iMac G4(K)

posted on february 26th, 2025

with tags
hardware,
mac, and
retrocomputing

last updated on march 5th, 2025

A year ago I tried using an M1 iMac for work duty but its 21″ screen took up too
much room on my desk.
After seeing
Sean’s video on Action Retro
about putting an M4 Mac Mini inside an
iMac G4,
I thought I’d give it a try.

Trying the Juicy Crumb DockLite G4
The
Juicy Crumb DockLite G4
replaces the main logic board in a 17″ or 20″ iMac G4 and turns its built-in LCD
into an HDMI monitor.
It also uses the iMac’s custom power supply and has a built-in audio amplifier
to be able to drive the
Apple Pro speakers
that were available for the iMac G4.
Swapping the boards is easy and completely reversible.

iMac G4 1GHz logic board and DockLite G4

I ordered the DockLite G4 but it was going to take a few weeks to get.
In the mean time, I needed to find a 17″ iMac G4 in good condition but not fully
working so that I wouldn’t be sacrificing a working machine.
I eventually found one on eBay and I paid nearly as much for shipping as the
machine itself.
The iMac uses a lot of thick steel inside the dome which makes it quite heavy.

Pro tip: there are a bunch of 17″ G4 iMacs on eBay that are listed as 15″.
I don’t know if it’s because eBay fills this in by default or if people are
confused by the screen size since it measures about 15″ horizontally but the 17″
refers to its diagonal size.
It’s usually possible to tell which size it is by the photos since the 15″ looks
much more square, but if you can get the serial number on the bottom,
looking it up
will confirm whether it’s 15″ or 17″.

Once the dead iMac arrived, a power-on test produced a happy chime but showed
nothing on the screen.
At this point I wasn’t sure if the LCD was busted or if the problem was with the
iMac’s logic board, so I had to get a
Mini VGA to VGA adapter
to test its video output.
This also failed to show any video so I was pretty sure the logic board was
faulty but I still had no idea whether the LCD worked.

Eventually the DockLite arrived from Australia and after a few minutes of
swapping things, I was able to confirm that the LCD worked fine and was
displaying the Mac Mini’s desktop over HDMI.

iMac G4 with DockLite G4 connected to M4 Mac Mini

Unfortunately after using the iMac for a little while, I noticed a few issues
that soured my experience with the DockLite.

Color Banding
I’m not sure whether the DockLite or the 20-year old LCD screen is to blame for
this, but there is noticeable color banding on the screen, especially with macOS
window shadows.

Color banding in window shadow

I wasn’t able to test native Mac OS with the iMac’s logic board so I can’t be
sure the problem isn’t with the LCD, but I’ve seen this same problem with some
other generic
LVDS/eDP to HDMI
boards.

iMac Screen Resolution
My other issue with using the iMac G4 was that its 17″ screen has a resolution
of only 1440×900.
This isn’t terrible but having used 1.5x or 2x resolution screens on my
laptops
for many years, the small resolution was not ideal and modern macOS is
definitely not tuned for 1x resolutions anymore.

Exposed Ports
It’s a very minor gripe, but I would have liked some sort of covers to fill in
the space between the DockLite’s new ports (or lack thereof) and the iMac’s
bottom case cutouts.
No one’s going to see them anyway but for the money, it would have been nice to
have that included.

DockLite ports

Screen Blanking
However, my biggest issue with the DockLite is that it doesn’t support turning
off the display via HDMI (DPMS or CEC or whatever this is).
When the Mac Mini tries to blank the screen after inactivity, the DockLite keeps
the backlight on showing a black screen.
Juicy Crumb warns about this in the documentation saying to tap the power button
on the back of the iMac (which pushes the power button on the DockLite board)
to turn off the screen since leaving it on all the time will damage it.
This was going to get pretty annoying since I would like to leave the machine on
all the time but I wouldn’t be using it very often, so I would like the display
to turn off and back on automatically when I need it.

On the upside, the DockLite does support adjusting the LCD’s backlight level
via USB through a
custom macOS application
rather than having to press the buttons on the back of the iMac.

Upgrading the Screen
With these faults in mind, I decided to ditch the DockLite and go with a custom
screen upgrade.
With a different LCD and appropriate driver board, I could get a higher
resolution with better color and gain screen blanking.
By eliminating the DockLite, I could then remove the iMac’s internal power
supply which otherwise takes up a large portion of the upper part of the dome.
That would then free up enough room inside the iMac to store the Mac Mini
without modifying it (as Sean had to in his YouTube video).

Browsing eBay, I found the
Sharp LQ170R1JX42,
a 4K 3840×2400 17″ LCD originally used in the Dell XPS 17.
This would provide a 2x resolution of 1920×1200 in the same outer footprint of
the iMac’s original LCD and fit behind the screen bezel.
An appropriate
eDP driver board
would connect the LCD to the Mac Mini over HDMI or USB-C.

LQ170R1JX42 with eDP driver

Once I confirmed the new LCD and driver worked with the Mac Mini, I disassembled
the iMac to swap its screen.
The original LCD is quite heavy and is about 1/2″ thick due to its CCFL
backlight.
The new LCD with its LED backlight is so light and thin, I didn’t even bother
making a frame to attach it to the bezel, I just secured it with tape and then
mounted the controller to the back of it.

iMac screen with original LCD

Bezel with screen removed

New LCD mounted in bezel

Controller on the back of the LCD

Running at its native 3840×2400 resolution shows how fine its dot-pitch is,
though I am now running it at 2x:

3840×2400

1920×1200 @ 2x

Using the
MonitorControl
utility, I could change the LCD backlight level from software, and the eDP board
automatically powers off the LCD when the Mac Mini tells it to sleep, unlike the
DockLite.

MonitorControl

iMac Neck
Once the new LCD was working over USB-C, I ran into the problem of having to get
the new cable run inside of the iMac’s articulating neck.
The cables connecting to the original LCD are run inside the neck assembly
during manufacturing and then connectors are added afterward since they are too
large to fit through the small openings at the top and bottom of the neck.
Unfortunately this meant I had to cut these original cables to get them out, and
it also made it difficult to run a USB-C cable through it.

The smallest diameter of the neck hinge is about 9mm where it meets the dome,
but most USB-C/Thunderbolt cables I tried had at least a width of about 12mm.
Even after trimming off the rubber/silicone of some of them, they often had a
PCB or other stuff inside that was wider than the connector.

Open iMac neck with original cables

Smallest opening at the neck base

The 9mm opening is on a flange that slides inside the base of the neck and is
where the dome attaches to the neck with 5 screws.
It tapers to a smaller opening at the top because there is usually a sleeve that
goes around it to make rotating smoother, though it’s not really needed in my
experience.
I figured I could make a new piece like it and make it not taper, allowing the
inner wall to be thinner and its opening wider, ultimately allowing the USB-C
cable to pass through it.

I took some measurements and
modeled
the flange in Tinkercad, then did a bunch of 3D prints making tiny adjustments
each time.
I suppose I’m more of a “measure once, cut 14 times” person.

3D-printed prototypes

Final prototype

Although it’s not load bearing (it is sandwiched between the steel openings at
the top of the dome and bottom of the neck assembly), I wanted the new flange to
be made out of something stronger than my 3D printer could produce.
Once my prototyping was done, I sent the design off to
JLCCNC
to get it machined out of 6061 aluminum.
Their engineer said the thin wall of the vertical tube had to be thicker to get
safely machined, so although the opening ended up not being as wide as I
wanted, it still allowed a USB-C cable to pass through.

It took a few weeks to machine since I was doing this during Chinese New Year.
Although I didn’t like the bead-blasted finish which immediately scuffed up, it
fit perfectly and the dome could securely attach to the neck.

My final design in Tinkercad

Machined flange vs. original

Larger inner wall on my flange

Once I trimmed off some excess rubber from the end of a Thunderbolt cable, I was
able to route it through the opening in the rear of the screen housing, down the
neck, through the new flange, and into the dome.
I then added some shrink tubing to the connector to replace the removed rubber.

Into the screen housing…

down the neck…

through the flange…

to grandmother’s house we go

It was important to keep a bit of slack in the cable through the neck to make
sure its articulation still worked.

Screen upright

Screen extended

Mac Mini Mouting
Once the top was all put back together, I could now focus on mounting the Mac
Mini inside the dome.

I modeled a new circular piece to replace the Juicy Crumb DockLite board and
then added a cross piece to secure the Mac Mini.
I was limited by my 3D-printer’s build plate dimensions so I had to chop off the
bottom of the circle, but there were no mounting holes in that area anyway.
I 3D-printed it, inserted heatserts into the cross piece, and bolted down the
Mac Mini:

Mac Mini mount (with heatserts)

Mac Mini mounted

While every tech reviewer complained about the M4 Mac Mini’s power button being
moved to the bottom, it was actually beneficial to me when putting it inside the
iMac. Underneath the iMac is a removable panel that originally gave access to
the upgradeable RAM and AirPort slots, but I no longer need it.

By mounting the Mac Mini rotated a bit, the power button is now accessible from
the bottom of the iMac and can be pressed just by tilting up the left side of
the iMac a bit.
Since I would only need to press this button on rare occasions, I figured this
would be easier than having to disassemble the Mac Mini to solder an external
power button to it.

Mac Mini power button

I didn’t want to have to open the iMac to reach certain ports, so I bought some
short extension cables for the IEC C7/C8 power port, ethernet, and one
Thunderbolt port.
For now they are just slightly hanging out the back but I’d like to 3D print
some sort of bracket to hold them all in place just behind the port openings and
fill in the voids.

Pigtail cables

Remaining Issues
Aside from having to make the rear port bracket, I thought it also might be neat
to make use of the flip-down optical drive door to put some USB ports behind it.

The eDP LCD controller currently has an annoying “feature” where once the
display goes to sleep, it shows a blue screen with “No Signal” shown for about
10 seconds before completely shutting off.

Update: I received a
new firmware file
from the vendor and was able to flash it with
their programming board
over HDMI.
The blue screen with “No Signal” is now gone and the display immediately goes to
sleep when instructed.

Reflashing the firmware on the eDP controller

If you’re purchasing an eDP controller board, I would recommend just asking the
vendor to disable that functionality when flashing the board.

My iMac G4(K) next to my Mac Plus