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#1 2017-06-18 02:32:09

Registered: 2017-06-18
Posts: 1

G4 won't start. Fan runs but no bong and no gray screen.

I sure could use some help.  My wife just loves her old 20-inch G4, which was booting up and displaying files just fine until today. After moving it from our condo (which we are shutting down) to our regular home, I cannot get it to display anything.

Pushing the power button causes the black screen to flicker for a moment, after which the fan runs and (sometimes) a green light displays in the lower right corner, and (sometimes) pulses for a while.

But I never get to the gray screen, and hear no sounc (though the speakers are plugged into their porta0.

I welcome any suggestions for reviving this old beauty. My wife is very attached to it, and it would mean a lot to her to have it working again.

-Brooks Jackson


#2 2017-06-18 18:44:29

Registered: 2017-06-17
Posts: 20

Re: G4 won't start. Fan runs but no bong and no gray screen.

Any way way to reset it ?, been a long time since i  messed with an Imac (it's an Imac G4 right ?)

Try to reset the PMU first, then remove the bottom and replace the battery if that doesn't work. … ery/7030/1

Another known issue is a PSU failure.


#3 2017-06-19 02:35:04

From: Corvallis, OR
Registered: 2014-05-12
Posts: 1,022

Re: G4 won't start. Fan runs but no bong and no gray screen.

Can't remember if it is the same for iMac G4 but the AGP Powermacs would turn on with fans and not boot if the PRAM battery was dead. Removing or replacing it would allow it to start.

Daily Drivers: 27" iMac 2.8 GHz Quad-Core i7 (Late 2009), 21.5" iMac 2.7GHz Quad-Core i5 (Late 2013), 11" Macbook Air 1.6 GHz i5 (Mid-2011)
See the restored heroes here.


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ThinkClassic specialises in the use, maintenance, repair, restoration and modification of vintage computers and peripherals.