View Full Version : G4-Sawtooth intermittent failure to start--no power

06-18-2003, 11:12 AM
A friend has a G4 Sawtooth that has performed flawlessly until recently. Now it occasionally refuses to start, with no light on the power or monitor button, no fan noise; and in all respects it acts like there's no power. Most of the time it does start right up. Once or twice it has started and run for a while, then it goes out, and later comes back on by itself.
He took it to the local certified Apple shop, but they were unable to get the computer to reveal it's comatose side, despite leaving it on for several days
If it powers up, then it will usually run fine, with no apparent software problems. Does anyone have any suggestions for diagnosing this problem? The Apple tech apparently could not find a problem when the computer was running. Is there some way to isolate the problem when the computer is in its comatose mode? Could a loose connection be the culprit? Is it worthwhile to replace suspected parts until the problem is resolved? What parts are the most likely suspects?

06-18-2003, 11:23 AM
Start with a new battery and go from there. Radio Shack or OWC or most any supply store.

OWC 3.6v (http://eshop.macsales.com/Catalog_Item.cfm?ID=2524&Item=OWCMAC36V)

06-18-2003, 05:15 PM
A long shot, but here is a tip from another user (Boots):
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>
Apple Support gave me an interesting suggestion and new debug technique I had not been aware of, and I figured I'd pass it on.

I had already booted from the Apple Hardware Test CD and run all the tests in quick and extended modes. No problem found.

The tech suggested to run the extended tests, hit CTRL-L, and you'll see "Loop Mode On" in the lower panel. Run the extended test overnight in this loop-mode to see if it finds a failure and reports a failure code.

It might catch a problem which occurs only after the machine has been running for a certain amount of time, or related to heat. The Tech said this is one of the first things they'd do anyway at the shop.

She also said that it runs out of Open Firmware of the CD and doesn't involve really anything else, so this is an excellent diagnostic for determining and pinpointing failures. She said it might come up with a code (which is usually somewhat meaningful) and it might point to a specific component, or the video card. If there's a problem with the motherboard, it should show up this way. <HR></BLOCKQUOTE>

No idea if it would even help with a power issue...but could not hurt, right?


Charlie Don't Surf!

06-22-2003, 06:49 PM
We tried replacing the battery, and the problem persists. I will try unclemac's diagnostic suggestion. What an annoyance. Does anyone else have any ideas. I should add that an SCSI PCI card was installed a long time ago, which, as a wild guess, I am going to try removing.

06-23-2003, 09:18 AM
By all means, remove everything that you can to eliminate variables.

Reminds me of about a half dozen imacs we had that had problems with sticky power buttons....with some the users had mashed them in so hard that they got sideways and lodged in the case, and with others the hole in the case that the button travels in was just too snug. Either way, if you breathed on the machine wrong it would shutoff all by itself, cause the power button was being engaged continuoulsy. Just like pushing and holding for a hard shut down. Once we freed up the actual buttons so they floated loosely in the case, the mysterious shutdowns wet away.

I wonder if it is possible that you are having a simialr problem, or maybe the power switch behind the button could be going bad?

I have no electrican skills, but it seems like it would not be too hard to test/verifiy the power switch and switch circut. If you can rule out all other hardware (PCI stuff, etc.) that would leave the power swich, the PS, and perhaps the MB right?


Charlie Don't Surf!

06-23-2003, 09:36 AM
?Do a PMU reset. The Power Management Unit controls power on, shutdown, sleep and motherboard memory functions. While shutdown press the little (tiny) button on the motherboard next to the battery ONCE. Wait 20 seconds before powering up.

?I've never heard of the PMU causing quite this problem, usually the power button lights up for a second then goes black. But hopefully this gets it.


<font size=-1>Quis Custodiet Custodes Ipsos?</font>