iMac G5 17" model A1058 dead

This mac simply stopped dead, no previous symptoms whatsoever. Diagnostic LEDs indicated faulty logic board (#1 lit, #2/#3/#4 off). Replaced logic board with refurbished one, but with no effect (LEDs same as previously). So my question is - could the problem be the power supply? In others words, could LED#1 light even if there was insufficient power getting to the logic board? If this is the case, would it be worthwhile purchasing a used working power supply? (the refurb logic board wasn't too expensive, but I'm reluctant to spend much more on an old computer if there was no certainty I could get it working)

Update

yes, I did enable the PSU with the jumper pins as indicated in the article you mention.

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After you replaced the logic board, what does it do on start-up? What LEDs light up?

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It doesn't start up - no fans, no hard drive spin... nothing. And only LED#1 lights up - the same as it did before I installed the new (refurb) LB.

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From the G5 17" (non iSight) manual

• 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.

Assuming I am reading the manual correctly, If LED1 is ON then the PSU is at least powering up to some degree. Check THIS PINOUT guide or THIS ARTICLE and see if the other voltages are present. Note the instructions to power ON the PSU while not connected. THIS ARTICLE may also be of interest

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+ nice addition of the pinout(s) to verify the voltages.

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thanks for the pinout guide. I checked the PSU with a voltmeter, and for sure it is dead (the only voltage reading I obtained - 5.1v - was on the pin indicated as purple on the guide).

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Did you enable the PSU by jumper pins 15 (gray) and 16 (blk/gnd). This turns the supply on as per the other LINKED ARTICLE The +5V on the purple wire is the Standby Voltage and will be the only voltage present until the PSU is told to power up.

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That probably confirms the PSU is dead.

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@richdave: I haven't had an opportunity to try it with an external monitor, but I will do so when i can. The PSU I connected to it was from a working machine and I had to put it back after checking. I've since bought a working PSU on ebay, when this arrives (it'll be a couple of weeks as I'm in Australia & the PSU is coming from the US) I'll install it and then see how the machine goes with a friend's external monitor. I'll post the result here.

@adlerpe: I installed a new PRAM battery with the logic board replacement, but checked it again anyway - it's fine, 3v.

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If just #1 lights up, this indicates a faulty power supply. I have no idea why you replaced the logic board. This model had a lot of issues with bad capacitors so I would inspect them for corrosion and or swelling.

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I replaced the logic board after following the sequence of steps on Apple's iMac troubleshooting site: <http://support.apple.com/kb/ht2173> which indicated the problem was with the logic board - but as the replacement achieved nothing, I'd have to agree with you in that the problem is in fact with the PS. But I'd also appreciate your comments on Apple's troubleshooting site above.

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LED 1 lights from a trickle charge coming from the PSU. Basically it indicates the unit is plugged in and the PSU has power. I believe the guide provided by Apple is wrong. LED 2 indicates that the logic board has detected all the proper voltage from the PSU. Typically it will blink if the PSU is weak and can't handle the current draw required to power on. However if the PSU is failing to produce some voltages it is impossible for LED 2 to light. I understand why you replaced the logic board, based on Apple's published troubleshooting guide for the problem. Instead of replace logic board for no LED 2, LED 2 also doesn't blink, it should have stated verify PSU voltages, if they are correct replace logic board. If they are not correct, replace PSU.

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ABC I agree the Apple troubleshooting is not specific enough but it is not aimed at self repair, its aimed at filtering out the bad power cable, smc reset etc. If those things don't fix it, you're supposed to let Apple fix it.

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You're right the advise from Apple contradicts my experience and is not very clear. The LED quotes that we gave are from a book called "Desktop and Potable Systems", Second Edition and is in the Apple training series for techs. Sometimes I think Apple writes for techs that have all the spare parts sitting in boxes in front of them and are doing warranty work without regard for costs.

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I've replaced the PSU and now the machine starts up - I get the chime, the hard drive spins and I get 3 LEDS lit... but NO display; screen stays completely dark. Any suggestions as to cause and remedy?

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