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Sick iMac - keeps restarting

H

Happy Marsden

macrumors member
Original poster
Sep 5, 2014
44
5
I have a 2007 20" iMac that was working perfectly. Then I turned it off, and carried it into the adjacent room. The power cord got caught on the door handle as I entered the room. The iMac fell to the floor, from about the height of the door handle. Not that hard, as I had a bit of a grip on it, and nothing was visibly damaged....

However, after turning it on, it would no longer work! What is happening is, the fans spin for a few seconds, and so does the DVD drive. They shut down for a couple of seconds, then start up again, and this repeats infinitely! The display is black, and does not come on any longer. There are three diagnostic lights lit up. Which means the mobo is no longer talking to the display. Which means any solutions that involve the keyboard, such as SMC resets, are a no go.

I've partially disassembled the machine. I can find no visible damage. The hard drive has been verified to work okay, so it wasn’t damaged. I’ve removed the display, checked the cables for damage (there was none). Reinstalled it. No difference. Pressing in the Power button for 10 seconds does cause the fans to go full speed, and one long beep. Other than that, this solution fixes nothing.

I can’t understand why this iMac has gone haywire, and won’t work any longer, after such a relatively small bump. And I can’t find any info anywhere, on this particular issue. Does anyone have a clue as to how I might fix this?
 
Yes, I agree. Try replacing the PRAM battery.
Be sure to reseat the RAM sticks. Swap the RAM between the slots, and check to carefully seat that RAM.

You did not say what happens when you try a PRAM (NVRAM) reset...
Do you now get a boot chime, even one that sounds distorted?
It may not be getting far enough into the boot sequence (the POST) to reset, and the video working shouldn't really affect that, if the rest of the hardware is working. (video should not affect keyboard response, assuming the boot sequence is getting that far.)
If you do get any kind of boot chime, continue to hold the same Option-Command-P-R until you get two more chimes, then release the keys to check if the video then does anything.
(some of us just like the tinker, just to get that "old guy" working successfully. Nothing to do with a waste of time, and I might just decide to kick in a little money, just because it's an old computer that I think deserves to run another day or two.
(That's kinda the idea about OCLP in the first place :cool: )
 
Chuckeee: Check the power cord socket on the back of the iMac.

I did try a different power cord, to no avail. But it can't be that, since the iMac isn't dead. Since it's fans do start up and shut down, repeatedly.

DeltaMac:

I did swap out and reseat the RAM, using just one module, in different slots. No change. Don't have an extra battery on hand, I don't think, to test out the PRAM battery. They're kind of hard to get. But in any case, it could not possibly be dead, since the iMac had been working fine for weeks, until 20 seconds before I dropped it. I did push in the battery, just in case it might have moved from the drop. But it hadn't moved.

I did say in my OP that I cannot try keyboard based solutions, like NVRAM reset. Because the machine does not get far enough into the boot sequence, to where it will recognize keyboard commands. ie. It doesn't make the Apple boot chime. It just spins the fans and Superdrive on and off, repeatedly. Screen is black.

Fishrrman: Yes, I know there's a lot of "ageism" in the Apple community. Where people are conditioned (by Apple of course), to constantly buy new hardware. And to believe older hardware is useless junk. But I don't buy that line, and I don't follow the Pied Piper. This 2007 iMac was set to last a good 10 years more. I had it set up with both El Capitan, and the latest Linux Mint. So it could do streaming, any web site, light video editing, light games, word processing... basically what most people do on computers. I had planned to give it to my grand daughter.... twenty seconds before I dropped it!
 
Yes, a BR2032 can be challenging to find locally.
But, if a low or dead PRAM battery is the issue (and it's possible), then a CR2032 (much easier to find) is likely to get you going again, and you can replace with the (better) BR2032 after you locate one.
 
Happy Marsden said:
Where people are conditioned (by Apple of course), to constantly buy new hardware. And to believe older hardware is useless junk. But I don't buy that line, and I don't follow the Pied Piper. This 2007 iMac was set to last a good 10 years more. I had it set up with both El Capitan
Click to expand...
I'm typing this on a 2008 iMac... and I understand. I even agree with the sentiment.

But things do eventually break.

Especially if we drop them.

Planned obsolescence has been the philosophy of the industrial era post WWI.

Try the battery replacements recommended above and report back.
 
I checked the battery today, it is 2.9x volts - so it is fine. It's socket is also fine. But again, it can't be the battery is dead anyway, because the iMac was working great, 20 seconds prior to dropping it only 3' off the floor. So whatever happened, obviously occurred from the drop itself. But as I said, the drop wasn't hard enough to produce any visible damage or broken cables or connectors I can see, anywhere inside or out. And I checked that no cables are disconnected.

So far, the only real clue I have is the 4th diagnostic light is off, indicating the mobo isn't talking to the display. But the display is not cracked, and all its cables are intact. So I've no reason to think it's not working.
 
When you try to boot - does the screen stay completely black, or is there any kind of dim glow from the screen, and not fully black. Best to look in dim room light for this glow.
 
Yes, the screen stays completely black, no glow. I think whatever powers it on, is just not doing that.

Anyway, I am giving up on this, and will have to dump the iMac at a recycling centre. I disassembled the entire thing, and tried powering it on with only the motherboard, power supply, one RAM module, and one fan. Everything else, including wifi module, HD/DVD drives, and even the battery, was removed. No change. It still powers on a few seconds, powers off for a couple, then repeats the process. If I depress the power button a few seconds, then I make the fans go on full. But that's all that changes.

Still have no idea how a small drop can do this much damage... but I guess it will remain a mystery. But when you consider the complicated sensor system, and how many things can go wrong on an iMac, it's not that much of a mystery....
 
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