Display brightness of my old iMac

[Monja96]

I am not sure how to thoroughly check the apple inverter, but if you can confirm that the voltages at the plug with the 6 cables are correct then it may be the inverter. Your PWM module shows 13.3 which is correct. I have experimented with various frequencies between 1kHz and 20 kHz and they all worked. With the low frequency the screen starts to show some flicker. Check the cables going to the Apple inverter to make sure each cable goes to the correct pin.

Hi again,
I’ve connected everything and checked it all with the multimeter. Everything seems fine except for one thing: the ENA pin on the inverter is reading 1.61V. I’m not sure why—it’s supposed to be 3.3V.
When i check the logic board , the wire is 3.3v. maybe is the inverter?

 

[Monja96]

This is my diagram—the same one that @iMacConversionEnthusiast made

Apple Inverter
PIN 1 (Ena)	LV2 (Level Converter
PIN 2	12v Chinese Board
PIN 3 (pwm)	PWM OUT
PIN 4	GND Chinese Board
PIN 5	12V Chinese Board
PIN 6	GND Chinese Board

Chinese Board
12v	PIN 2
12v	PIN 5
BLO	HV2 Level Converter
GND	PIN 4
GND	PIN 6

On the other hand... I should just need to connect this cable to the inverter, there’s no other connection required—aside from connecting the Chinese board to the screen through the golden pin, etc.


At this point, I don’t even know where the problem is anymore.

Level Converter
GND	GND 5V Step Down
HV	5V Step Down
HV2	BLO Chinese board
GND	GND 3.3V Step Down
LV	3.3V Step Down
LV1	PIN 1 ENA Apple Inverter

 

[SubDriver]

All - I finally had the time to put the finishing touches on my conversion. I decided to not connect the SD card reader in the end since I have multiple other card reader options should I need one. Other than that, it is complete. I have attached a more or less final document (.pdf document) detailing the conversion - I may add some pictures to it eventually.

I will soon be shifting my efforts over to converting my 2017 iMac to a standalone 5K monitor. It will be paired with this converted 2011 monitor to be used in a multiple display setup with my recently purchased M4 Max Mac Studio.

 

[SubDriver]

This is my diagram—the same one that @iMacConversionEnthusiast made

Apple Inverter
PIN 1 (Ena)	LV2 (Level Converter
PIN 2	12v Chinese Board
PIN 3 (pwm)	PWM OUT
PIN 4	GND Chinese Board
PIN 5	12V Chinese Board
PIN 6	GND Chinese Board

Chinese Board
12v	PIN 2
12v	PIN 5
BLO	HV2 Level Converter
GND	PIN 4
GND	PIN 6

On the other hand... I should just need to connect this cable to the inverter, there’s no other connection required—aside from connecting the Chinese board to the screen through the golden pin, etc.


At this point, I don’t even know where the problem is anymore.

Level Converter
GND	GND 5V Step Down
HV	5V Step Down
HV2	BLO Chinese board
GND	GND 3.3V Step Down
LV	3.3V Step Down
LV1	PIN 1 ENA Apple Inverter

@Monja96 I recommend reviewing the .pdf document I just uploaded in the previous post. It may help you diagnose what is going wrong with your display.

 

[iMacConversionEnthusias]

This is my diagram—the same one that @iMacConversionEnthusiast made

Apple Inverter
PIN 1 (Ena)	LV2 (Level Converter
PIN 2	12v Chinese Board
PIN 3 (pwm)	PWM OUT
PIN 4	GND Chinese Board
PIN 5	12V Chinese Board
PIN 6	GND Chinese Board

Chinese Board
12v	PIN 2
12v	PIN 5
BLO	HV2 Level Converter
GND	PIN 4
GND	PIN 6

On the other hand... I should just need to connect this cable to the inverter, there’s no other connection required—aside from connecting the Chinese board to the screen through the golden pin, etc.


At this point, I don’t even know where the problem is anymore.

Level Converter
GND	GND 5V Step Down
HV	5V Step Down
HV2	BLO Chinese board
GND	GND 3.3V Step Down
LV	3.3V Step Down
LV1	PIN 1 ENA Apple Inverter

Hi, what's the amps of the power supply you are using? Are you measuring the 1.6V while a source is connected to the HDMI and the Chinese board is on (the green light on the keypad is on)?

 

[iMacConversionEnthusias]

Hi All, what do you think about the following? I went a bit experimenting and applyed the setup for the original inverter to the Chinese inverter. I used a PWM and one step down to 3.3V for it. The ENA voltage I left to 5V. The 12V and GND for the inverter/screen I took directly from the external PSU. The result is not bad - somewhere between the straight Chinese board brightness and the brightness with the imac inverter but with about half the power consumption of ~75-80W, ~ 42W and low heat emission at 100% brightness. I still have two fans but they are small and I supplied them with 9V instead of 12V to reduce RPMs as full RPMs are not needed and of course to reduce the noise. I used the C2 model of the screen which I reported earlier it was yellowish with the full conversion and now it is not yellowish. The temperature inside does not go higher than 35C. It is my wife's external screen and it has been in use for the last week for full day of work with no problems.

 

[Monja96]

Hi, what's the amps of the power supply you are using? Are you measuring the 1.6V while a source is connected to the HDMI and the Chinese board is on (the green light on the keypad is on)?

PSU is 12V 5A. Green light on and HDMI conected

 

[Monja96]

Hi, what's the amps of the power supply you are using? Are you measuring the 1.6V while a source is connected to the HDMI and the Chinese board is on (the green light on the keypad is on)?

The inverter only needs to connect with this , no?

 

[iMacConversionEnthusias]

The inverter only needs to connect with this , no?

Yes, only this as far as I know. But I have not used the inverter model you have.

 

[iMacConversionEnthusias]

PSU is 12V 5A. Green light on and HDMI conected

OK, so what is the result you get. Is it black screen or something else? If it is black screen take a torch and point the light at the screen and check if there is image. If there's image it means your back light is not getting switched on.

 

[SubDriver]

PSU is 12V 5A. Green light on and HDMI conected

You might try to find a more powerful PSU. At full brightness, the iMac screen pulls ~75-80W. This means for a 12Vdc signal, it is demanding between 6-7 amps alone. Your 5A power supply simply may not be powerful enough.

 

[SubDriver]

Hi again,
I’ve connected everything and checked it all with the multimeter. Everything seems fine except for one thing: the ENA pin on the inverter is reading 1.61V. I’m not sure why—it’s supposed to be 3.3V.
When i check the logic board , the wire is 3.3v. maybe is the inverter?

This looks like the same thing that happened to me when I tried using the logic level converter board. I would get 3.3Vdc output from the board, but the inverter pin would not read 3.3Vdc and the screen would remain black. This is why I changed my conversion to use the buck regulator instead. The guide I uploaded in post #303 shows how I connected it. For your situation, using a buck converter would eliminate one of the voltage step down converters and the logic level converter.

 

[Monja96]

This looks like the same thing that happened to me when I tried using the logic level converter board. I would get 3.3Vdc output from the board, but the inverter pin would not read 3.3Vdc and the screen would remain black. This is why I changed my conversion to use the buck converter instead. The guide I uploaded in post #303 shows how I connected it. For your situation, using a buck converter would eliminate one of the voltage step down converters and the logic level converter.

Yes, you're describing exactly what's happening to me—black screen and nothing else. I have your guide, but the problem is that I cut the wires from the Molex 16-pin (PSU to inverter), and now I don't know which ones I need to connect.


Could you guide me and tell me which wire goes where? For example: PSU Pin 2 (Vin) to Inverter Pin 14 (Inverter +).


Also, I don’t understand what you mean by "buck converter."

 

[Monja96]

This looks like the same thing that happened to me when I tried using the logic level converter board. I would get 3.3Vdc output from the board, but the inverter pin would not read 3.3Vdc and the screen would remain black. This is why I changed my conversion to use the buck converter instead. The guide I uploaded in post #303 shows how I connected it. For your situation, using a buck converter would eliminate one of the voltage step down converters and the logic level converter.

I have followed your guide, but since I have the buck converter, I used the other step-down converter as shown in your February guide. I have achieved 3.3 volts at the ENA pin, but the screen remains black.


Is this normal? Do I still need the buck converter?


I can't measure the frequency; my multimeter doesn't display Hz, but the voltage is correct, and my PWM setup is 13.3 at 100%.

Do I absolutely need the buck converter from the brand you mentioned? Shipping costs to my country are exorbitant. What alternatives do I have? AliExpress?

 

[SubDriver]

Yes, you're describing exactly what's happening to me—black screen and nothing else. I have your guide, but the problem is that I cut the wires from the Molex 16-pin (PSU to inverter), and now I don't know which ones I need to connect.


Could you guide me and tell me which wire goes where? For example: PSU Pin 2 (Vin) to Inverter Pin 14 (Inverter +).


Also, I don’t understand what you mean by "buck converter."

Here is the Buck regulator - it will replace both the voltage step down converter and the logic level converter and should solve the voltage issue to the ENA pin while still providing sleep funcitonality for the screen. I recommend buying this and using it.

I also recommend getting a power supply that is at least 8A to 10A. Your 5A power supply may struggle to drive your screen at a suitable brightness level.

For the wiring:

• the two 12Vdc lines from the driver board need to be connected to pin 2 and pin 5 on the inverter
• the two GND lines from the driver board need to be connected to pin 4 and pin 6 on the inverter
• the 3.3Vdc BLO line coming from the buck regulator board needs to be connected to pin 1 on the inverter
• the PWM line coming from the the PWM board needs to be connected to pin 3 on the inverter

I modified the drawing you posted a couple of months ago to show use of the buck regulator - see below.

 

[SubDriver]

I have followed your guide, but since I have the buck converter, I used the other step-down converter as shown in your February guide. I have achieved 3.3 volts at the ENA pin, but the screen remains black.


Is this normal? Do I still need the buck converter?


I can't measure the frequency; my multimeter doesn't display Hz, but the voltage is correct, and my PWM setup is 13.3 at 100%.

Do I absolutely need the buck converter from the brand you mentioned? Shipping costs to my country are exorbitant. What alternatives do I have? AliExpress?

Here are some AliExpress options for a buck regulator that would probably work (these are from the US site - make sure you shift to the correct site for your country if it doesn't automatically do that). There may be others too.
Option 1
Option 2

 

[Monja96]

Here is the Buck regulator - it will replace both the voltage step down converter and the logic level converter and should solve the voltage issue to the ENA pin while still providing sleep funcitonality for the screen. I recommend buying this and using it.

I also recommend getting a power supply that is at least 8A to 10A. Your 5A power supply may struggle to drive your screen at a suitable brightness level.

For the wiring:

• the two 12Vdc lines from the driver board need to be connected to pin 2 and pin 5 on the inverter
• the two GND lines from the driver board need to be connected to pin 4 and pin 6 on the inverter
• the 3.3Vdc BLO line coming from the buck regulator board needs to be connected to pin 1 on the inverter
• the PWM line coming from the the PWM board needs to be connected to pin 3 on the inverter

I modified the drawing you posted a couple of months ago to show use of the buck regulator - see below.

View attachment 2501818

Wooooo , Thanks a lot.

I’ve tested your old schematic and attached an image showing how I made the connections.


I still don’t have the buck converter you recommended, so I used the logic board converter I had.
Should I be seeing anything?
I’m starting to think the inverter might be broken…
Do you recommend buying the same inverter again or the other version that seems to have fewer issues?

 

[iMacConversionEnthusias]

Deleted.

 

[Monja96]

Deleted.

Why?

 

[SubDriver]

Wooooo , Thanks a lot.

I’ve tested your old schematic and attached an image showing how I made the connections.


I still don’t have the buck converter you recommended, so I used the logic board converter I had.
Should I be seeing anything?
I’m starting to think the inverter might be broken…
Do you recommend buying the same inverter again or the other version that seems to have fewer issues?

I would first get a more powerful power supply. One that delivers 8-10 amps.

I think you reversed the HV and LV sides for the logic level converter in the diagram. The 5V and BLO signal should go to the HV side and the 3.3V and ENA lines should be on the LV side

 

[iMacConversionEnthusias]

Why?

Hi, because looking in more detail at your drawing I realised that the capital letters HV and LV on the drawing are reversed but actually you have made the connections correctly. SubDiver pointed out in his post the same thing. So follow the text in his message and ignore the word "reversed".

 

[Monja96]

I would first get a more powerful power supply. One that delivers 8-10 amps.

I think you reversed the HV and LV sides for the logic level converter in the diagram. The 5V and BLO signal should go to the HV side and the 3.3V and ENA lines should be on the LV side

But im using the original PSU. wouldn't that solve the problem?

 

[SubDriver]

But im using the original PSU. wouldn't that solve the problem?

Yes. I guess I missed that you are using the original PSU. Sorry about that. I didn’t look at that in your diagram but I see it now.

I thought I might have a bad inverter back when I was using the logic level converter and had the same symptoms you are having.

You can test out your inverter by simply removing the logic level converter and the BLO line from the signal path. Connect a 3.3Vdc line directly from one of your step down converters to the ENA pin on the inverter.

Doing the above will turn on the backlight anytime the power supply is turned on (i.e., no display sleep functionality), but it is otherwise no harm to the system - just remember to turn off the power supply when you are done.

If the display doesn’t work when connected like I describe above, then it is a fair chance you have a bad inverter (this assumes all other wiring connections are correct, etc.).

 

[Balsie]

Wooooo , Thanks a lot.

I’ve tested your old schematic and attached an image showing how I made the connections.


I still don’t have the buck converter you recommended, so I used the logic board converter I had.
Should I be seeing anything?
I’m starting to think the inverter might be broken…
Do you recommend buying the same inverter again or the other version that seems to have fewer issues?

Hello Monja96, I looked at your connection from the original PSU.
I see on your diagram that PSU_ON is connected to the Chinese board, is that correct?
If so, it will never work.

 

[Monja96]

Hello Monja96, I looked at your connection from the original PSU.
I see on your diagram that PSU_ON is connected to the Chinese board, is that correct?
If so, it will never work.

That's correct, that's how I have it connected. What is the issue?
Thanks!