I know this is an old thread, but it still comes up in Google searches for the beep sequence of three short, three long, and three short (Morse code for SOS), which is what's happening with the iMac (Mid 2007, 20") I'm working with.
Note that Macs that start up after playing these beeps, and seem to work normally, can still have hardware problems that may corrupt files, including plists that are part of OS X, damage the hard drive's directory, etc., leading to further problems, so you don't want to keep using a Mac that seems to work after playing the beeps--investigate the problem and get it fixed.
My recommended troubleshooting summary/sequence, if you want to diagnose these problems yourself:
Test the RAM. This procedure works with just about any Mac with removable RAM boards; there's some flexibility here in how you proceed, depending on how many RAM boards you have, known-good RAM boards, etc:
- First dissipate any static charge on your body so it doesn't fry your RAM and/or your Mac, by either using a grounded wrist strap, or touching something nearby that's grounded, such as a water faucet (don't assume the ground screw in the middle of an electrical outlet's faceplate is actually grounded), or lacking that, touch a large metal object nearby (file cabinet, etc.). If you need to walk away from the Mac for some reason, when you return, ground yourself again to dissipate any new static charge you've built up.
- Sometimes one or more RAM boards aren't seated firmly, so remove all of them, and then push them back in firmly.
- If that doesn't help, remove all RAM boards, and clean their contacts. I gently use a white eraser, and often also isopropyl alcohol applied with a cloth or paper towel, and then I carefully wipe away any cloth or paper strands, usually with a small, non-static brush. Then, reinstall only one RAM board (or if you're dealing with a really old Mac that requires a minimum of more, install that number).
- If the Mac still beeps, install the same board into another RAM socket.
- If the Mac works (without startup beeps or other problems) when the RAM board is installed in one socket but not another, the logic board may have a bad RAM socket. You can either live with it, and maximize the capacity of the RAM in the good socket(s), or get the logic board replaced.
- If your Mac's existing RAM doesn't work in any socket, try the same tests with known-good RAM.
- If you find any of these RAM-related steps fixes the problem, it's best to doublecheck the repair, by downloading and running a memory testing utility. My favorite is Memtest (from
http://www.kelleycomputing.net), since it's very thorough, but it runs in single user mode, which some people may not wish to deal with, but the author of Memtest also publishes a testing utility named Rember, which you can run from the normal Mac GUI (it's also available from MacUpdate, VersionTracker, etc.).
- If the RAM doesn't seem to be the problem, proceed with the steps below.
CPU chip: problems with the CPU chip can cause errors that seem to be memory-related. If your RAM investigation doesn't implicate the RAM, then if your Mac is out of warranty, before you try the expensive route of replacing the logic board, replace the CPU chip first (if your Mac model has a replaceable CPU chip), ideally with a known-good spare (which unfortunately few people have sitting around). If you don't have a known-good spare, you may have to buy a new one (eBay sellers have some good prices), but you need to know exactly which processor your Mac contains (Merom, Penryn, etc. are some variables, but it can be more complicated than that), and get the exact replacement, or at most the next speed up, which usually won't hurt, as long as the two are of the same type--for instance, you can replace a 2.0 GHz Intel Core 2 Duo T7300 processor, with a 2.4 GHz T7700 processor, since they're both T-type Meroms.
Try a known-good logic board. One problem with replacing the logic board, if you're not doing it through Apple, is that some sources of logic board exchanges will ask you to remove the CPU chip and GPU (Graphics Processing Unit) chip, as well as anything else removable, before you send them the bad board, and you reinstall those parts onto the replacement logic board. If the problem is with the CPU, you'll get the same errors once you install the replacement logic board along with the old CPU, which is why I recommend that, if you're thinking of replacing the logic board through a company that doesn't send a replacement CPU, etc. along with the replacement logic board, that you first investigate the CPU if possible, by trying a known-good CPU on your existing logic board.
Restoring the firmware could be risky if the problems you're seeing are caused by hardware other than scrambled code in the firmware chip, since the bad hardware might cause the firmware restoration process to hang in mid-restore, corrupting the firmware to the point where the Mac is completely unusable, even for a subsequent attempt at firmware restoration. So, you probably should leave firmware restoration as a last resort:
Firmware Restoration CD:
http://support.apple.com/kb/HT2213
