iMac Model A1419 order No. MF125LL/A replacement drive

The Fusion Drive uses both an HDD and a PCIe blade type SSD. Replacement of either is not straightforward and is an "advanced" job that requires a near total teardown of the computer. The PCIe blade-type flash drive is mounted on the underside of the logic board (rear facing).

The hdd part of the Fusion Drive is a typical 3.5" desktop class drive. The hdd can be replaced with either another 3.5" hdd or a 2.5" laptop class drive (hdd or ssd) with adapter. In both cases there is also a temperature sensor that must be replaced to keep the cooling fans happy. (not required if only replacing the PCIe SSD)

If you choose to do this replacement, I'd suggest that you ask your tech to remove both internal components of the Fusion drive and replace the hdd with a standard ssd. Drives, installation kits and guidance are available here.

Though your young user may be "tech- and wires-averse" I suggest the better option still may be to simply use an external drive for startup on this very vintage Mac. The setup of an external drive is super easy with no potential for internal damage to the Mac.

The internal drive(s) in the 2013 iMac can be replaced, but the wisdom of spending the money and time to do so is questionable. Opening the iMac will expose critical parts to accidental damage.

A better option is simply to use anSSD in an external drive case, format and install macOS onto it and use that as the startup drive. Performance will be similar to that of the internal drive and you won't risk any additional damage to the iMac. When your computer has reached its end of life you can then continue to use the drive with the next computer you get.

Please see this helpful tip by user @Jack-19: Use an external SSD as your startup disk … - Apple Community

Also, it may be possible to repair the split fusion drive. Apple provides this guidance:

How to fix a split Fusion Drive - Apple Support

Finally, you might wish to run the DriveDX utility by binary fruit to discover the overall health of the drive(s) in your iMac.

In case you're wondering about replacing: macsales.com vids

Angus McC wrote:

Thank you v much for all those useful alternatives. The idea about using an external drive as startup makes great sense, likely cheaper and safer than replacing the internal drive. The young user in my family, however, is tech- and wires-averse 🙄😂 and the appeal of the computer has always been its compact, uncluttered design and er sleek 'form factor'. I'm also acquainted with a reliable non-Apple technician who has economically performed Mac repairs for me in the past.

So just to check: A standard SSD is fine as a replacement for the original 'fusion' ? I may have to go that way to keep the youngster happy... 😂🙄 – we're good on mem, maxed out at the 32.

While this sounds like a noble endeavor to keep the youngster happy, it can actually be a curse.

1) It will cost as much or more than the iMac is worth to upgrade it internally.

2) It can not run anything later than the unsupported macOS Catalina 10.15.

3) It can not download and run any of the latest App Store App's or Games.

4) Worse it may have serious trouble interacting with his school web-site.

To put it in simple terms, the youngster may become discouraged by not being able to run newer software or games and quickly loose interest.

With that in mind, I would get and run it from an external SSD as suggested by D.I. Johnson, while considering a new iMac or Mac mini and external display for the youngster.

To add to my previous posts, I hope you have been using some backup strategy. Whether Time Machine, Carbon Copy Cloner or other, it's imperative that you have backup of your personal files and info that has accumulated on this computer. Computing without a backup is a guaranteed way to lose data, especially when your computer is vintage or obsolete.

You're welcome.

Please update us on your solution.

+1

You're welcome.