G3 blueberry iMac 350MHz switching off problem

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I have a G3 blueberry iMac that unexpectedly turns itself off after it's been switched on for a while. Once it's turned itself off, the power button stays green and flickers. If I leave it for a while, it will power up again as normal. Please could someone explain what the problem could be? Thanks.
 
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Your Mac's Specs
Silver M1 iMac 512/16/8/8 macOS 11.6
Sounds like you are having a hardware problem and perhaps in the power supply.
 
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MacMini 14.3, 8.1 & 4.1, OS 13.5, 10.14, & 10.11 & 10.6; Macbook Pro 8.2, OS 10.12.
I have a G3 blueberry iMac that unexpectedly turns itself off after it's been switched on for a while. Once it's turned itself off, the power button stays green and flickers. If I leave it for a while, it will power up again as normal. Please could someone explain what the problem could be? Thanks.

Couple of questions:
1. How long is "a while"? Is there an overheating issue? Your iMac may be shutting down temporarily to cool off. Check too that the air intake vents at the base of the iMac aren't clogged with dust, and that the air outlet vent is not blocked by something.
2. Are you using a UPS or surge protector? If so, check that the operational light on either unit is on and, if possible, test the power supply therefrom.
 
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Hello, Thanks for replying. The mac shuts down after several hours use. I think you are right that it is either an overheating issue or power supply. If I leave the iMac for say 5-10 minutes I can power it up again, and it works normally. So I think overheating is a strong possibility. When it turns itself off it briefly makes an unusual sound, after shut down. It sounds a little like Captain Kirk beaming down from the Starship Enterprise. Maybe he's stuck inside and that's the problem!!! The monitor screen has developed a slight tick every so often too. I am not using a UPS or surge protector.
 
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Adrian it may be worth running Apple Harware Test over the machine. If you do not have a copy for iMac, v. 1.2.2, download from the link and drag the .dmg file to the left hand column in Disk Utility and burn on to a CD.

The CD will be bootable by holding down 'C' on startup:-

http://www.info.apple.com/support/aht.html

Struth I loved my iMac 350 with its 10GB HDD and CD-RW optical drive but they are fair cows to crack open and do any work on!
 
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I tried to run an Apple hardware test from the Mac OSX 10.3.9 disk that I am currently running on the iMac. It told me that my computer was incompatible with the Apple hardware test. Any other ideas on what I could try?
 

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