27-inch 5K iMac 2014, 2015 and 2017: Upgrades, Repairs and Specs

The 27-inch Retina 5K iMacs from Late 2014 to 2017 are among the easiest Intel iMacs to upgrade. Memory goes in through a door on the back, and every one of them has both a 3.5-inch drive bay and a PCIe SSD slot, so an SSD and extra RAM make a big difference for far less than a new iMac. The exception is the screen: a replacement 5K panel usually costs more than the whole iMac is worth, and we will say so. We do the work at our workshop near Castle Hill.

This page covers the Late 2014, Mid 2015, Late 2015 and 2017; our iMac repair and upgrades hub covers the rest.

How to tell which 5K iMac you have

About This Mac, in the Apple menu, shows the full name, for example “iMac (Retina 5K, 27-inch, 2017)”. For the Model Identifier, hold Option, open the Apple menu, choose System Information and read it from Hardware Overview.

The model number under the foot of the stand is less helpful than people expect. A1419 is printed on every 27-inch iMac from Late 2012 to 2017, including the non-Retina 27-inch 2012 and 2013 models, so it gives the size but not the year. The EMC number beside it narrows things down, and the serial number, entered at checkcoverage.apple.com, settles it.

The Late 2014 and Mid 2015 share the identifier iMac15,1 and EMC 2806. The Mid 2015 was the lower-cost model, with a 3.3GHz i5, Radeon R9 M290 and a plain hard drive; the Late 2014 has a 3.5GHz or faster processor and a Fusion Drive as standard. Both are treated the same for RAM and macOS.

5K iMac specs, 2014 to 2017

All four shipped with 8GB of RAM.

Upgrades

RAM through the rear door

Press the small grey button just above the AC power port and the memory cover comes away, exposing four slots. There is no display removal and no adhesive, which is why a 27-inch RAM upgrade is from $329 with 16GB fitted, and fitting memory you have bought yourself is from $89.

• Late 2014 and Mid 2015: 32GB maximum.
• Late 2015: Apple says 32GB, but OWC sells and certifies 64GB as four 16GB modules.
• 2017: 64GB on Apple’s memory page. OWC has certified 64GB in every 2017 27-inch, including the 3.4GHz model Apple’s spec sheet lists at 32GB. Reports of 128GB conflict, so we treat 64GB as the ceiling.

The 2017 takes DDR4 and the earlier models DDR3, so check your Model Identifier before buying modules.

SSD: two places to put one

Unlike the 21.5-inch models, every 5K iMac here has a PCIe blade SSD slot on the logic board, whether or not it was ordered with flash storage, alongside the 3.5-inch SATA bay. Both routes need the glued display removed first. Our SSD upgrade is from $599 with 500GB or from $699 with 1TB, including data transfer and macOS setup.

• SATA SSD in the 3.5-inch bay. Apple’s factory drive supplies temperature data to the iMac that a retail drive does not, so without an in-line thermal sensor the fans run at full speed and Apple Hardware Test reports a failure. A sensor or fan-control software solves it, and we handle it as part of the job.
• NVMe SSD in the blade slot, through an adapter. Owners report success on iMac15,1, 17,1 and 18,3. The iMac needs macOS High Sierra or later installed first, so its firmware can boot from NVMe. On the Late 2015, users report that the iMac cannot wake from normal sleep with a third-party NVMe drive; the cited workaround makes the Mac hibernate instead. We talk this through before choosing a drive.

Fusion Drives in this group carry little flash. The 1TB Fusion in the mid-range Late 2015 has 24GB, and the 1TB Fusion standard on the 2017 has 32GB; everything beyond that lives on the hard drive. Replacing either half splits the Fusion into two drives, and rejoining them wipes the data, so your files are copied off first.

macOS: Apple’s limits and the patcher

Those limits matter day to day. Chrome’s last versions were 138 for Big Sur and 150 for Monterey, and Microsoft 365 no longer updates on any of the three. Ventura, on the 2017, still runs current Chrome but has had no Apple security update since August 2025.

OpenCore Legacy Patcher moves all four models to Sequoia, the highest macOS it supports. What to weigh up:

• Security is relaxed for good: System Integrity Protection is lowered and the system volume’s seal is broken.
• Patches must be put back after each macOS update. Some Sequoia installs need internet access to fetch support files for this, and graphics acceleration is missing until it is done.
• Updates download as full copies of macOS, and going back to an older version means erasing the drive.
• Sequoia’s Apple security updates should end around September 2027 on past form, and there is no Tahoe release of the patcher.

Our install is from $249. The process, and which apps need which version, are covered in newer macOS on an old iMac.

Faults and gotchas

• Fans roaring after a drive change. If a previous drive swap has left the fans at full speed, the missing temperature data described above is the first thing we check.
• A slow, tired original drive. APFS was designed mainly for SSDs and loses performance on a hard disk over weeks and months, which is why an older 5K on its original drive can crawl. See why an iMac runs slow.
• Screen damage. Glass and LCD are laminated together, so a crack means a full 5K panel, from $1,099 fitted (see iMac screen replacement). Read the numbers below first.
• A screen that will not hold its angle. We repair 27-inch hinges from $299. Apple’s hinge repair program covered only Late 2012 and Late 2013 models and has expired.
• No power. A 27-inch power supply is from $479 and board-level repair from $449, and the $150 bench diagnostic is waived if you go ahead with the repair. See logic board, graphics and power supply repair.

What is worth paying for

Working Late 2015 5K iMacs were advertised on Gumtree in September 2026 at a median of about $400 (seven listings, $350 to $650), and 2017s at about $475 (six working listings, $400 to $599). Faulty 2017s were listed at $200 to $249. There were too few Late 2014 and Mid 2015 listings to give a figure.

The screen is where the numbers fall apart. The 5K panel alone retails for about $745 from an Australian parts supplier, and our fitted price is from $1,099. That is nearly three times the asking price of a working Late 2015 and more than twice that of a 2017. Unless your iMac has upgrades you want to keep, buying a working one is far cheaper than fixing the screen.

Memory and storage are a different case. From $1,177, a 2017 on its original Fusion Drive gets a 500GB SSD, 16GB of RAM fitted and Sequoia. That is about half the $2,399 for a new 24-inch M4 iMac, and you keep the 27-inch 5K screen, but it is more than twice what a working 2017 is advertised for. Weigh it as the cost of keeping a machine you like against the cost of replacing it; on a 2014 or 2015 that case is much harder to make. The wider picture is in repair or replace an old iMac.

Bringing your 5K iMac in

iMacs are drop-off only, Monday to Saturday from 8am to 6pm, at our workshop near Castle Hill. Customers bring them from across the Hills District and Western Sydney, including Parramatta and Blacktown. SSD and RAM jobs usually take one to two business days when parts are in stock, and every repair has a 12-month warranty on parts and labour.

Get a quote

Next generation: the 27-inch 5K iMac 2019 and 2020. Smaller screen: the 21.5-inch iMac 2015 to 2019.

Questions

Can I use a 5K iMac as a monitor for my laptop?

Not through Target Display Mode, which no Retina 5K iMac supports. The workaround is a driver-board conversion, where the iMac's internals come out and a third-party board runs the 5K panel as a standalone screen. The board alone costs about $449 in Australia, which can make sense for a 5K iMac with a dead logic board and a good panel when a new Apple Studio Display is $2,599.

Will 128GB of RAM work in a 2017 27-inch iMac?

It is not something we would rely on. One owner reports four 32GB modules running stably in an i7 model, while another tester found only 64GB usable. Apple's memory page lists 64GB, and OWC certifies 64GB in every 2017 27-inch. We fit up to 64GB in the 2017, eight times what it shipped with. The 2020 is officially rated for 128GB, and OWC sells 128GB for the 2019.

Why are my iMac's fans running at full speed after an SSD upgrade?

On 27-inch iMacs from Late 2012 to 2019, the original hard drive reports its temperature to the iMac. A standard SSD or hard drive in the 3.5-inch bay does not, so the iMac assumes the worst and runs the fans flat out, and Apple Hardware Test flags a failure. An in-line thermal sensor or fan-control software fixes it. We can sort it out even if someone else did the upgrade.

Can a Late 2015 iMac 27-inch run macOS Sequoia?

It can, through OpenCore Legacy Patcher, although Apple's own support ended at Monterey. The Late 2015 needs the patcher's Legacy Metal graphics patches, which work but leave some gaps, and Sequoia's security updates are expected to end around September 2027. Fit an SSD first, because patched Sequoia on the original hard drive or Fusion Drive will be slow. Our patcher install is from $249.

Can I upgrade the RAM in a 5K iMac myself?

Yes. Shut the iMac down, unplug it, press the grey button above the power port and lift off the cover to reach the four slots. Buy modules that match your Model Identifier: DDR3 for the 2014 and 2015 models and DDR4 for the 2017. If you would rather not, we fit memory you supply from $89, or supply and fit 16GB from $329.

Is a 5K iMac with a cracked screen worth anything?

Not much. Faulty 2017 27-inch units were listed on Gumtree at $200 to $249 in September 2026, against about $475 for working ones, and a replacement 5K screen is from $1,099 fitted. Before you sell one, have the data copied off and the drive erased. If the iMac still starts and enough of the screen is visible, you can do both yourself.