iMac 2010 won't boot into macOS

[Jschut82]

My father's iMac has a very strange problem. When he turns on his iMac, the Apple logo appears and he hears 3 beeps. Then nothing for 3 seconds and then 3 beeps again. This will repeat constantly.

At first I thought of a RAM issue. I have tried with fewer modules and different slots. Even tried every single module in every single slot. All had no effect. If I let out all RAM, I also get 3 beeps but with a black screen.

If I boot into bootcamp then it works fine and Windows works properly. So it seems to me that the RAM is doing fine.

I started the iMac in recovery mode. Disk Utility is there but without an icon. If I want to start it, it won't do anything.

In recovery mode I opened terminal and was able to see the disk. The I copied all the files from the User dir to a backup disk. No problems at all.

When I use diskutil in the terminal it gave me "Ok" on the disk.

Then I thought well let's reinstall macOS. Choose the Macintosh HD. macOS was being downloaded and after the download was finished it jumped back to the recovery mode home screen. Then I tried it again. Same result.

I really have no idea that the problem is here. I did the standard things like resetting NVRAM / PRAM / SMC. All without effect.

Anyone have an idea?

If I want to start diagnostics (d during startup) then I get a globe with an exclamation mark and a 6002D code.

 

[niteflyr]

I would try different memory sticks. The 6002D code points to a hardware issue. This thread may shed some light.

https://discussions.apple.com/thread/4307212

 

[mikehalloran]

3 Beeps is the RAM

https://support.apple.com/en-us/HT202768

On a 2010, matched pairs must be to the right or left vertically. If you followed this picture from the Apple Support site showing horizontal pairs, you did it incorrectly.

If I had not futzed with a 27" 2010 a few days ago, I would not have remembered this.

Only 2 sticks were showing. I did a lot of unplugging and plugging in the process. When I thought I had a bad stick or bad slot, I tried every combination of 2, horizontal and vertical, to see what worked and didn't. I could get 2 sticks to show R or L but horizontal only gave the 3 beeps. Weird that all 4 slots tested good as did all 4 sticks. Inserted all again and everything showed up fine. Sometimes, that's what must be done.

 

[Jschut82]

An update after a lot of trying and testing.

Bought new ram modules and tested them all. 1 module in all 4 slots and both in different slots. All gave me 3 beeps.
All allowed me to boot into windows with no problem.

Put back the original modules. (4 x 2gb) and booted into windows. Windows crashed with a blue screen with a memory issue warning. Second time i could just boot into Windows with no problems at all.

I don't think the memory modules are the issue since i tested multiple modules (including new modules). My best guess now is the memory slots or the logicboard.

Guess it is time for a new iMac

 

[TallManNY]

3 Beeps is the RAM

https://support.apple.com/en-us/HT202768

On a 2010, matched pairs must be to the right or left vertically. If you followed this picture from the Apple Support site showing horizontal pairs, you did it incorrectly.

If I had not futzed with a 27" 2010 a few days ago, I would not have remembered this.

Only 2 sticks were showing. I did a lot of unplugging and plugging in the process. When I thought I had a bad stick or bad slot, I tried every combination of 2, horizontal and vertical, to see what worked and didn't. I could get 2 sticks to show R or L but horizontal only gave the 3 beeps. Weird that all 4 slots tested good as did all 4 sticks. Inserted all again and everything showed up fine. Sometimes, that's what must be done.

Is the same issue at play on the mid-2011 iMac? I've got 12gb comprised of 2x4 and the original 2x2. My iMac is working fine, but maybe I'm not getting all the benefit of the RAM.

 

[mikehalloran]

Is the same issue at play on the mid-2011 iMac?

I don't remember but I'll look at my wife's later today. She has 8x2 + 2x2.