diagnostic lights and a possible bad Power Supply

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iMac G5 20" Model A1076

1.8 or 2 GHz G5 processor

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gsimsfla @gsimsfla

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Posted: Nov 7, 2012

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diagnostic lights and a possible bad Power Supply

I think mine is a 2005 model of the PowerPC 20". It's a 20 without the ISight so EveryMac points me at the '05. Does this model come equipped with the diagnostic lights as the newer ones do? If so, what might possibly indicate A bad power supply compared to other components?

Is there a good reference for Apple POST tests and indicators? book or website.

Thanks everyone.

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LikeARabbit @likearabbit

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Posted: Nov 7, 2012

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What are the symptoms you're experiencing with your iMac?

The iMac G5s were notorious for having bulging and/or blown capacitors, which often led to power issues, video issues, freezing issues, etc. A quick inspection of the capacitors on the logic board and inside the power supply (use a flashlight once it's removed) can give you a quick answer in most cases.

I don't have a G5 iMac in front of me at the moment so I'm going off memory. With the back cover removed there should be 4 LEDs visible, just below and centered between the two fans. With the power cord connected (be VERY careful not to touch anything while power is present!) LED 1 should be lit green, assuming the power supply is good. When the power button is pressed LED 2 should light. When video has been properly established LED 3 will be lit. LED 4 is a temperature warning, it should be off in a no trouble found scenario.

Hope that helps!

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Thank you. My problem is this. We bought if from Ebay for our daughter to mess around on. It booted well 4 or 5 times and she put in several hours into working on a typing tutor. It was running fine, good clear display, quiet whirring fans and responsive in it's operation. one day It was running for about half an hour so my girl could work on it when she got home. When she got on it the system was dead. We thought it was stuck in sleep but it was dead, no display, no fans, nothing. The LED on the left is lit and steady but no other signs of life. If it were CMOS I would think it would power up but not keep the time and date current. If it is the logic board I would think the LED would not light up. A bad HD would power up but just sit lit up with the blinking folder. The plug does make a minor spark when I plug it into the wall outlet. That and the one LED are the only things it does now. I don't know whats next. I have no way to check the RAM except to buy and try. Any advice is greatly appreciated.

Thanks.

Nov 7, 2012 by gsimsfla

The failed capacitor problem I mentioned before can show itself in several ways, one of which is a steady sleep LED on the front of the machine with no other signs of life. That model is fairly straight forward to open up (lay face down on a flat surface, loosen 3 screws along the bottom, tilt the rear housing up), I would remove the rear housing and check for bulging and/or leaking capacitors.

You can kinda check the RAM... While the back cover is off you can remove both RAM DIMMs and attempt to power the machine on with the RAM installed. During the POST process Macs run a basic check on the RAM, giving the normal chime if it passes the RAM and other tests. However, if it fails to detect RAM or finds a fault with RAM it will give a very distinct loud beep. 3 beeps means no RAM found, there are other combinations as well though they aren't helpful here. If the iMac's behavior doesn't change when the RAM is removed then that's another strong indicator that the logic board is at fault.

Good luck!

Nov 8, 2012 by LikeARabbit

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Thank you. My problem is this. We bought if from Ebay for our daughter to mess around on. It booted well 4 or 5 times and she put in several hours into working on a typing tutor. It was running fine, good clear display, quiet whirring fans and responsive in it's operation. one day It was running for about half an hour so my girl could work on it when she got home. When she got on it the system was dead. We thought it was stuck in sleep but it was dead, no display, no fans, nothing. The LED on the left is lit and steady but no other signs of life. If it were CMOS I would think it would power up but not keep the time and date current. If it is the logic board I would think the LED would not light up. A bad HD would power up but just sit lit up with the blinking folder. The plug does make a minor spark when I plug it into the wall outlet. That and the one LED are the only things it does now. I don't know whats next. I have no way to check the RAM except to buy and try. Any advice is greatly appreciated.

Thanks. — gsimsfla
The failed capacitor problem I mentioned before can show itself in several ways, one of which is a steady sleep LED on the front of the machine with no other signs of life. That model is fairly straight forward to open up (lay face down on a flat surface, loosen 3 screws along the bottom, tilt the rear housing up), I would remove the rear housing and check for bulging and/or leaking capacitors.

You can kinda check the RAM... While the back cover is off you can remove both RAM DIMMs and attempt to power the machine on with the RAM installed. During the POST process Macs run a basic check on the RAM, giving the normal chime if it passes the RAM and other tests. However, if it fails to detect RAM or finds a fault with RAM it will give a very distinct loud beep. 3 beeps means no RAM found, there are other combinations as well though they aren't helpful here. If the iMac's behavior doesn't change when the RAM is removed then that's another strong indicator that the logic board is at fault.

Good luck! — LikeARabbit