iMac G4 15" Flat Panel PSU pinout - please help

Hello, and welcome to the Apple Discussion forum pages!

Sorry that nobody has this information, so far, and the topic is probably
beyond the average user who has done minor hardware upgrades or
replacement of parts in the standard computer configuration; or less.

Thought I'd say hi though - and hopefully you can get that information.
Good luck & happy computing! 🙂

Hey Vadim,
Sorry to be so long in posting this info but it just happens that I had an iMac G4 15" come in that had a bad power supply or so I thought.
On this machine the "white" lead you refer to (black in this particular machine) is supposed to be 12 VDC. The next 4 (to the right) go to a common ground bus in the 2nd part of the power supply that is above the optical drive door. The other two (left) go to the hard drive ground and are all grounded together on the logic board). That other lead (white in your machine) goes to a separate pin. As far as I can tell it is connected to nothing. I can find no continuity on the power supply board to anything. Yours? The blue lead goes to the base of an SMT transistor that is marked Q202. I would expect that to have something to do w/ sleep or start.
As with you I thought this iMac G4 15" had a bad power supply. Now I'm not so sure. It's putting out the 12VDC that's supposed to be there. There's also 12VDC at the anodes of C187 and C197. So that's logic board voltage. So I'm now thinking PMU or general logic board problem. I'll probably give it back to the tech that gave it to me and let him do some parts swaps from another machine.
My symptoms are:
press power
fan comes on
red LED comes on
no chime
no HD spin or boot.
RIchard

Message was edited by: spudnuty

Vadim,
Email me if you need diagrams on the power supply pinouts (incomplete).
Richard

Hello, I jump to this thread while I need some help for my old G4 flat panel which has no power for a while.
It collapsed after my young daughter shut down the I/O of wall socket while it was still in working process. I was aware several hours after, so, when I tried to switch on, nothing has happened at all.
It was unplugged several days before I being able to use the diagnostic test points. I have changed the PMU battery ( which has only 3V instead of 3.6) and followed the service sources to test all this.
Resetting the PMU
No power Led near the reset button.
Made the diagnostic test points:
Test of the battery OK ( of course, it's a new one).
When I have plugged the power cable, I have heard several pulses' noises during 30", then, nothing.
Test of the 3 others points: no power!
the Ac line filter is OK.
I haven't done the n°14 ( i don't understand what to do).
My power supply is dead, I have checked it correctly, no power to the cable connector.
Here is my questions

Even there isn't the 12V needed at the main board test points, does it means that the logic board is defective while the main board can't obtain any power since several days for feeding it?
How to test the logic board without energy?
What happens if the PMU chip crashed?

thank you very much for your help and advices
Nadine

sorry for my english, I'm not experienced with technical's chatting

Hey Nadine and Welcome to Apple Discussions,
First your post would probably get more views if you started a new one rather than being at the end of this one.
That said, exactly which iMac G4 do you have?
So you've done these steps from the service source?
"8. Plug the unit in, but do NOT press the power button. Using a voltmeter, check the voltage from the test point marked “Main” (see graphic above). You should get a reading of approximately 12 volts. If the reading is 12 volts, go to the next step. If you don’t get a 12 volt reading, verify that all the cables are securely connected and test the unit again. Pay special attention to the video cable.
9. Press the power switch on the computer. Using a voltmeter, check the voltage on the test point marked “12v” (see graphic above). You should get a reading of approximately 12 volts. If the reading is 12 volts, go to the next step. If you do not get a 12 volt reading, replace the main logic board.
10. Using a voltmeter, check the voltage on the test point marked “5v” (see graphic above). You should get a reading of approximately 5 volts. If the reading is 5 volts, go to the next step. If you do not get a 5 volt reading, replace the main logic board."
Note especially:

Pay special attention to the video cable.

These have been known to be a problem.

Even there isn't the 12V needed at the main board test points, does it means that the logic board is defective

Do step 15 first. If there is power on the power supply output and none at the "main" test point that points to the logic board.

I haven't done the n°14 ( i don't understand what to do).

"14. Check the connection of the video cable on the LCD flat panel, and try to power on the unit again."
This is checking the LCD connection. There's one on the logic board (careful detaches parallel to the board vs. straight up like all others. There's also another one on the back of the panel. Back has to come off for this check. There have been a few posts about this happening.

Richard

Thank you very much for your welcome and quick answer.
I have an Imac G4 17" 800mhz Flat Panel. Yes, I have done those steps from the Service Source except the 14 step. But now, I have done it, and the connectors are well attached on the board.
The problem is that my PSU is dead but I am not sure that the main board is dead too; unless that someone who knows about repairs, is able to answer to this question:
Does it possible to have 12V measured at the "main" and "12V" test points of the the logic board when the Power Supply Unit is dead?
I ask for, because if I try to change my PSU, I don't want to waste money buying a new logic board if I realize that mine is bad, it isn't worth changing the PSU at all.
thank you for your help,
Nadine

Nadine,

Does it possible to have 12V measured at the "main" and "12V" test points of the the logic board when the Power Supply Unit is dead?

Don't think that's possible since that voltage comes from the PSU. Did you do step 15? If the power supply is dead it would seem to me that an ATX substitution would be easily done since there's only 12V input from the supply. Dunno if that's true but the Service Source only talks about 12V.

Yes, I have done those steps from the Service Source except the 14 step. But now, I have done it, and the connectors are well attached on the board.
My power supply is dead, I have checked it correctly, no power to the cable connector.

Well if the PSU connector shows no power the PSU is dead. Like I said an ATX substitution should be easy.
Richard

Hi Richard,
thanks a lot. Yes, I have done the 15 step and I am sure about the death of the PSU.
But I have no idea of how to install an ATX PS instead of the original one; I don't want to burn anything!
Do you tell that it's possible to only bring 12V somewhere to the power connector of the main? it seems not to be a good way, because the 12V needed at the Test points ( under the main) must have been convert by the main; do I am wrong?
I am a nut with electric stuff;
Do you know the process to install the ATX?
I have search to the forum, but nothing...

thanks 🙂

Man, you made my day. Thanks to your help I was able to revive this iMac a friend of mine gave me. Now I know that the Logic Board is still okay and can look for a spare PSU. Thanks again for posting the pictures !