imac 27 late 2014 crashing / not starting

[SamWijib]

It was working fine until a few weeks ago, then became unreliable. It will be working as normal (not slowing or anything) then suddenly go black with no power, no warning, no freeze, just off like someone flicked the power off at the wall. Then when restarting with the power button on the back, sometimes it refuses to start many times in a row, then for no apparent reason it just starts as normal. I have a midi in out box on one of the USB sockets, which lights up and then instantly off again, every time I press the imac power button, so powering on is being initiated, but then instantly fails.
I've bought the various bits to open it up because I wanted to upgrade the CPU and swap out the hard drive which was reported as worn / failing by a drive diagnostic software. I think I might remove the HDD drive completely and fit a bigger blade drive.

Has anyone experienced this no warning power off and reluctance to start? Any suggestions? (But please don't say 'buy a new mac' - this isn't my only / main imac, and it's not used for running important work software, but it is a very useful internet browsing / shopping / research / zoom / youtube / entertainment machine, so I'd like to keep it going if possible.)

 

[kagharaht]

Try to boot and run hardware diagnostics. Hold down the letter "D" as soon as you turn it on and you will see the process.

 

[SamWijib]

I tried this before, after reading another thread, but it started 'internet recovery' - is that the same thing / part of the process? I gave it the wifi details first and then it seemed to do nothing for about 15 mins, so I rebooted it.
Scratch that, I just tried it again and it worked this time:

No issues found.
Reference code: ADP000

 

[Bigwaff]

It will be working as normal (not slowing or anything) then suddenly go black with no power, no warning, no freeze, just off like someone flicked the power off at the wall. Then when restarting with the power button on the back, sometimes it refuses to start many times in a row, then for no apparent reason it just starts as normal.

You don't mention this... is your iMac plugged into a wall socket, or a surge protector, or UPS surge+battery backup system? It's possible you have dirty power.

 

[ignatius345]

It was working fine until a few weeks ago, then became unreliable. It will be working as normal (not slowing or anything) then suddenly go black with no power, no warning, no freeze, just off like someone flicked the power off at the wall. Then when restarting with the power button on the back, sometimes it refuses to start many times in a row, then for no apparent reason it just starts as normal. I have a midi in out box on one of the USB sockets, which lights up and then instantly off again, every time I press the imac power button, so powering on is being initiated, but then instantly fails.
I've bought the various bits to open it up because I wanted to upgrade the CPU and swap out the hard drive which was reported as worn / failing by a drive diagnostic software. I think I might remove the HDD drive completely and fit a bigger blade drive.

Has anyone experienced this no warning power off and reluctance to start? Any suggestions? (But please don't say 'buy a new mac' - this isn't my only / main imac, and it's not used for running important work software, but it is a very useful internet browsing / shopping / research / zoom / youtube / entertainment machine, so I'd like to keep it going if possible.)

I had pretty much that same iMac (2014 iMac 5K i5) and at one point before I finally upgraded it, I had a spell where it was powering off like that -- super spontaneously and random. I left it with a Mac tech shop and they very kindly left it running for like a week and couldn't reproduce the issue. Turned out it was a bad USB hub. I had some Amazon special generic hub plugged in, and as soon as I removed that from the setup, the issue stopped.

I would recommend running with zero things plugged in to USB for a while, and see how that goes.

 

[kwikdeth]

might want to install some kind of fan/temperature monitoring software, like Macs Fan Control. It will display temperatures in your menu bar. Check out temperatures and fan speeds. Might have a fan on the blink or maybe some thermal paste needs replacing.

hardware test wont necessarily find something that is failing due to heat/age.

 

[SamWijib]

Surge protector - I'm not using one of those, just straight into the wall - I'll try one.
USB - I'll try running without anything plugged in.
I have Macs Fan Control as the GPU runs pretty hot - the main reason for my plan to open it up was to re do all the thermal paste as I suspect it is dried out a bit and also to clean any dust buildup in the fan.

As I gathered the paste and screen stickers, tools etc, my plans grew and I started thinking about what else could I do while I have it open. So I picked up an i7-4790 (not the K version as I think these are still a bit overpriced considering their age, plus the non 'K' version would run a little cooler) and then I started thinking about replacing the blade with a bigger one, as I'd have to get to that side of the main board in order to do the thermal paste.

I don't think it's heat related as the power offs can happen at any time. After a couple of minutes or after over an hour. Plus the non-starting can be from completely cold. Sometimes if it powers off, I can restart it first time, other times it's not having it and I have to walk away.

I suspect the power supply, maybe old caps? Is that a thing with older imacs? I've not read mac threads about that, but I know (in general) electrolytics have a limited lifespan.

 

[Nguyen Duc Hieu]

I suspect the power supply, maybe old caps? Is that a thing with older imacs? I've not read mac threads about that, but I know (in general) electrolytics have a limited lifespan.

If you can afford it, try sourcing for a replacement PSU.
I also guess the issue is lying in the PSU.
Unless you are familiar with computer PSUs, it's not very economical to fix them yourself.

 

[Fishrrman]

"I wanted to upgrade the CPU and swap out the hard drive which was reported as worn / failing by a drive diagnostic software."

Does it have a fusion drive inside?
At 10 years old, at least one component of that fusion drive (SSD or HDD) is probably failing.

You can open it if you want, but be aware in advance of the dangers of doing so -- that is, breaking something while "inside". It's a common occurrence as reported in this forum.

Another way would be to buy an EXTERNAL USB3 SSD, and set that up to become the EXTERNAL boot drive. It won't be quite as fast as an internally-installed SSD, but again, far less risk to install.

Once you're booting externally, you could erase the internal fusion drive, and just "let it be", in place and unused.

 

[ignatius345]

I think I might remove the HDD drive completely and fit a bigger blade drive.

I had a Fusion Drive fail on that same 2014 iMac 5K. The process of sourcing and replacing that blade drive is apparently a bit of work (over and beyond the bit of work just opening it up in the first place). Here's a very comprehesive and well updated thread about it: https://forums.macrumors.com/threads/a-list-of-successful-imac-27-2012-2019-ssd-upgrades.2162435/

What I ended up doing was taking out the SATA HDD and replacing it with an SATA SSD. Very cost effective and very easy once the machine was open. The result was plenty speedy enough, and certainly faster than the Fusion Drive. I know the blade SSD would provide more speed, but you *are* talking about a 2014 iMac that you use as a general purpose auxiliary machine.

 

[SamWijib]

Here's a very comprehesive and well updated thread about it: https://forums.macrumors.com/threads/a-list-of-successful-imac-27-2012-2019-ssd-upgrades.2162435/

Thanks, I'll read through that thread and make some notes - it's pretty big. The power problem is the priority for now - I need to get it stable before working on any upgrades.