iMac 20in makes three beeps and fails to boot?

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Level 1

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iMac 20in makes three beeps and fails to boot?

I have just changed the hard drive on my previously working 20in Intel iMac. The drive was pre-formatted and loaded with Mountain Lion using an external dock. The computer functions when fire-wired to another iMac, showing the doners desktop. Now I hear three intermittant beeps when pressing the start button on the 20in iMac. The screen remains dark. (It is assembled, but I have not fitted the aluminium front bezel or the glass yet). It does not respond to any keyboard commands. The memory moduls have been re-inserted firmly. Help please?

iMac, OS X Mountain Lion (10.8.5)

Posted on Jan 31, 2014 7:13 AM

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Answer 1

Klaus1

Level 9

52,749 points

Jan 31, 2014 7:33 AM in response to Macintosh30

Sounds like a RAM problem:

Beeps on startup:

1 beep = no RAM installed

2 beeps = incompatible RAM types

3 beeps = no good banks

4 beeps = no good boot images.

5 beeps = processor is not usable

http://support.apple.com/kb/HT2538

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Answer 2

kostby

Level 4

2,940 points

Jan 31, 2014 7:37 AM in response to Macintosh30

99% certain that's a RAM error.

I just added RAM to my mid-2011 iMac, and one of the modules was defective:

At power on, dark screen and 3 beeps.

I removed all the memory modules (four 2-GB modules) and tried again, just one module at a time to find the bad one.

My mid-2011 with OS X 10.8.5 will boot just fine with only one 2GB module installed. Wouldn't want to RUN any apps with it that way, but for testing, it's fine.

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Answer 3

Macintosh30 Author

Level 1

0 points

Jan 31, 2014 7:40 AM in response to Klaus1

Hi Klaus1,

I thought it might be the memory RAM so refitted them firmly. The modules were the original working ones and I took care to strap to earth whilst handling them?

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Answer 4

Macintosh30 Author

Level 1

0 points

Jan 31, 2014 7:48 AM in response to Macintosh30

Hi All,

I removed each (of the two) modules in turn, and leaving only one in place, the now Mac boots up fine! It is currently busy installing the loaded OS 10.8 and I've cleaned the contacts on the uninstalled RAM, hoping to fit it later. I'l eep yopu posted whenit is complete. Thanks!

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