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power supply replaced but still unable to power up.

After the power supply replaced. Plug in power cord the LED #1 is on. Press power button the LED #2 lit momentary follow by rectangular shape LED lit momentary & left lower fan turn on momentary, then the LED #4 Amber light up and stay. Reset SMU by re-plug power cord while pressing the power button no help.

Hardware Overview:

Model Name: iMac G5

Model Identifier: PowerMac12,1

Processor Name: PowerPC G5 (3.1)

Processor Speed: 2.1 GHz

Number Of CPUs: 1

L2 Cache (per CPU): 512 KB

Memory: 2.5 GB

Bus Speed: 700 MHz

Boot ROM Version: 5.2.6f1

Serial Number (system): W85479ANTAR

Hardware UUID: 00000000-0000-1000-8000-001451277FC6

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Once restored all parts, the iMac back to normal & functional. iMac run for 20 minutes latter it switched to sleep mode automatically, and I noticed the back panel very warm, few minutes later it quit. Suspect the cheap heatsink compounds that I applied is not good enough to transfer heat from CPU, may need to use "Cooler Master" compound instead. Anyway let the iMac cool down for 30 minutes then turn it on with an stand fan blow air from the side, now it works for hours with no problem. End up I put one fordable notebook cooling pad aim at iMac bottom grill to help cooling and it works fine even I removed the stand fan away. Through this event I learned always leave the headsink devices and the MCB as one unit, don't disturb it. iMac G5 got cooling issue need to address. Put one notebook cooling pad ( 5VDC / USB ) underneath the iMac it really help. iMac G5 is built with simplicity, so it's easy to T/S and rebuild. I enjoy the process, and thanks all your help.


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Gewählte Lösung

Your machine is overheating somewhere.

LED 1 indicates that trickle voltage from the power supply has been detected. This LED will be ON when the computer is turned off and your power supply is working correctly.

LED 2 indicates that the main logic board has detected proper power from the power supply when the computer is turned on. This LED will be ON when the computer is turned on and the power supply is working correctly.

LED 3 indicates that the computer and the LCD display are communicating. This LED will be ON when the computer is turned on and video signal is being generated.

LED 4 lights only if the computer detects an over-temperature condition. This LED will be OFF when the computer is turned on and running at the correct temperature.

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Apple iMac G5/2.1 20-Inch (iSight) Specs

Identifiers: iSight - MA064LL/A - PowerMac12,1 - A1145 - 2082

I made an error, which I've done before on this machine. It's the transition machine from the G5 iMacs to the Intel iMacs and it's built differently. Also on this machine Apple changed the LED codes. The LED's indicate a bad GPU (video card). This machine also has integrated video. The first thing I would check is the RAM to see that they are a matched pair and seated properly: http://support.apple.com/kb/ht3246


I'm so glad I could be of help. You might want to download and use SMC fan control for the G5 processor (http://custom-css-design.com/node/45148) to up the fan speed. If you haven't remove the CPU fan 922-6992 and make sure the inlet is clear.


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Dear Mayer,

Can I deactivate the overheat sensors or components one by one to isolate the fault source.

Need your suggestion to start somewhere. Do you think that I got faulty main circuit board. Thanks..

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Yes, the Main Circuit board sense the delicate CPU no cooling when I turn on the power. Bcz every time I remove the Main circuit board always removed the cooling devices 1st (It's not necessary to remove the MCB from iMac which is I don't know before. now I learned.) that compromised the heatsink compounds transfer the heat from CPU to cooling devices. After I re-apply the heatsink compounds between the CPU & cooling pads. Installed back the MCB and restored all connectors with finger cross then turn on the power.. Guess what? Yeh.. I'm touch the roof..My iMac back to life! all cooling fans running, the LED #2 is steady ON, & the signature sound out from both speaker.. I'm happy now. Okay let me install back the LCD screen & cover..


iMac G5 Temperatures/Cooling Mod http://www.xlr8yourmac.com/systems/iMacG...


Hardware Monitor is an application to read out all accessible hardware sensors in Macintosh computers.



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In May 2011, Enough with the auto shutdown with chips over temperature and loud cooling fan sound. Re-apply heatsink compound by using the Cooler Master compound inbetween chips and cooler pad. After that restore the iMac then power it up.. WOW.. so quiet the cooling fan run in idle, no more in full speed , CPU temperature around 60 degree C only. even in multi application running the CPU temp. less than 80 degree C..

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DINO WU wird auf ewig dankbar sein.

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