On Jun 17, 2010, at 5:30 PM, Clark Martin wrote: > I acquired an iMac G5 20", no camera (A1076), it doesn't power up. On > plugging in the power cord one diagnostic LED comes on. Resetting the SMC > doesn't help. PRAM battery is good. According to Apple test procedure it's > a bad logic board. One set of caps was blown out, I replaced them (after > much trials and tribulations). All the others looked okay. > > Does anyone know a likely culprit, fix, test? According to the original > owner it was taking more and more attempts (button presses) to start up > before it wouldn't start at all.
The problem very likely is bad capacitors in the power supply, as well as on the logic board. I've gotten the first diagnostic LED to come on in that generation of G5 iMac, which simply means enough power has gotten to the logic board to turn on the light. But after replacing the power supply capacitors (which I got here <http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php>), I got three lights and the iMac booted, even though there were more than a dozen leaking/bulging caps on the logic board. I've also done the same thing and gotten only two lights and some whirring from the hard drive. All the caps on the logic board looked OK, which is no guarantee they're working correctly by the way. After replacing the caps, I got three LEDs and the iMac booted. The caps in the power supply are much easier to replace than those on the logic boards, as you probably know. Make very sure that the replacement caps are soldered solidly to the boards. I examine the soldered legs of my replacements with a magnifying glass while gently wiggling the cap. It's very difficult to get new caps correctly soldered since Apple used lead-free solder with a high melting point during manufacture. As you already know, it's a trial/error/tribulation process. Reviving G5 iMacs can be a real trip. I recently got 4 17-inch G5 iMacs from the tech at the local Mac shop. He couldn't get them to boot and run reliably, so he gave them to me. I got all 4 up and running, even to the point of getting the POST chime. But, one had a bad inverter. One had a bad LVDS cable connector. Two had had only the five 16-volt caps on the logic board replaced. Two had bad power supplies. Two would not pass either Apple Hardware Test and consistently threw video artifacts and reported the same video error, which is typical of G5 iMacs that have suffered internal video chip damage because of bad caps/power supply problems. Long story short, after a lot of parts swapping around I managed to get two solid G5 iMacs out of the four, and those two had all caps replaced on both logic boards and power supplies. So you've got a lot of fun waiting to eat up hours and hours of your life. And all because someone stole an incomplete recipe for capacitor electrolyte from a Japanese company in the early 2000's. What's really evil, though, is that you can't tell a bad cap from a good one. I've had iMacs with obviously bad (bulging tops, leaking electrolyte, tilted because the bottom seal had blown) capacitors on the logic board run just fine. And I've had iMacs with pristine-looking logic board caps fail to boot even with a known-good power supply. Jim Scott -- You received this message because you are a member of the iMac Group, a group for those using Apple iMacs and eMacs. The list FAQ is at http://lowendmac.com/imac/list.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/imaclist
