A "bad logic board" can mean many things; bad processor, bad graphics chip, bad something else; on the iMac G5, all major components save for the power supply are integrated straight into the main logic board. On the non-iSight G5 iMacs, swollen or leaking caps was a common symptom, but even if the caps are fine, that doesn't automatically mean the logic board is all fine and dandy. Bad boards don't always have physical defects you can see with the human eye.
Lastly, the most common reason an iMac G5 won't start is due to a bad power supply; in fact, I've never seen an iMac G5 even with swollen caps not start due to a bad logic board. I've replaced PSU's on iMac G5's with swollen and leaking caps that afterwards booted just fine, power wise.
Did you replace the caps on your G5's logic board?
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You can replace the capacitors in the power supply (secondary side). It's about 15$ of parts and an hour of work or less with decent soldering equipment.
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wow if its not one thing its another i got the PSU issue resolved i now get led 2 coming in and the fans/cd and hdd going but now i am not getting led 3 and i dont even have gong.
any idea's i was thinking maybe its the LCD but wont i have the gong to indicate that its wokring, i tried the option+cmd+P+R key i have PC keyboard so its windows+atl+P+R but i dont get anything, does it look like im down in my luck and its a logic board issue?