iMac 27" as Monitor (not Target Display Mode)

[rvbcrs]

Ok, so I have an old iMac 2010 with a dead motherboard. I want to use the display part of the iMac as an external display. I have sourced a LCD controller for driving the display through DVI, HDMI or DP.

This controller also has a driver module for the backlight of the LCD and a power adapter (12V).
I could just put everything in and let the controller board drive the LCD and backlight and just use the power adapter, but I wanted to see if I can use the still perfectly good iMac PSU and the backlight inverter to drive the LCD.

I have the following PSU:

I found that to power on the PSU you have to short PIN6 (PS_ON) with PIN5 or PIN7 (GND). If not the PSU will be in OFF mode and there will be no power on the 12V rails.

Ok, so far so good, but if I short the PS_ON with GND nothing seems to happen, the LCD is not turned on and there seems to be flowing no power to the inverter board!

I found a schematic and pinout of the connector on the motherboard side, but I seem to have the correct pins.

Can anyone (maybe @USB3foriMac) can help me out? I'm not an electrical engineer nor is my main language English so please bear with me

 

[Nguyen Duc Hieu]

When you short out PIN6 (PS_ON) with GND, could you get stable power from the 12V rail?
Anyway, wouldn't it be more value to sell the PSU and use the cheap Power adapter sold together with the LCD driver board?

 

[rvbcrs]

When you short out PIN6 (PS_ON) with GND, could you get stable power from the 12V rail?
Anyway, wouldn't it be more value to sell the PSU and use the cheap Power adapter sold together with the LCD driver board?

On what pins do I need to check? just to be sure?

I could sell the PSU, but the thing is, I would like to get this to work, just for experiment sake and also the original inverter is able to drive the backlight stronger. The LCD driver board is more dim.

 

[Nguyen Duc Hieu]

On what pins do I need to check? just to be sure?

I could sell the PSU, but the thing is, I would like to get this to work, just for experiment sake and also the original inverter is able to drive the backlight stronger. The LCD driver board is more dim.

The original backlight board receive 2 type of signals from the logicboard
1. To turn-on the light. (pin 13 in the schematic)
2. To adjust the brightness. (pin 6 in the schematic)

There is a rather detailed instruction on how to control brightness in this post, it may provide you with some ideas how to apply to your case.

2011 iMac Graphics Card Upgrade

Backlight Control Background: The 2011 iMac display backlight system uses pulse-width-modulation (PWM) to control backlight intensity. A PWM control signal is generated within the logic board-video card circuit and routed to the PWM input on the backlight board. The PWM frequency is 13KHz and...

forums.macrumors.com

After successfully re-use the PSU and backlight board. You may find a way to use the original PSU to feed the LCD driver board your have purchased, and rewire the iMac power button to switch on/off the whole system as well.

 

[rvbcrs]

The original backlight board receive 2 type of signals from the logicboard
1. To turn-on the light. (pin 13 in the schematic)
2. To adjust the brightness. (pin 6 in the schematic)

There is a rather detailed instruction on how to control brightness in this post, it may provide you with some ideas how to apply to your case.

2011 iMac Graphics Card Upgrade

Backlight Control Background: The 2011 iMac display backlight system uses pulse-width-modulation (PWM) to control backlight intensity. A PWM control signal is generated within the logic board-video card circuit and routed to the PWM input on the backlight board. The PWM frequency is 13KHz and...

forums.macrumors.com

After successfully re-use the PSU and backlight board. You may find a way to use the original PSU to feed the LCD driver board your have purchased, and rewire the iMac power button to switch on/off the whole system as well.

Thanks! for your help!!
I was under the assumption that if I would trigger the PS_ON the inverter would also feed the LCD! But I need a bit more electronics if I read correctly!
Ok, so after I short PS_ON with GND I will see if I can measure 12V on the VCC and GND pins of the inverter board. I then need the backlight controller board to set the brightness and trigger the "turn on" signal of the inverter? Correct so far?

I'm already able to use the stanby 12V of the PSU to power the LCD driver board! I indeed want to try to connect the original power button to short PS_ON and GND, or do I need something like this:
6A DC 3 v 3.3 v 3.7 v 5 v Elektronische Schakelaar Klink Bistabiele Self locking Trigger Board voor LED Motor Driver Solar Lithium batterij|electronic board|dc dcboard electronic - AliExpress

 

[Nguyen Duc Hieu]

As the iMac 2010 turns on the LCD backlight several seconds after pushing the power button, I assume that the logicboard send some kind of signal (pulse signal perhaps) to the backlight control board. So when you just simply short a certain pin to ground, it doesn't trigger the power.

 

[Restrox]

Hi, I'm trying to do the same thing and I wanted to know if you were able to solved it?

 

[Nguyen Duc Hieu]

Hi, I'm trying to do the same thing and I wanted to know if you were able to solved it?

If you don't insist on re-using the original Mac PSU, then it would be easy. Just connect the LCD driverboard to the LCD panel, and you have DIYed a 27" 2K monitor.