being pushed to the limit because of weak capacitors on the MOB, and thus you may have a “new” bad power supply too. The popping sound is probably coming from the PSU.
I believe that many folks have experienced the Apple iMac G5 merry-go-round failure effect over the years with having their iMacs repaired by Apple. I have heard numerous stories (actually many have written directly to me) over the years, about how Apple Genius Bar folks have first replaced the motherboard, then months later the power supply was replaced, then again months later the motherboard again. This story has been repeated over and over, and one has to wonder, what’s wrong with the design? Is it bad caps, or is it a bad design, or is it Apple squeezing the maximum amount of dollars from each unit they sell by having the designer save a penny here and a penny there, just long enough to get it past the warranty period? The article Fat Caps and Ripple Current addresses some of these issues and is worth reading.
As far as where you currently are at with your iMac G5, you might want to read some of the other articles about the iMac computers.
Below are a listing of the articles for Apple iMac G5 repairs and capacitor replacements:
*Apple iMac G5 Logic Card (Mother Board) Repair and Capacitor Locations
*Apple iMac G5 Power Supply Repairs
*iSight Logic Board Capacitor Locations
*Disassembly Procedure for iMac G5 First and Second Generation iMacs
*Measuring the DC Voltages on the iMac G5 Power Supply Pinouts: (You are here)
*Comparisons of the Different PSU Types Used in iMac G5 Computers
*Hard Drive Replacements
*Hard Disk Drive USB Adapter For Mac and PC
*Add a Second Monitor to Your iMac G5 Computer – Extend the Desktop
*Soldering Tips for Lead-Free Soldering
*Installing Capacitors on MOB and PSU Tips and Helps
I hope that helps everyone out a bit.
Regards,
Jim
July 7th, 2010 at 9:14 AM
Jim,
Thanks for the reply. I had already started reading the other articles on repairing the motherboard. It is good to have a concise listing of all the articles so I don’t miss one. “Fat Caps and Ripple Current” is definitely worth reading to understand what is going on. I am glad you pointed out the cascading effect because I was just looking it at as the PSU or the MOB and not the effect of one on the other, and that is key. I’ll read it all twice before I get started.
My rant is about “Just in time manufacturing” since I constantly see signs of “Junk in time” and the cascade effect of bad components being shipped and turning millions of finished products into junk.
Regards,
Geoff
July 15th, 2010 at 2:53 AM
Hi Jim,
Are you sure that the pin 15-16 power supply activation test is safe and proper to run on all 661-3350 power supplies? The last unit I tried to activate (supposedly new) began making a sizzling sound when I hooked it up. The power supply I tried before that, had just had a capacitor replacement and did the exact same thing.
July 15th, 2010 at 9:25 AM
I have had many folks confirm this before I posted it.
Yes, I am sure that pin 15 and 16 are proper to turn on the power supply. I tested it in the past, but just to make sure, I decided to repair one on the bench that I have as a spare dead iMac G5 for trouble shooting purposes just now. When I first opened the iMac, I found 7 blown caps on the MOB and then opened up the PSU and found 6 additional bulging caps in there too. I tried jumpering across pins 15 and 16 and nothing happened. Then, I replaced the total caps in the PSU and then tried the jumper test again. Success for the PSU repair! The power supply turned on, using the jumper technique, and I measured all the voltages using a multimeter, set on DC measurements.
Once again, the numbers on the pins are located on the wired side of the connector. So, you need to verify that you are on the correct pins before you hook up your jumper. If you are not careful, it is easy to get the pin numbers mixed up. Also, if you trace pin 15, the gray wire, you will see that it goes to the PSU circuit board and the circuit board is labeled on/off right at the point where the wire enters the circuit board. This is a good way of making sure you are on the correct pin, though you would need to open up the case of the power supply in order to verify this.
July 26th, 2010 at 4:37 PM
Hi Jim,
First, thanks for this amazing info you’ve got here for PSU troubleshooting. I’m beginning to test a 661-3350 PSU and am going to start by checking for the correct pin/voltage relationships. I’m looking at the pinout you’ve got labeled for this supply and everywhere that you’ve got the label “gray” or “gray/purple” I’ve got a brown. Everything seems to jive as far as the pattern of colors it’s only the gray that seems to be replaced with brown. Maybe they ran out of gray wire that day in the factory?? Any thoughts?
Thanks in advance.
July 26th, 2010 at 5:46 PM
The main thing is to verify the pins for the jumper.
As far as the colors are concerned, I guess it is possible that the gray wires are now brown on some of the PSUs. Once again, the voltages should still check the same between the appropriate pins.
August 24th, 2010 at 2:23 PM
Hi Jim, Excuse my stupidity, but what does the PG mean on pin number 8? I’m getting around 5 volts on pin 8.
Thanks
Dave
August 24th, 2010 at 4:54 PM
Hi Dave,
In this case, I believe the 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.
So, it sounds like your PSU is saying that the voltages are good, however, I suspect you are measuring this under no load conditions.