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Mac Forum / General / Hardware / September 2004iMac makes crackling noise
Someone gave me an older iMac which won't start up. Pressing the power button, you hear the system wanting to start but after three or four seconds, there is a slight crackling noise and everything goes dead. If you press the button again, nothing happens. After a couple of minutes, you can try another start with the power button but with the same results. What is causing the crackling noise and why does it cause the iMac to go dead? Thank you for your assistance. > Someone gave me an older iMac which won't start up. Pressing the power > button, you hear the system wanting to start but after three or four [quoted text clipped - 6 lines] > > Thank you for your assistance. I'd try the power lead first, these are quite common for failing. Otherwise it sounds like a dead PSU.  SignatureAndy Hewitt ** FAF#1, (Ex-OSOS#5) - FJ1200 ABS Honda Concerto 16v: Windows free zone (Mac G5 Dual Processor) http://www.thehewitts.plus.com - now online > > Someone gave me an older iMac which won't start up. Pressing the power > > button, you hear the system wanting to start but after three or four [quoted text clipped - 9 lines] > I'd try the power lead first, these are quite common for failing. > Otherwise it sounds like a dead PSU. I think it's the hard drive that's gone south. I've seen it a few times at work on the iMac 350 and 400 generation (7 GB and 10 GB disks). A helpful company was able to restore the contents of the disks to new drives for equivalent of $200 each time (plus the price of the new disk). <Snipped Text> > > > Thank you for your assistance. > > [quoted text clipped - 6 lines] > drives for equivalent of $200 each time (plus the price of the new > disk). Yes, they do die too. I had to replace the one in ours, although it just started getting badly corrupted. SignatureAndy Hewitt ** FAF#1, (Ex-OSOS#5) - FJ1200 ABS Honda Concerto 16v: Windows free zone (Mac G5 Dual Processor) http://www.thehewitts.plus.com - now online > <Snipped Text> > > > > Thank you for your assistance. > > > > > > I'd try the power lead first, these are quite common for failing. > > > Otherwise it sounds like a dead PSU. This sounds like a power supply problem, or some component causing an over current condition. A 'crackling' sound is often associated with the high voltage section. Having said that, I would try reset the PMU (Power Management Unit) AFTER checking the battery voltage, which should be 3.3 to 3.7 volts (if not replace the battery). Disconnect the AC power, then press the power management reset button (a small [usually red] button on the same side of the logic board as the battery close to the RAM slots. Press the reset button ONCE only, wait 10 seconds before connecting the AC power cord. It that fixes it -- great. If not the problem is not the PMU. > > I think it's the hard drive that's gone south. I've seen it a few times > > at work on the iMac 350 and 400 generation (7 GB and 10 GB disks). > > A helpful company was able to restore the contents of the disks to new > > drives for equivalent of $200 each time (plus the price of the new > > disk). This does NOT sound like a HD problem at all. A dead HD will fail to boot and produce a flashing '?' on the screen. A dead HD also will not stop you from booting from a bootable CD while holding down the 'C' key. > Yes, they do die too. I had to replace the one in ours, although it just > started getting badly corrupted. Signature-Ernie- "There are only two kinds of computer users -- those who have suffered a catastrophic hard drive failure, and those who will." Have you done your backup today? > > <Snipped Text> > > > > > Thank you for your assistance. [quoted text clipped - 5 lines] > over current condition. A 'crackling' sound is often associated with > the high voltage section. Or the head failng to read the disk. > > > <Snipped Text> > > > > > > Thank you for your assistance. [quoted text clipped - 7 lines] > > Or the head failng to read the disk. Agreed, but that shouldn't cause the computer to power itself off again, rather you should get a flashing '?'. But I have seen enough strange problems to never say never. It is possible that a bad HD is drawing an over current causing the PSU to shut down. A quick check is to pull the (4 pin) power plug on the HD and try to start up. If the "same try to start, then shut down" happens, the problem is NOT the HD. If it doesn't shut down but you get the flashing '?' then the HD indeed is the problem. Signature-Ernie- "There are only two kinds of computer users -- those who have suffered a catastrophic hard drive failure, and those who will." Have you done your backup today? > I think it's the hard drive that's gone south. I've seen it a few > times at work on the iMac 350 and 400 generation (7 GB and 10 GB > disks). A helpful company was able to restore the contents of the > disks to new drives for equivalent of $200 each time (plus the price > of the new disk). A dead hard drive won't prevent the computer from turning on. With a dead hard drive, the iMac will power on and you'll see a flashing question-mark icon in the center of the screen. The OP's report about crackling and complete failure sounds like a power supply issue to me, or one of the high-voltage boards directly connected to the PS. -- David >From: Ernie Klein <eckleinspammenot@pacbell.net> >This sounds like a power supply problem, or some component causing an >over current condition. A 'crackling' sound is often associated with [quoted text clipped - 9 lines] > >It that fixes it -- great. If not the problem is not the PMU. I put a new battery into it and noticed that there isn't even a hard drive (the former owner removed it). I pressed the CLCA Reset button (I think that's what printed near it) and waited for, at least, 15 seconds and then reassembled the iMac and plugged it in. Same problem. I may have pressed the button several times in trying to find it (it's pretty tiny). Does that matter? The screen stays dark but the power button lights up, the light in the cd drive lights up, I hear a slight humming as if it's powering up and about 3-4 seconds later, a crackling (fizzling?) noise comes from the back of the computer and the power shuts off. Pressing the power button avails nothing. I have a system cd which I was going to use to see if it would boot to a desktop. Once I ascertain that it's, at least, working, I will invest in a hard drive for it. Thanks for everyone's help so far. Note- disassembling and reassembling this thing is a pain. > From: Ernie Klein <eckleinspammenot@pacbell.net> > >Apple says that is does. That pressing the button more than ONCE can >crash the PMU chip... > >Good luck, I wish I could be of more help. You've been a lot of help so far. I've learned a lot more than I normally would. I removed the battery for 10 minutes, pressed the button once and waited to try it again. Same result. I took the motherboard into a shop today to test and they had a iMac similar to mine. They swapped my motherboard into their iMac and it booted fine so they said my PSU mightt be cooked. I can't afford to have them look at it though as they charge an arm and a leg, They did the test swap for free. I guess I have a bad PSU (like you suspected) or something like that. Ah, well. Sal, the old gal :) |
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