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User profile for user: Jonas2005
Jonas2005 Author
User level: Level 1
13 points

imac mid 2011 21,5 inch keeps crashing

Hello forum,

I have a big big issue and normally i am the techie nerd but now i have no clue what to do next.

Every 3 min my mac crashes this has been going on for a couple of weeks now it is worse and i am unable to use the iMac. here is a bit of the mac history:

the cable of the internal drive broke so the former owner (familie member) of my mac had someone come over to fix it (i was six back then so i dont remember) it now runs with a external drive LC-POWER USB 3.0 HDD enclosure. At first it was on sierra then i updated it using dosdude catalina. that was not smooth so i downgraded it to High Sierra. From that moment the issues started. I deleted the whole hdd again inclusive the EFI partition and reinstalled. for a week i did not have any isssues what so ever but yesterday it began again i moved the imac to the side because i was stressed so i wanted to game a little (i have to computer and it might sound spoiled but it because i want to split work and free time it helps me concentrated at my work the imac is my work machine and i have a game pc wich is not smart to say in a apple forum:) the reason for moving is i have one desk and not a very big room. anyway i dit a smc and the other reset dont remember what it is called tried to download sierra from the app store to reset it to a state i never had a problem that dint work because it froze again. eventually i got a file and tried to make a bootable sierra usb that dint work ether because it froze i dont no how to fix it even safe mode crashed . i cant do anything on the mac the cpu ram and disk are fairly low so that is not issue please help someone remember i have pc to use as assistence for some kind of download or something.


edit after crashing it restarts and does not give any info what so ever

iMac 21.5", macOS 10.13

Posted on Apr 6, 2020 2:12 AM

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User profile for user: Allan Jones
Allan Jones
User level: Level 9
72,104 points

Posted on Apr 6, 2020 1:01 PM

This could be part of the problem:


it now runs with a external drive LC-POWER USB 3.0 HDD enclosure.


The 2011 iMacs do not have USB3 ports so an external USB drive will be incredibly slow. It may be timing out.


Speed data:


  • The old internal drive was either a 5200 rpm or 7200 rpm, 3000MB/s SATA model connected to a 6000GB/s drive bus.
  • The USB2 ports with which all 2011 iMacs are burdened have a MAXIMUM transfer rate of only 480MB/s, about one-sixth of the max possible rate of the factory internal drive. And that speed would assume that the external drive contained a fast SSD! A mech drive on a USB2 port would be close to unworkable for booting.


I do not think this is surmountable with your current layout. Your best option--if you want to keep it in service--is to open up the computer, deal with the data cable, and replace the current factory internal hard drive with a 6GB/s SSD. You'll need a kit that includes the important temperature sensor cable and a drive holder. That would give you ~500MB/s based on my experience, compare to more more than 100-110MB/s for the factory drive when it was working.


This is the other problem:


then i updated it using dosdude catalina.


That likely made changes to the boot volume that are not working when you try to go back. As that is an unsupported hack, I recommend you contact that that developer for his suggestions on reverting/recovering from the attempt to use his product.


That said, I must admit I had a lot of trouble getting useable information from your post. The lack of paragraph breaks and capitalization made it hard to read on a screen. It is possible I misread something. If so, I apologize in advance.


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User profile for user: Allan Jones
Allan Jones
User level: Level 9
72,104 points

Apr 6, 2020 1:01 PM in response to Jonas2005

This could be part of the problem:


it now runs with a external drive LC-POWER USB 3.0 HDD enclosure.


The 2011 iMacs do not have USB3 ports so an external USB drive will be incredibly slow. It may be timing out.


Speed data:


  • The old internal drive was either a 5200 rpm or 7200 rpm, 3000MB/s SATA model connected to a 6000GB/s drive bus.
  • The USB2 ports with which all 2011 iMacs are burdened have a MAXIMUM transfer rate of only 480MB/s, about one-sixth of the max possible rate of the factory internal drive. And that speed would assume that the external drive contained a fast SSD! A mech drive on a USB2 port would be close to unworkable for booting.


I do not think this is surmountable with your current layout. Your best option--if you want to keep it in service--is to open up the computer, deal with the data cable, and replace the current factory internal hard drive with a 6GB/s SSD. You'll need a kit that includes the important temperature sensor cable and a drive holder. That would give you ~500MB/s based on my experience, compare to more more than 100-110MB/s for the factory drive when it was working.


This is the other problem:


then i updated it using dosdude catalina.


That likely made changes to the boot volume that are not working when you try to go back. As that is an unsupported hack, I recommend you contact that that developer for his suggestions on reverting/recovering from the attempt to use his product.


That said, I must admit I had a lot of trouble getting useable information from your post. The lack of paragraph breaks and capitalization made it hard to read on a screen. It is possible I misread something. If so, I apologize in advance.


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imac mid 2011 21,5 inch keeps crashing

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