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Converting an old iMac into a standalone monitor

  • apple
  • repair
  • monitor

This is a fantastic way to upcycle an old iMac that would otherwise be e-waste. I was able to get a 24" 1920x1200 sleek-looking monitor out of this for about $50 in parts.

This blog post feels a bit long but it's just a lot of images and reference material. To skip around, here are some links to the sections:

Most of the images are bigger than they appear in this blog post. Right click and open in a new tab to see the full size.

Figuring out which iMac you have

I'm working with an Apple iMac from 2008, the year before Apple started adding target display mode to iMac's which allows standalone monitor functionality out of the box. In order to figure out which iMac model I have, I used one of the many serial number lookup sites. Here are a couple:

Serial number lookups:

iMac details:

  • Serial No: QP8390/Z0KM
  • Apple Model No: A1225 (EMC 2211)
  • Model ID: iMac8,1
  • Apple Order No: MB325LL/A

LCD details:

  • Resolution: 1920x1200
  • LCD: LM240WU2 SL B3

You can also confirm the details by looking at the sticker on the back of the LCD panel if you want to pre-disassemble the iMac.

Backside of the LCD panel on an iMac showing off a sticker that shows the manufacturer and model number What the inside of the iMac looks like after it's completely disassembled (leaving only he power supply)

Teardown

For a general teardown guide, see this video by Hugh Jeffreys. We basically need to gut everything except the LCD panel and power supply.

Here are some pics of when I did it so I could keep track of screws:

..
Colored screw guide showing how 3 different lengths of screws are used around the bezel of the monitor. The 2 longest screws go in bottom middle with the 2 medium screws flanking that on both sides and the 6 small screws go along the top in the remaining holesShowing off the specific screw used to hold the LCD panel down to the case after the bezel comes off

Connectors on the LCD:

14-pin backlight connector30-pin LVDS connector for the video signal
14-pin backlight connector on the back of the LCD30-pin LVDS connector for the video signal on the back of the LCD

Connectors from the built-in iMac power supply (ADP-250AF B):

14-pin backlight12-pin mobo (MB)
14-pin backlight power cable coming from the iMac power supply. This connector is labeled as CN10112-pin motherboard power cable coming from the iMac power supply. This connector is labeled as CN102.

Pinouts and references

Here are a bunch of references I found while researching this project:

Power supply connector pinouts for the original iMac power supply (Delta ADP-250AF B) (source via MrSoul):

Note: MrSoul indicates that the BL_ON/P_DIM pinout "are reversed on my diagram."

Pinouts for the Delta ADP-250AF B power supply for CN101, CN102, and CN103. CN102 is labeled 1: GND, 2: P_DIM, 3: PS_ON (+3.3v standby), 4: GND (if SATA), 5: +12v standby, 6: GND, 7: GND, 8: BL_ON, 9: +12v, 10: +12v,11: 12v, 12: GND. CN103 is labled  as 1: GND5v and 2: GND5v. CN101 is labeled as 1 - 5: +24v (standby), 6 - 10: GND, 11: P_DIM, 12: BL_ONPinouts for the power supply to motherboard + SATA power cable (593-0879-A) labled as PS, MB, GD, and SATA. PS is labeled as 1: GND=mb1, 2: +12v (standby)=mb8, 3: GND (if SATA)=mb9, 4: PS_ON (+3.3v standby)=mb2, 5: P_DIM=mb10, 6: GND=mb6, 7: GND=mb7, 8: +12v=mb4, 9: +12v=mb5, 10: +12V=SATA13,14,15, 11: BL_ON=mb3, 12: GND=SATA10,11,12. MB is labled as 1: GND=PS1, 2: PS_ON (+3.3v standby)=PS4, 3: BL_ON=PS11, 4: +12v=PS8, 5: +12v=PS9, 6: GND=PS6, 7: GND=PS7, 8: +12v (standby)=PS2, 9: GND (if SATA)=PS3, 10: P_DIM=PS5, 11: +5v=SATA7,8,9, 12: GND5v=SATA4,5,6. GD is labeled as 1: GND5v=X, 2: GND5v=mb12+SATA4,5,6. SATA is labled as 1 - 3: +3.3v=x, 4 - 6: GND5v=mb12, 7 - 9: +5v=mb11, 10 - 12: GND=PS12, 13 - 15: +12v=PS10

"This is the pinout of the Molex 5569 plug from the genuine Apple ADP-250AFB power supply" (source via DocMaker). This matches the CN102/PS pinouts from above as far as I can tell but the orientation is different:

Pinout of the 12-pin molex 5569 plug from the genuine Apple ADP-250AFB power supply is labeled as 1: GND, 2: 12v (standby), 3: GND (if SATA), 4: PS_ON (2.6v standby), 5: BL_ON, 6: GND, 7: GND, 8: 12v, 9: 12v, 10: 12v, 11: P_DIM/ADJ, 12: GND

Thanks for your help, everyone. My dead old 2008 iMac A1225 EMC2211 will have a new life as a simple display.

This is the pinout of the Molex 5569 plug from the genuine Apple ADP-250AFB power supply. Use of the three 12V pin to power the M.NT68676.2A [LCD controller] board. Connect GND to GND, Use the 5.5x2.1 connector instead of 12V and GND of the CN5 plug of the M.NT68676.2A.

Connect BL_ON and P_DIM/ADJ respectively to pin 3 and 4 of the CN5.

-- DocMaker, https://www.ifixit.com/Answers/View/589418/Power+Supply+pin+(voltage,+start+other)#answer701848


Project schematics

A few people have gratiously documented their schematics (wiring diagrams). These are very helpful references to understand how to wire everything up. It's best to just reference all three and pull out what you need.

MrSoul project schematic (source)Bruce Mac (source via iFixit answer)Comitéquartier Ouest (source)
MrSoul project schematicBruce Mac project schematicComitéquartier Ouest project schematic

Setting up a power button

I use a bistable relay to be able to reuse the original iMac push button.

If you replace it with a classic switch (on/off), you don't need the relay, just that it makes contact between GND and PS_ON.

+12V SB is the only track that always outputs 12v, even if the power supply is not activated (but I assume it is not able to offer much amperage), I use it to power the bistable relay.

-- MrSoul, https://www.ifixit.com/Answers/View/589418/Power+Supply+pin+(voltage,+start+other)#comment802578

Bistable relay example https://aliexpress.com/item/4000820341572.html (source)

Or could probably use a latch circuit.

LCD controller boards

There are a few different 3rd-party LCD controller boards to choose from. This is what drives the LCD panel independent of the iMac and is the main piece that allows this project to be possible.

M.NT68676.2A LCD controller board

A lot of people seem to use this one but I ordered the other one below.

Example for sale: https://www.ebay.com/itm/364454394706

M.NT68676.2A LCD controller board with the connectors labeled as CN5: inverter, CN10: IR interface, CN3: power supply, CN11: key interface, CN25: LVDS interface, CN20: speaker

CN5 (6pin: Inverter connector) pinout:

CN5 pinout (6pin: Inverter connector) labeled as 1: 12v, 2: 12v, 3: BLO (back-light on/off control for panel), 4: ADJ (brightness adjustment for panel), 5: GND, 6: GND

Other board with HDMI and DisplayPort

I opted for this controller anticipating that I would want to connect to things that used HDMI and DisplayPort in the future.

Example for sale: https://www.ebay.com/itm/234611483402

LCD controller board with HDMI, DisplayPort, and USB Type-C inputs Zoomed out picture of the LCD controller board with the different cables it comes with LCD controller board fully wired up to a monitor example Close-up of the power supply PCB they are using in their example.

Panel mount connectors

You can get panel mount connectors to extend the outputs from the driver board to a nice panel mount to the iMac case. Here are a couple options depending on how you want to lay things out. I ended up using this first option and having the HDMI port come out the back of the iMac in the deepest spot in the middle through the old air vent (pictured below).

https://www.aliexpress.com/item/3256804506817061.html

Front view of panel mount HDMI connectors Side view of panel mount HDMI connectors with a dust cover

Panel mount female HDMI with a ribbon cable to a male HDMI connector (extension) Panel mount female DisplayPort with a ribbon cable to a male DisplayPort connector (extension)

Building it back up

Luckily, building on the prior art of people doing this before, this project wasn't too hard to figure out. There is a lot of space to mount things inside the iMac case and I was able to re-use a few standoffs and screws from the original iMac.

Inside of the iMac conversion without the LCD panel on Inside of the iMac conversion with the LCD panel connected but propped up to still be able to access the wiring Another angle of inside of the iMac conversion with the LCD panel connected but propped up to still be able to access the wiring Used some connectors for the P_DIM/BL_ON wires Another angle of the connectors and a better view of the bistable relay for the power button Close-up of the LCD driver board

I used a bistable relay so the power supply turns on when the original iMac power button is pressed. Just spliced into the existing connectors after labeling them. Nice clean result.

Close-up of the bistable relay with 12v (standby) and ground connected on one side and PS_ON and ground connected on the other side

I cut a hole for the panel mount HDMI connector in the grill where the fan used to go. Not very pretty but the panel mount connector covers it all up.

Also had to shave down the right-angle HDMI cable sheath so there would be enough clearance behind the panel when it's stacked up with the panel mount HDMI connecter.

Panel mounted HDMI going through the old vent with a right-angle HDMI on the inside shaved down so it fits behind the LCD panel

The little extra PCB that has the LCD controller push buttons and status LED is just tied to the memory access door on the bottom edge of the iMac for somewhat convienent access after everything is put back together. I thought about doing something more elegant on the back of the monitor with some panel mount buttons but that blows up the cost of the project. I haven't had to change any settings since setting it up anyway.

Final result

Using the references above, I was able to get everything up and running and it's now being used as a second monitor for a MacBook Pro 🎉

It doesn't have the best brightness but perhaps that's just how these old monitors perform anyway. I don't have a good frame of reference for how the original iMac worked before I inherited the e-waste.

Old iMac from 2008 converted to be used as a standalone monitor. Hooked up as a secondary monitor to a MacBook Pro