View Full Version : G4: possible power supply issue?

08-07-2001, 05:19 PM
Yesterday I tried to turn on my G4 Dual450 (model M7892LL/A), and had absolutely NO response.. NO bong.. NO light in the power switch (not even a quick flicker). I moved the power cord to two different outlets, and even tried a different power cord. I verified that the outlets did indeed work. Still no power to my computer. I kept trying off and on for several hours but with no success. I made sure that the battery was still properly seated. I pressed and held the button next to the battery. I tried pressing the reset switch, and opened the case and tried to wiggle the housing around the power button, and also made sure the ribbon cable was still attached to the power button housing. Still no power. I turned off the switch on the power strip and went to bed.

This morning I powered the strip again, and without moving any cables, I pressed the power switch on my computer, and BAM!, it started right up. I cycled four or five times, and it came up each time.

My question(s): could I have an intermittent problem with my power supply? Is anyone aware of any issues with power supplies in these machines? Do I need to insist that Apple replace my power supply before I loose my standard one year warranty in a month and a half?

And by the way, regarding Apple's warranty service: I called Apple today to inquire about getting a warranty replacement, but they wanted to CHARGE me in order to "troubleshoot" the issue first, to which I said "NO THANKS." I don't like that policy of having to pay in exchange for someone to ask me if I'm sure I have the power cord plugged in!! What kind of warranty concept is THAT?

Any insight would be appreciated!


[This message has been edited by jb (edited 07 August 2001).]

08-07-2001, 10:58 PM
I've had several front panel boards fail on this series. This is a little board that has the power button/LED, reset button and interrupt button. Unplug that ribbon cable from where it attaches to the logic board. Wiggling it or reseating the cable will do nothing when the board's fully failed.
Then use a USB keyboard (one with a power button) to turn the G4 on or off.
If THAT doesn't work then it may be the P/S, but you would need to test for trickle current with a multimeter first...
Either way, take the G4 into a service provider so they can replace the bits under warranty!

08-08-2001, 12:09 AM
Apple will not charge for the diagnostics if it proves to be a warranty issue. The charge is their protection against those that would call daily forgetting to turn on their powerstrip.

08-08-2001, 12:53 AM
Ya, the charge is for those bone headed questions the techs get everyday. We all do it occasionally, but if you have a real issue there is no charge under warranty.

I have seen what tachyon is talking about. The early ADC G4 systems had issues with the power on button. Eventualy the power on button would fail and eventually the board would fail. You can visually verify that your system is one at risk.

Power down the system.
Open the case.
Look at the video card connector. Near the back you will see a 3 prong transistor. On this will be a resistor - that looks like it was soldered on at the last minute. I wish I had a picture.

If this is what you have then your system is at risk. You will really need to run it until the power on switch is dead or the main board is dead. We have had two mobo replaced due to this issue, but we have 8 other systems like this that are not having the issue yet. The local Mac authorized service center has stated that they have replaced over 50 such boards. While I do not think the failure rate is all that high when compaired to the Windows/x86 world - it is fairly high when you look at Apple's track record.


Life in the fast lane leads to:
The Resteraunt At The End Of The Universe

08-08-2001, 05:25 AM
Wow, thanks for the info. This is good to know. I'm looking and I don't see what Dragon is talking about. I really don't know what I'm looking for.. I too wish you had a photo! I'm a bit confused: Is this on the video card, or on the main board itself near the PCI slot connector? On the main board, just above the video slot there appears to be a resistor but it is sitting on top of what seems to be a seven pin black square thing (that has JM03AG on top of it). I don't see any three pin transistors which have a resistor on top, but I am not an electronics genius, so I could be staring right at it and not know. Maybe though, the fact that I don't see anything like that is a good sign?

Since the thing seems to be working today, maybe I'll just keep going with it and decide if I need to buy the Apple Care option before warranty expires. I'd just hate for it to go down at a critical time with no warranty. Since it is working at the moment, would a service center even do anything if I took it in now, or would they have to see it in failing mode to replace anything? Thanks for your help!


08-15-2001, 02:17 AM
ask your Apple dealer to email you the pictures from:

Power Mac G4 (Gigabit Ethernet): Troubleshooting No Power
TIL-SP Article ID:58742

The article was for service providers only so you wont be able to get in.

If the logic board has this resistor you mention AND you have had startup problems then you have rights to have them replace both the logic board and front panel board simultaneously as described in the above TIL article. Buy the AppleCare anyway or plan on selling the whole thing when the warranty expires. Service parts are ridiculously expensive, particularly if they are nonstandard such as processor cards or logic boards.

[This message has been edited by tachyon (edited 17 August 2001).]

08-21-2001, 03:01 AM
Thanks, Tachyon. You were right: I can't get to that til article. I'll have to see if I can get Apple to send it to me. I purchased the AppleCare extension on the web at the online Apple store on August 8, and they are still "assembling" my order. Humm. I've called twice to check on this order, and they still tell me that they seem to be low on warranties right now, and they are waiting for a new shipment to come in. Wow. So when I get it, I'll call in as a certified Apple Care customer, and then perhaps I can get somewhere.

Thanks again for the help!

hubba bubba
09-05-2001, 08:22 AM
Have to second the power switch/LED board diagnosis, seen that more than a few times myself.