On Feb 6, 2011, at 9:39 PM, Amanda Ward wrote: > > On Feb 4, 2011, at 7:39 PM, Clark Martin wrote: > >> >> On Feb 4, 2011, at 6:51 PM, Amanda Ward wrote: >> >>> Hi All... >>> >>> A problem with my iMac G5... 1st Gen, 20 inch, 1.8 GHz, 1 GB ram, 500 GB >>> HD, Airport Ext., Bluetooth. I think that's about it. >>> >>> The problem... a while back it started going into sleep when playing videos >>> (with VLC). As time went on, it seemed to take less and less time for it to >>> do so. Now it is shutting down every time I try to start it up. Gets to the >>> spinning wheel and then just *blink*... it shuts down. >>> >>> The person I got it from told me the power supply had been replaced. Just >>> wondering if the Pram battery could be bad? >>> >> >> I got a dead iMac G5 from a client. I started by looking at the logic >> board. It had a number of bulging caps on it, this is a known problem. I >> replaced all of them and then some. Still woudn't start up. I looked in >> the power supply and it too had some bulging caps. I replaced some of them >> but I ran into some troubles with it so I ended up buy a rebuilt supply from >> e-Bay. Once I put that in it booted right up and has been fine ever since. >> >> So based on that I would have a look at the caps on the logic board. You >> can find take apart instructions at www.ifixit.com. Once you take the back >> off you can see if the caps are bulging. There are a couple of dozen all >> told in a group roughly at the bottom center (going from memory there). >> They are cylinders 3/4" high by 1/2" diameter (very rough dimensions). If >> some of them are bulging that is likely your problem. >> >> If you know how to solder you can replace the bulging ones I replaced all >> the caps in each group if just one was bulging. It's bit tricky as they are >> soldered in with lead free solder, it has a higher melting point than leaded >> solder. If you don't know how to solder (this isn't the time to learn) >> maybe you can find someone who can. >> >> Clark Martin >> Redwood City, CA, USA >> Macintosh / Internet Consulting > > Thanks to Clark and Jonas for their responses!!!! > > I did some trouble shooting. First of all the capacitors look fine, no bulges > or leaks. On the mainboard the led's (three of them) light up before the > system shuts down. However, starting with the internal power switch, the > system starts up and keeps running. THEN... starting with the external switch > again, it keeps running. (Insert picture of confused person scratching head!) > > The new problem... it gets to the grey Apple logo with the spinning widget > and just stays there. After a bit the fans shift into high gear. > I've reset the pram and nvram. Tried to start up from the Leopard dvd holding > down the c key, but nope. Tried booting holding down the "Option" key... > still nothing. > I can get into open firmware. but I can't get it to boot
Have you tried booting from the Apple Hardware Test, or from an Apple Service Diagnostic disk (IIRC, ASD 2.5.7 or 2.5.8 works with G5s)? Your problem is that the boot sequence is dying or freezing right at the point the third LED (which indicates the system is talking with the LCD) lights up. Shutdown or freezing occurs because your iMac can't handle the transition from low video demands during grey screen booting to high video demands during blue screen final booting. This is a very common occurrence with iBooks that have the video chip issue. I'll bet that the AHT or ASD will throw a video error and stop. AHT and ASD run using low video demands, as does Open Firmware. What you're experiencing may be bad capacitors that don't let the video circuitry perform to capacity. I know, they may not bulge, leak or tilt, but they can still be faulty and not handle full-boot/running loads. The bad caps can be on the logic board, or as Clark found, on the power supply board. Or, in several cases I experienced, on both. I've followed Jim Warholic's advice/experiences and successfully recapped boards and power supplies: <http://jimwarholic.com/2008/07/how-to-repair-apple-imac-g5.php>. I've also recapped iMac G5 boards and power supplies with no success, probably because of damage inside the multilayered boards caused by previous arcing and component failures, or by improper capacitor removal/installation (my fault). It's a bear of a job to melt the high-temp, no-lead solder used on those boards, especially sucking solder out of holes or if a lead breaks, thus leading to damage. My attitude is that the boards are already dead, so if I revive them, it's OK, and if I really, really kill them, I tried. I've also found that improper shutdowns or restarts after freezes cause corruption of parameter memory. So my standard practice when trying to sort out an iMac G5 or iBook G3/G4 with video-related boot problems is to do an Open Firmware reset with every start attempt, if at all possible. (Command, Option, O, F, then three lines of instructions: set-defaults, reset-nvram, reset-all with each line followed by a tap on the Enter/Return key.) Good luck. Trying to zero in on what's wrong with a G5 iMac is one of the most frustrating tasks a Mac hobbyist can face. Jim Scott Macs for Kids Eureka, CA -- 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 imaclist@googlegroups.com To leave this group, send email to imaclist+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/imaclist
