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View Full Version : imac G3 700mhz start up problems power supply




thehumble1
Dec 1, 2008, 11:15 AM
System: imac g3 700mhz graphite. 2x 256mb SDRAM. OEM 60gb HD, OEM CDRW optical. The only thing changed from stock is the addition of the extra stick of RAM.

Symptoms:

on startup you hear the drive kick in the cd start to spin and the CRT power on, then a click and everything powers off. the screen blinks and there's a small, fading, red star in the middle as the CRT blinks off.

after that I can't get anything from the unit till I unplug it and wait 5 seconds. when I plug it back in, I hear an electronic click and I can repeat the process ad nausium.

BUT:

If I disconnect the Hard Drive power supply the computer doesn't fail immediately on boot and I can get a host of other problems depending on what's connected.

CD connected
HD connected
HD power disconnected

I hear a partial "gong" (mac startup sound) and drives spin up. light comes on at power button, image never comes on, sometimes shuts back off sometimes stays like that. No image on external monitor either.
_______________________________
CD connected
HD disconnected
HD power disconnected

hear almost all of the gong sound then the same as above.
________________________________

CD disconnected
HD disconnected
HD power disconnected

full startup gong sound, no video on internal or external.

USUALLY the above happens but I have gotten other results:

for a while everything was working fine, but the system was hanging as if the hard drive had problems. I never saw the ? folder, but the system would not boot and just hung at the apple symbol.

On CD I was able to get OS X install to boot up and run system profiler.

Occasionally I can get the hard drive to spin up by connecting the power supply after boot.

It really seems as if there is a large resistance or a lack of voltage to the system. As if starting the CRT and the hard drive and logic board at the same time is creating too much draw.

I've reset the PMU and sometimes it changes how much of the gong sound I hear, but not much.

It seems like it's either the P/A/V board or the down converter for the logic/drives, but I'm not familiar enough with these systems to know which. I do know that the problems have gotten progressively worse and I also know that the hard drive runs fine when installed in an external drive enclosure. I think I could try booting it without the internal drive attached, but I'm wondering if there is no video because it's running hardware checks and not booting if there is no internal drive.

Any ideas or thoughts? Thanks.