Intel-based iMac as a computer and a 2K/5K display

[kvic]

I've known people can convert iMac into a pure monitor for a long long time. Ever since I've been pondering from time to time if it's possible to modify iMac in a way that it can function as a computer and a monitor with a little switch. I didn't give it some serious thought until I recently bumped into this gent's adventure: https://www.tonymacx86.com/threads/...-2006-into-a-monitor-still-a-computer.299258/. That post drew little attention and hence we don't have much information other than what's described in text there.

That was an inspiring piece of work. I dug up some iFixIt's teardown's and available after-market LCD driver kits and gave some thought on a possible design. The following block diagram illustrates my approach:

The internal LCD panel can be used by both iMac and another computer at different time. We could use the OSD button panel to switch the source. Or we could write a piece of software to switch by a mouse click (and eliminating the need of the OSD button panel).

This approach eliminates the need of the after-market inverter board or the need of relatively high power supply to feed such a function. Hence, the after-market LCD driver board could be housed inside the iMac with relatively low power requirement sourced internally.

Challenges in descending order of uncertainty:

• will the iMac's inverter board/LCD power supply continue to work once eDP connector is disconnected from the LCD panel
• internal case space to house the after-market driver board
• space to re-route the mini DisplayPort of the iMac from outside to inside and connect to the after-market board
• space to pass the DisplayPort/HDMI cable from other Mac/PC to inside the iMac
• enough power juice from the iMac's PSU to supply the after-market driver board (less its inverter function) and the iMac's computer function simultaneously

Has anyone attempted such a modification before with success or running into technical roadblocks on a model from iMac 2011 up to iMac 2020? Or someone see issues with such an approach?

NB: In the block diagram. "D" can also be USB-C. So "D - Thunderbolt/mini DP ports/USB-C"

 

[Nguyen Duc Hieu]

Your idea will require:

1. Money for parts (80$ for 2k, 250$ for 5k LCD driver board, plus other things)
2. Knowlegde and skill in electric field for rewiring.
3. Chances are holes must be opened from the backside of the machine => losing aesthetic appearance
4. Labour for such modification.
5. Losing value due to modifications when reselling the iMac.

The cost would simply excess the price of a new 4k monitor. So a major of people will go with external monitor solution.

If you can obtain an old 27" 2k iMac for free, converting it to a stand-alone LCD, and/or stuffing the logicboard of an Mac Mini M1 inside it may look cool enough.

 

[kvic]

5K LCD driver board is already available below $200 price point. The price will continue to drop when demand goes up. Same goes with the resale value of iMac (the oldest 5K iMac is already 7yo) when Apple accelerates the transition away from Intel.

These iMac's as monitor simply look great in quality and aesthetically (thanks to the chin). I have little idea why so many people complain about the chin in the M1 iMac. Without it, aesthetically the aspect ratio of the whole product will look worse IMO, just like most 4K and 5K monitors in the PC market.

PC monitors may come with same good quality panel but the casing is usually poorly designed or may even occupy a larger volume than an iMac. So if we could keep the computer functional and additionally accept external display inputs, the end product is amazing. It gives people a sense of fullness and completeness inside out (instead of emptiness in a gutted iMac into monitor conversion). People may or may be using the computer function as daily driver. But it could serve many purposes at low power consumption. The bare availability and easy accessibility to the computer function when needed inside the same volume of a monitor is just beautiful. Not to mention for urban dwellers, desk real estate is at premium.

If holes need to be punctured to pass cables, I've got some ideas to make it aesthetically look good. But I think to begin with we simply use the memory access door. The number one uncertainty IMO: will the iMac's inverter board continue to function after the LCD panel is disconnected from the Logic Board?

Now thinking a bit more I should also added picture quality. People who gutted their iMac into monitor seldom discussed picture quality. Do the colours look as good and accurate as driven by Apple's Logic Board?

 

[Nguyen Duc Hieu]

Now thinking a bit more I should also added picture quality. People who gutted their iMac into monitor seldom discussed picture quality. Do the colours look as good and accurate as driven by Apple's Logic Board?

Picture quality is not an issue, if you know how to calibrate.
The controller chip on the 5K LCD driver board tends to run very hot, you will need a good design for effective ventilation.
Thereotially and technically, yes, you can modify an iMac to function as both monitor and AIO computer.
The remaining issues are:
1. Are you skilled enough to do it? (How)
2. Does it worth your effort? (Why)

 

[kvic]

I'm aware of macOS color profile for calibrating colors. That's okay for fine tuning, isn't it? Assuming the after-market LCD driver board isn't terribly bad. I don't see any tunables on those driver boards other than the usual color adjustment options through OSD. But I meant monitors ranging from dirt cheap to premium price come with similar options inside OSD..

It seems you missed one essential point in my 'design' described in post #1. I'm re-using the inverter board from the iMac for various reasons. One of them is exactly reducing power consumption on the after-market driver board. I don't expect 5K board runs hotter because it's '5K'. LCD panels inside older iMac is 'terribly' power inefficient by today's standard. I expect those '2K' after-market boards run as hot as the '5K' boards in stock config that sellers intend buyers to run. So in my 'design' I won't use the high power function on the driver board, that leaves me, say a 5K board, with a power consumption slightly more than half of the Apple M1 processor. I won't imagine that'll be very hot but good cooling is still desirable.

Do note that above is based on analytical thinking not first-hand experience. Hence, why this thread. With all components available, I probably could do a proof-of-concept experiment in less than 1 hour. There isn't much to do to prove it work or not. However, with all the hassle of ordering, waiting, and taking apart an iMac, then in much less than 1 hr, one finds out it won't work. That's terrible and I want to avoid as much as possible..

 

[Nguyen Duc Hieu]

I'm aware of macOS color profile for calibrating colors. That's okay for fine tuning, isn't it? Assuming the after-market LCD driver board isn't terribly bad. I don't see any tunables on those driver boards other than the usual color adjustment options through OSD. But I meant monitors ranging from dirt cheap to premium price come with similar options inside OSD..

It seems you missed one essential point in my 'design' described in post #1. I'm re-using the inverter board from the iMac for various reasons. One of them is exactly reducing power consumption on the after-market driver board. I don't expect 5K board runs hotter because it's '5K'. LCD panels inside older iMac is 'terribly' power inefficient by today's standard. I expect those '2K' after-market boards run as hot as the '5K' boards in stock config that sellers intend buyers to run. So in my 'design' I won't use the high power function on the driver board, that leaves me, say a 5K board, with a power consumption slightly more than half of the Apple M1 processor. I won't imagine that'll be very hot but good cooling is still desirable.

Do note that above is based on analytical thinking not first-hand experience. Hence, why this thread. With all components available, I probably could do a proof-of-concept experiment in less than 1 hour. There isn't much to do to prove it work or not. However, with all the hassle of ordering, waiting, and taking apart an iMac, then in much less than 1 hr, one finds out it won't work. That's terrible and I want to avoid as much as possible..

For AIO machines like the iMac, you have only 1 calibration control panel (OS side). That said, if you are happy with its color, then the LCD are well calibrated out of box.
For separate LCDs, you have 2 calibration control panel. Depends on the integrated OSD software embedded in the board, calibration ranging from simple to complicated. But as the LCD is already good, it won't impact the color quality (i.e you might get the color you want, after calibration)

The on sales 2k/5k LCD driver board, when successfully connected, will turn the LCD to a stand-a-lone monitor, you will need to connect it via the external DP/TB port of the iMac, then re-route the cable back inside. The other PC/Mac shall use another port on the LCD driver board. This design will let the eDP port on the logic board un-connected/unused.

If you intend to use the eDP port on the logic-board as well, you will need to add another piece of part: a 2 to 1 LVDS selector which can handle eDP signal. I think this kind of board is rare and expensive, as monitors are not commonly designed this way.

5K LCD driver board is definitely hotter than 2k LCD driver board. Take a look at their pictures, the 5K board has a fan and heat sink, while the 2k does not.

 

[kvic]

If you intend to use the eDP port on the logic-board as well, you will need to add another piece of part: a 2 to 1 LVDS selector which can handle eDP signal. I think this kind of board is rare and expensive, as monitors are not commonly designed this way.

This is interesting. I don't know such a device exists. I would think the switch is not programmatically controllable (?). Then you have to extend the physical switch in some way to make it easily accessible from outside. More on this device below.

My original plan is not to use the eDP output from Logic Board (as you could see in the illustration in #1). Here is my crux of uncertainly that I'm afraid I've to repeat for the third time. With the condition that the Logic Board's eDP won't be connected to the LCD panel, will the iMac's inverter board/backlight circuity continue to operate? If it won't, it's a show stopper as re-using the inverter/backlight circuity is a big part in my plan.

5K LCD driver board is definitely hotter than 2k LCD driver board. Take a look at their pictures, the 5K board has a fan and heat sink, while the 2k does not.

I see bigger heatsinks for sure. I haven't seen fans from those sellers' ad. Yesterday I bumped into "making your own 5K monitor" thread on this forum (what a rare species on MR). I saw some people did add a fan to the heatsink.

I'm afraid my plan will potentially run into a couple of technical roadblocks for 5K. The number of DisplayPort inputs is limited on 5K driver boards. USB-C input is very limited if ever exists. Also only 2017 27-inch 5K iMac (and newer) supports 5K external monitors. Earlier models are out of luck.

Here comes the magic of "eDP splitter" (?) device you said earlier. I think for 5K one possible approach is to use of such a device so that not to route the output to external display back to the 5k driver board. Cost alone probably makes a 5K project not worth pursuing in 2021.

What a journey of thought experiment.

 

[Nguyen Duc Hieu]

My original plan is not to use the eDP output from Logic Board (as you could see in the illustration in #1). Here is my crux of uncertainly that I'm afraid I've to repeat for the third time. With the condition that the Logic Board's eDP won't be connected to the LCD panel, will the iMac's inverter board/backlight circuity continue to operate? If it won't, it's a show stopper as re-using the inverter/backlight circuity is a big part in my plan.

What a journey of thought experiment.

If you don't insist on re-using the eDP port on iMac logic board, it'll be much easier to do, and others have successfully done that already.
You'll need to disconnect the backlight board from the logicboard completely, and reroute the control signal to the LCD driverboard (the how-to will vary depending on LCD models).
LCD driver board can be purchased as one set, which include everything you need to convert the LCD panel of the iMac to a monitor. (Driverboard, Backlight board, signal cables, 5 buttons OSD control keyboard ), you can rewire the iMac PSU to power the driverboard, or use a laptop powerbrick (19V or something).

 

[kvic]

no, nO, NO. I never intend to do a monitor only conversion or build my own 5K monitor.

I also cannot accept a half-baked solution by gluing a LCD driver board + a 'headless' iMac together.

Re-using the iMac's backlight board (or inverter board as I called it in previous posts) is a key part in my plan. Without it, it's a show stopper for me.

The after-market LCD driver board and the iMac should be integrated together as seamless as possible. On the outside, minimal damage to its look, and functionalities. On the inside, circuitry re-use as much as possible to preserve its elegancy.

If not achievable, I've to dream up something else or consider a different path. 4K monitors are possible options but knowing they don't work optimally with Mac's holds me back. Hopefully 4.5K, 5K and 6K monitors will become trendy in the market place.

 

[Nguyen Duc Hieu]

no, nO, NO. I never intend to do a monitor only conversion or build my own 5K monitor.

I also cannot accept a half-baked solution by gluing a LCD driver board + a 'headless' iMac together.

Re-using the iMac's backlight board (or inverter board as I called it in previous posts) is a key part in my plan. Without it, it's a show stopper for me.

The after-market LCD driver board and the iMac should be integrated together as seamless as possible. On the outside, minimal damage to its look, and functionalities. On the inside, circuitry re-use as much as possible to preserve its elegancy.

If not achievable, I've to dream up something else or consider a different path. 4K monitors are possible options but knowing they don't work optimally with Mac's holds me back. Hopefully 4.5K, 5K and 6K monitors will become trendy in the market place.

The Youtube video is just a reference for your project. It provides a lot of details to learn from, including tools, parts, where to buy from, etc.
Base on that, you'll have to work it out with a thorough plan, depending on the type of LCD panel your have, and options you choose.
The thick bezel of 2009~2011 iMacs will be easier to work with, the thin bezel iMac is more difficult.
to mod the thin bezel iMacs, you might need to remove the internal speakers go free some spaces. They are mediocre anyway, nothing to miss, except for the booting chime.
Or if you still want the booting chime, just cut off the excessive plastic resonant chamber. They would sound a little different, but you'll have the booting chime.

 

[kvic]

After some digging, to answer my top concern

Re-using iMac's inverter board as in post #1 should work (but not as ideal as I would want it to be).

Seems the backlight level control signals are embedded in the eDP connector. Once disconnected, the LCD panel won't receive it from the iMac but instead from the aftermarket LCD driver board. The level signals and actual backlight driving signals are separate. Hence, mix & match in my design should theoretically work.

One piece of evidence is the following block diagram. It's a LCD timing controller chip. A very similar chip is used in 5K iMac LCD panels:

With some non-trivial hacking, we may be able to wire the level control signals from iMac to the LCD panel. Hence, control the brightness by software from within MacOS. The potential down side is not sure what OSD controls we might lose from the LCD driver board. Perhaps some perhaps none.

Bonus finding

In 2011 27-inch iMac, the backlight driver board/LCD inverter board is a separate daughter board sitting next to the PSU board. Unlike the 'giant' heavy PSU board, the LCD inverter board is half the size but sitting on vibration-damping double rubber o-rings on all four screws.

Thin models since 2013, the inverter board is integrated on the Logic Board. As far as I could see, there is no special vibration damping mechanism. Perhaps it takes one to disassemble it to notice such small details.

Why is it worth mentioning? Because I saw this thread earlier on: https://forums.macrumors.com/thread...ing-noise-with-low-display-brightness.2298812

edit: corrected year and made it clear thin models

 

[kvic]

[deleted original double post; now re-used for responding post #13]

If you wants to keep the iMacs functioning 100% (internal LCD), the input switching circuit is unavoidable. This works the sames as on TV, when you can switch signals between the TV turner, TV internal CPU (smart TV function), and external input source. In the old time, when TVs weren't smart, the T-con board has 2 LVDS input, 1 for TV tuner board, 1 for external source.
Thereotically, it would be the same mechanism in this case: Intercept the signal between iMac's logic board and LCD panel control board (the eDP cable) and insert a eDP/LVDS switching circuit there.
Position 1: LCD panel receives input signal from external source (via the driver board), the iMac still see a dummy LCD.
Position 2: LCD panel receives input signal from iMac logicboard and cut of connection from the driver board.
Switching can be done mechanically on the driver board control keys.

You can send your request to the LCD driverboard maker to add such a switch.

@Nguyen Duc Hieu Seems you still haven't realized I'm already using off-the-shelf aftermarket driver board for the 'switching' purpose.

An improved version to my original proposal is converting iMac's eDP connector to a regular DisplayPort connector. I believe it's do-able by dedicated tinkerers with little cost. The benefit is not required to re-route the iMac's display output from outside into inside.

It's possible to create tailor-make boards. Who knows if ambitious sellers from China are already monitoring this thread..

 

[Nguyen Duc Hieu]

If you wants to keep the iMacs functioning 100% (internal LCD), the input switching circuit is unavoidable. This works the sames as on TV, when you can switch signals between the TV turner, TV internal CPU (smart TV function), and external input source. In the old time, when TVs weren't smart, the T-con board has 2 LVDS input, 1 for TV tuner board, 1 for external source.
Thereotically, it would be the same mechanism in this case: Intercept the signal between iMac's logic board and LCD panel control board (the eDP cable) and insert a eDP/LVDS switching circuit there.
Position 1: LCD panel receives input signal from external source (via the driver board), the iMac still see a dummy LCD.
Position 2: LCD panel receives input signal from iMac logicboard and cut of connection from the driver board.
Switching can be done mechanically on the driver board control keys.

You can send your request to the LCD driverboard maker to add such a switch.

 

[kvic]

An improved version to my original proposal is converting iMac's eDP connector to a regular DisplayPort connector. I believe it's do-able by dedicated tinkerers with little cost. The benefit is not required to re-route the iMac's display output from outside into inside.

Turns out such cables already are off-the-shelf parts! I found most vendors from China and one from America:

If my manual counts based on TechRepublic/iFixIt teardown photos are correct:

• 27-inch 2011 iMac: eDP connector = 30 pins
• 27-inch 2012/13 iMac: eDP connector = 40 pins
• 27-inch 2014+ 5K iMac: eDP connector = 60 pins

One small detail I didn't notice before. The connector from PSU to LED inverter/backlight board in 2011 model is 6 pins. Two of those pins are coming from the Logic Board! See zoom in pic below and original is here. Turns out one pin should be PWM signal for adjusting the brightness of backlight. The other pin is backlight enable/disable. 2012+ models should be similar though the wirings are integrated into the Logic Board.

Now this makes much more sense to me and also poses new uncertainty. To re-use the LED inverter/backlight board and control backlight natively by MacOS, does it require:

• some kind of presence check of the eDP connection on the Logic Board? and/or
• additional signal paths through the eDP connector between the Logic Board and the LCD panel?

Before my train of thought moves to an alternative direction, let me revise my design a bit:

EDIT: fixed block diagram

 

[kvic]

Goodness me. The devil is in the detail, right?

I've been looking at built-in LED/backlight driver boards from 2011 27-inch as I believe it's the last model with wirings better exposed than later models. I can't believe it. The 2011 27-inch was only manufactured for about one year but there are at least three variations of the the LED/backlight driver boards.

• V1 (variant 1) 4-pin socket/2-pin wiring for the 'vsync/temperature sensor cable'
  
  
  
  
  source: here
• V1 (variant 2) 4-pin socket/2-pin wiring for the 'vsync/temperature sensor cable'
  
  
  
  
  source: here
• V2 (variant 3) 8-pin socket/2-pin (??) wiring for the 'vsync/temperature sensor cable'
  
  
  
  
  source: here

Variant 1 looks like re-use of left-over parts from 2009/2010 27-inch models in the launch batches of 2011 27-inch models. But only two wires in the actual cable rather than four wires (as in 2009/2010). That's very interesting. It implies when the external source input transitioned to Thunderbolt plugs. Brightness control moves completely to 'host software' based.

Variant 2 seems 2009/10-derivative design tailored for 2011 27-inch models. Note that the cable is also two wires only. If the silk print on variant 1 indicative of pin functions: 1 wire for vsync; 1 wire for 'backlight on'.

Apple calls the cable 'vsync/temp sensor cable' but it actually doesn't carry temperature readings! Where did the temp sensor wiring go? Very likely Apple have re-purposed two unused pins from the 30-pin eDP connector. Watch out!

Variant 3 is interesting too. Looks like a design overhaul to break apart from the past. Not sure how many wires in the cable. I bet it's still two. Also not sure if this variant is actually the best for 2011 27-inch models. There could only be two reasons for the overhaul: cheaper to manufacture and/or same or better performance.

 

[kvic]

In the past week or two, I've been asking myself what the f**k is this LCD connectivity all about because looking at my designs/proposals, I felt like I could even get rid of the stupid and clunky aftermarket LCD driver board. I came across simple (or cheaply made?) general-purpose parts (by vendors from China) for LCD display. Those were the first instances reinforcing my belief. Ever since I've been drilling down the rabbit hole..

Fast forward to now, I've just completed my first draft of a schematics for building a prototype based on off-the-shelf parts. Allow me to indulge myself a bit by calling it 'iMakvic Display'. Functionally it will

• easily switch iMac's LCD screen as an internal display and as an external display for another Mac/PC/consoles
• allow iMac to continue function as a 'headless' computer simultaneously while acting as an external display
• continue to monitor temperature inside the LCD screen
• be able to adjust display brightness by MacOS both automatically or manually

I'm going to build a 2K prototype in the coming months. I may destroy my iMac or have a successful prototype. If the latter, I'll update this thread.

Meanwhile, having a much better idea about the LCD mess. Google hears me and returns better results. I stumbled on this blog post yesterday by a very enthusiastic perfectionist (probably right out of college 8 yrs ago?). It's not for iMac but the fundamental principles are similar. Hope it inspires someone who land on this thread in future:

source: here

BTW, does anyone have the datasheet for the 5K LCD panel, namely LM270QQ1, LM270QQ2 or their variants? Ping me. I could offer you a discount on my 2K prototype (lol..well if proven successful).

 

[Analog Kid]

While I keep hoping Apple brings back target display mode, I don't have much hope. I'm guessing that Airplay to Mac is meant to replace it, but I understand Airplay to Mac sends compressed display content so probably isn't suitable for using the 5k display at full resolution.

Given all of that, what's happening in this thread has my interest. I've added it to my watch list.

 

[kvic]

Progress update

Contacted a few 'factories' in China and tried to get my custom cabling made. No dice. Minimum order is beyond reasonable for a first prototype. So was forced to go down the route of assembling from parts not really meant to glue together. Too many wires to handle comfortably tbh. Made multiple mistakes on draft drawings. Then again on soldering. Anyway, after polishing my micro soldering skill for a week or two, here we go.

Will face the moment of truth in the coming weeks if it functionally works or not

 

[Mars911]

please update

 

[kvic]

Initial trial unfortunately failed (but didn't result in any damage either). iMac couldn't detect the presence of the internal LCD and refused to boot. This could be caused by poor soldering joints and/or not understanding how Apple's connector works. Due to lack of equipment, it's challenging to debug the issue. At the moment the project has been low on my priority list, I hope to revive it in future.

Interestingly Wendell from Level 1 Tech did a video on DisplayPort in the past few days. He mentioned Apple's unusual way of DP usage. Seems he might have seen something funny on Mac's.

 

[Mars911]

Sorry to hear about it.

 

[4nthony]

I've known people can convert iMac into a pure monitor for a long long time.

I have a 2017 iMac 18,3 which has some logic board issues and I would love to find a way to remove the computer guts and convert it into a full-time display.

Do you have a source for doing this to a 2017 iMac?

I haven't found the right mix of search terms and I keep getting articles that either mention Target Disk Mode or the iMac in the article is 2014 and older.

Thanks!

 

[Nguyen Duc Hieu]

I have a 2017 iMac 18,3 which has some logic board issues and I would love to find a way to remove the computer guts and convert it into a full-time display.

Do you have a source for doing this to a 2017 iMac?

I haven't found the right mix of search terms and I keep getting articles that either mention Target Disk Mode or the iMac in the article is 2014 and older.

Thanks!

Can you take a picture of the model label on your LCD panel?

I'll send you the link of the LCD driver board.

 

[4nthony]

Can you take a picture of the model label on your LCD panel?

I'll send you the link of the LCD driver board.

I'm not near the iMac at the moment to snap a picture, but I have this in my notes:

Model Identifier: 18,3
Model Number: A1419
EMC: 3070

Thank you!

 

[Nguyen Duc Hieu]

I'm not near the iMac at the moment to snap a picture, but I have this in my notes:

Model Identifier: 18,3
Model Number: A1419
EMC: 3070

Thank you!

This information is not usable.
I need the part number of the LCD panel.
Something like one of the below


LM270QQ1 SDA1 2014
LM270QQ1 SDA2 2015
LM270QQ1 SDB1 2016
LM270QQ1 SDC1 2017
LM270QQ1 SDE1 2019
LM270QQ1 SDF1 2020 (iMac 2020)

DIY 5K Universal R1811 V.4 Driver Board USB-C Freesync EDP DP1.4 Compatible for iMac LM270QQ1 LM270QQ2 Screen External Monitor - AliExpress 7

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