iMac display

A 2017 27-inch iMac getting a second life as a 5K display. The computer inside comes out, a controller board drives the original 5K panel, and the iMac's own speakers and fan setup stay.

Status: In progress
Donor: 2017 27-inch iMac with a 5K Retina panel
Controller: JRY-W9RQUHD-SA1 display driver board
Inputs: DisplayPort, USB-C and HDMI
Kept: The original speakers and fan setup
Hookup: One Thunderbolt cable for video, monitor control and charging
Mounts: Printed parts I found online, plus custom parts I designed
Skills: Hardware teardown and rebuild, display interfaces (DisplayPort, USB-C, USB4), power conversion, troubleshooting and pinout tracing, CAD and 3D printing, iterative prototyping

The back of a silver iMac with a black braided Thunderbolt cable plugged into a USB-C port where the Ethernet port used to be, beside three gray printed buttons in the old USB slots. — One Thunderbolt cable into the plug I designed for the old Ethernet hole, next to my printed menu buttons.

The open iMac chassis lying on a workbench, with a silver mesh power supply mounted at upper left and the two black speaker housings on either side. — Inside, with the computer gone: the new power supply in place and the iMac's original speakers back in.

The goal

My monitor is a 27-inch Apple Thunderbolt Display: only 2K, with no modern inputs. Apple has used nearly the same 27-inch 5K panel since 2014, first in the 27-inch iMac through 2020 and now in the Studio Display, which costs well over $1,500 as just a monitor.

I picked up a 27-inch 5K iMac for about $200 and bought the parts to turn it into almost the same thing, for a fraction of the price.

How it works

I'm taking the computer out of the iMac and replacing it with a JRY-W9RQUHD-SA1 controller board, which drives the original 5K panel from DisplayPort, USB-C or HDMI. The iMac's own speakers and fan setup stay, with a 24 V-to-12 V converter feeding the fan controller. The new board and its connections are held by a mix of printed parts I found online and custom parts I designed.

The empty iMac chassis on a workbench, with the black speaker housings and the fan lying on the cutting mat in front of it. — Stripped down: the logic board and power supply out, with the speakers and fan set aside on the bench.

The empty iMac chassis with a silver mesh power supply mounted at upper left. — The new power supply going in on printed supports.

Credit where it's due: the controller board holders are maikisch's remix, for the 2017 iMac, of StoneTaskin's original design. The crossover and step-down converter mounts and the fan vent are montezemolo's design, and the power supply supports are professorshroom's. All of them are linked below.

Key decisions

One cable, like a Studio Display. I designed a secure plug that fills the hole left by the iMac's Ethernet port and holds a right-angle USB4 connector wired to the board's input. One Thunderbolt cable from my MacBook to the back of the monitor carries video and full control of the monitor, and charges the MacBook over USB-C Power Delivery.
Menu buttons in the old USB holes. Custom buttons I designed fit where the iMac's USB ports were, with a holder for the controller's button board behind them, so I can use the board's on-screen menu without modifying the outside of the case.
Keep the iMac's speakers and fan setup. The display keeps the iMac's sound and cooling instead of relying on the board's own.

Close-up of the iMac's back edge: a USB-C port set into a gray printed plug where the Ethernet port was, under the original Ethernet icon. — My printed plug in the old Ethernet hole, holding the USB4 port.

Close-up inside the iMac's lower edge, showing a gray printed part seated behind the old port opening. — The plug from inside the case.

The back edge of the iMac with four gray printed buttons in the old USB slots, beside the headphone jack and SD card slot. — Printed menu buttons in the old USB holes.

Problems and fixes

The power converter didn't fit its mount. The 24 V-to-12 V converter for the fan controller was smaller than the mounting holes on the printed part I'd downloaded for it. I got two of its corner posts screwed down, and since it's a lightweight board, two screws were enough.
I fried the fan by trusting the internet. The iMac's fan doesn't use a standard computer fan plug, and its wires aren't in the standard order. I wired it to the fan controller in the order someone had posted online, and it was wrong: the fan died. Since it was already dead, I cut it open to trace the real pinout: VIN, GND, O/P and PWM. I wired the replacement fan in that order, and everything worked. Lesson learned: verify a pinout yourself before trusting a forum post.
The buttons took a dozen tries. It took almost a dozen revisions to get buttons that fit the old USB holes and a holder that lines the controller's button board up behind them.

Where it is now

Most of the conversion is done. I'm now designing how to hold the ports from the inside before I have the RAM door cover laser cut.

The back of the iMac with a black printed panel in the RAM door opening, holding several display and USB ports, above the power cord. — Work in progress: a printed panel holding the board's ports in the old RAM door opening.

What's next