Display brightness of my old iMac

[Balsie]

Take a penny. Leave a penny.

I managed to use the original apple inverter board for full brightness control together with the chinese control board.

In this scenario the chinese inverter which comes with the controll board is not used.

The pins are basically described on both boards.

From the China control board the ADJ goes to PWN and the BL_ON to the BL_ON of the Apple inverter. Furthermore, the 12 V pins and the GND pins are connected to the respective 12 V pins and the GND pins on the Apple inverter.

The brigthness can also be regulated via the menu of the Chinese Controller board. However, the adjustment bar in the menu is now strangely inverted. So that the maximum screen brightness corresponds to 0% at the adjustment bar of the brightness in the menu.

The maximum brightness should be a voltage of 3.25 V. I was also able to measure this with the multimeter.

Everything works for now. Let's see if it stays stable when the screen is on for several hours.

I have used a iMac 2010 with a LG LM270wq1 SDC2 Screen. I orderd the Control Board Version with Display Port and HDMI

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Further I have used a 12V 5 A Power supply.

Hello, I bought a (working) iMac 27 inch 2009 for 50 euro with a beautiful lcd-screen (no spots or something like that).
I intended to use the original PSU and inverter.
I measured the pin-outs and soldered everything together with the Chinese MB.
The Chinese MB works (green led) and measured the power on the psi.
But nothing happened on the screen and I hear a high pitched sound from the inverter.
I hope someone can advise me (excuses for my English, I'm Dutch).
By the way: first I tested the Chinese MB with the Chinese inverter and that works.

 

[davevsxe]

Hello, I bought a (working) iMac 27 inch 2009 for 50 euro with a beautiful lcd-screen (no spots or something like that).
I intended to use the original PSU and inverter.
I measured the pin-outs and soldered everything together with the Chinese MB.
The Chinese MB works (green led) and measured the power on the psi.
But nothing happened on the screen and I hear a high pitched sound from the inverter.
I hope someone can advise me (excuses for my English, I'm Dutch).
By the way: first I tested the Chinese MB with the Chinese inverter and that works.

Hi all,

As described at the time, I used the original Apple inverter board from the iMac2010. However, I powered it by the China board.

I did not use the Apple PSU. As far as I know, an additional signal had to come from the iMac motherboard in order for the Apple PSU to drive the Apple inverter. So you may be missing this signal.. However, I'm not entirely sure about this, since I have not used the original PSU.

I used Wago Clamps to test my wiring. Then you don't have to solder everything directly. It was actually quite simple.

If you want to use the original PSU, try a step-by-step approach and try to drive the Apple inverter with the China board first.

My wiring:

China Inverter	Apple Inverter
12V	12V
12V	12V
ADJ	PWN
BL_ON	BL_On
GND	GND
GND	GND

I will try to make a video / some pictures of my wiring soonish…

 

[Balsie]

Hi all,

As described at the time, I used the original Apple inverter board from the iMac2010. However, I powered it by the China board.

I did not use the Apple PSU. As far as I know, an additional signal had to come from the iMac motherboard in order for the Apple PSU to drive the Apple inverter. So you may be missing this signal.. However, I'm not entirely sure about this, since I have not used the original PSU.

I used Wago Clamps to test my wiring. Then you don't have to solder everything directly. It was actually quite simple.

If you want to use the original PSU, try a step-by-step approach and try to drive the Apple inverter with the China board first.

My wiring:

China Inverter	Apple Inverter
12V	12V
12V	12V
ADJ	PWN
BL_ON	BL_On
GND	GND
GND	GND

I will try to make a video / some pictures of my wiring soonish…

Hi, thanks for you reply.
I've done the way you wrote, but unfortunately no result.
This afternoon I'm going to connect the Chinese inverter again to the Chinese mb.
I only have one question: on CN6 I can switch the jumper between R28-R116-R27-R25.
On the backside of print these R's are representing 10V-12V-5V-3.3V.
Can you you tell me your setting of this jumper?
Thank you in advance, kind regards.

 

[PaulD-UK]

Quote @Balsie: "
"...on CN6 I can switch the jumper between... ...10V-12V-5V-3.3V."

Here is a data sheet translation for setting that jumper:
"Installation notes; 1-1 In the production process, the operation order is to first connect the signal line and the control line, (check whether the screen voltage jump cap is correct, there are 12V/10V/5V/3.3 channels) check that the connection is correct before powering on."

So the jumper determines the output voltage supplied to the screen backlight driver electronics.
Different screens used with these boards in China require different voltages.
Later Macs use the 12v setting, so I expect ithat's the same for 2009-11 era iMac screens?

 

[Balsie]

Quote @Balsie: "
"...on CN6 I can switch the jumper between... ...10V-12V-5V-3.3V."

Here is a data sheet translation for setting that jumper:
"Installation notes; 1-1 In the production process, the operation order is to first connect the signal line and the control line, (check whether the screen voltage jump cap is correct, there are 12V/10V/5V/3.3 channels) check that the connection is correct before powering on."

So the jumper determines the output voltage supplied to the screen backlight driver electronics.
Different screens used with these boards in China require different voltages.
Later Macs use the 12v setting, so I expect ithat's the same for 2009-11 era iMac screens?

I've tried all the jumper-settings without any result, so I've put him back to 12V.
It was a pity, that I could not use the Apple inverter.
Now it's back with the Chinese inverter and that works.
I have to deal with it and I can live with the "less" brightness.
I think there's no other solution, thanks for the support.

 

[Balsie]

I've tried all the jumper-settings without any result, so I've put him back to 12V.
It was a pity, that I could not use the Apple inverter.
Now it's back with the Chinese inverter and that works.
I have to deal with it and I can live with the "less" brightness.
I think there's no other solution, thanks for the support.

I've tried all the jumper-settings without any result, so I've put him back to 12V.
It was a pity, that I could not use the Apple inverter.
Now it's back with the Chinese inverter and that works.

I've tried all the jumper-settings without any result, so I've put him back to 12V.
It was a pity, that I could not use the Apple inverter.
Now it's back with the Chinese inverter and that works.
I have to deal with it and I can live with the "less" brightness.
I think there's no other solution, thanks for the support.

One final question: what are your institutions in the menu (like brightness and backlight)?

 

[Monja96]

Hello everyone, I have a monitor from an iMac A1213 27" with an LM270WQ1 SD E3 display and a Chinese LCD controller board. I want to solve the brightness issue. I’ve seen several solutions on this forum, but I’m not sure which one is the best. I have the original Apple inverter board.

 

[Monja96]

On my iMac 27 from 2011 I tried connecting the Chinese controller to original apple inverter BL_ON to ENA, ADJ to PWM and off course GND and 12v lines but no backlight, I can see image but no light. Even tried to adjust brightness, contrast, backlight nothing changed. Any suggestion?

Im in the same case. Same inverter also. All that i got is a blackscreen. Do you fix It?

 

[seba.m]

Hello everyone, I have a monitor from an iMac A1213 27" with an LM270WQ1 SD E3 display and a Chinese LCD controller board. I want to solve the brightness issue. I’ve seen several solutions on this forum, but I’m not sure which one is the best. I have the original Apple inverter board.

Same here! I'm now writing on this beautiful Thunderbolt display (from my PC via HDMI) but would like to find a solution for the low brightness.. Especially in bright daylight it feels too dim.
I'm currently powering the the LCD board + BT amp (wired to internal speakers) from the original display Power supply 12V outputs.

 

[Nguyen Duc Hieu]

Same here! I'm now writing on this beautiful Thunderbolt display (from my PC via HDMI) but would like to find a solution for the low brightness. Especially in bright daylight it feels too dim.
I'm currently powering the the LCD board + BT amp (wired to internal speakers) from the original display Power supply 12V outputs.

The LCD kit has 2 boards: the main controller board and the LCD backlight power board.
You can replace the LCD backlight power board with the Apple's one, providing that you know how to do the rewiring.
The 12V line and ground can be wired from any 12V DC power source like the original PSU, not necessary going through the controller board.
Others have done it and confirmed that they got better brightness.
There is a risk, though. One DIYer reported that he fried the controller board because he had been trying to get 12V power from the main controller. This overloaded the regulator chip and caused it to blow up, the main controller chip might have been also infected as well.

 

[seba.m]

Thanks. Here are the inputs detailed to the original main board of the display, coming from the PSU.
I just took the 12V and Ground wires to power the LCD board (blue circle), been working ok for weeks.
You're saying I could in addition, also directly power the backlight board (red circle), with the right knowledge..
I don't recall how many wires the backlight board takes? What needs to be passed to it? Guess I could measure it..
I guess the real question is, if the backlight board is capable of producing more brightness, or if it will be overloaded?
Maybe just would need to find someone selling an improved backlight board..

 

[Nguyen Duc Hieu]

Thanks. Here are the inputs detailed to the original main board of the display, coming from the PSU.
I just took the 12V and Ground wires to power the LCD board (blue circle), been working ok for weeks.
You're saying I could in addition, also directly power the backlight board (red circle), with the right knowledge..
I don't recall how many wires the backlight board takes? What needs to be passed to it? Guess I could measure it..
I guess the real question is, if the backlight board is capable of producing more brightness, or if it will be overloaded?
Maybe just would need to find someone selling an improved backlight board..

View attachment 2455987

View attachment 2455989

There is a very detailed guidance on post #52 above...
It's not an unplug- and-plug solution, as the sockets don't match. You will need to cut and rejoin wires.... Re-use also the Apple black plug is advisable. Cut-off half of the 3 color cable in your photo and rewire them to the Apple back plug while using a multi-meter to check conductivity. You need to read the tiny printed label on the pins and match them together.

And please don't use your memory if you can help it.
You can open your iMac and take a photo....

 

[Monja96]

There is a very detailed guidance on post #52 above...
It's not an unplug- and-plug solution, as the sockets don't match. You will need to cut and rejoin wires.... Re-use also the Apple black plug is advisable. Cut-off half of the 3 color cable in your photo and rewire them to the Apple back plug while using a multi-meter to check conductivity. You need to read the tiny printed label on the pins and match them together.

And please don't use your memory if you can help it.
You can open your iMac and take a photo....

Hy nguyen. I see post #52 but my inverter is from 2011 and doesnt have BL_ON . It have ENA Pin. What i need to do?

 

[Nguyen Duc Hieu]

Hy nguyen. I see post #52 but my inverter is from 2011 and doesnt have BL_ON . It have ENA Pin. What i need to do?

ENA = Enable, same meaning with BL_ON.

 

[Monja96]

ENA = Enable, same meaning with BL_ON.

Yeah , but when i conneted the screen dont turn on

 

[Nguyen Duc Hieu]

Yeah , but when i conneted the screen dont turn on

Noted.

 

[csdesign3]

Yeah , but when i conneted the screen dont turn on

try 12v 5Amp or 6Amp like

davevsxe said in a previous post​

 

[csdesign3]

Im in the same case. Same inverter also. All that i got is a blackscreen. Do you fix It?

i will try when i can a new transformer with 12v at 5Amp or 6Amp

 

[SubDriver]

Thanks for the details in the post. I have been trying to also use the original PSU and Inverter from my 2011 27 inch iMac. And my inverter also has the ENA pin instead of the BL-ON.

As of now, I have the following wiring setup to the 6-pin iMac inverter connection:
- iMac PSU pins 14 and 15 to the inverter pins 2 and 5 (12V power)
- iMac PSU pins 8 and 16 to inverter pins 4 and 6 (GND)
- LCD Driver board BL_ON to inverter pin 1 (ENA)
- LCD Driver board ADJ to inverter pin 3 (PWM)

The ENA and PWM signals would normally come from the iMac logic board, but now come from the LCD driver board.

I have also jumpered PSU pins 6 and 7 to turn on all the PSU functions (again, this would normally be done by the logic board).

Unfortunately, I get no backlight power.

In troubleshooting with the LCD driver board connected to the the 6-pin iMac inverter connector:
- Pin 1 (ENA) 4.94V. (EDIT - The required voltage for the ENA signal is 3.3V)
- Pin 2 (VIN) 12.02V
- Pin 3 (PWM) 3.06V. (EDIT - The required voltage for the PWM signal is 3.3V @ 13.3 kHz)
- Pin 4 (GND) 0.0V
- Pin 5 (VIN) 12.01V
- Pin 6 (GND) 0.0 V

All of the measurements above seem to be within expected range, although the PWM voltage may be a little low.

Searching online further about the PWM signal for the iMac inverter, it seems the PWM signal is supposed to be 3.3V with a frequency of 13.3kHz.

I then measured the frequency of the PWM signal coming from the LCD driver board to Pin 3 of the inverter and I get 36.03 kHz, which is almost 3x faster than the specification.

I am beginning to wonder if the problem most of us with the 2011 27 inch iMacs are having is due to the PWM signal of the LCD driver boards being too far out of spec for the iMac inverter?

Any thoughts about my hypothesis? I was thinking of buying an adjustable PWM controller to see if that would resolve the issue - (PWM controller) - but wanted to put this out to the forum to see if there might be something else I am missing.

Notes:
1. I do not suspect I have a faulty inverter board because it was fully functional immediately before I began the conversion 2 days ago.
2. I do not suspect I have a faulty display because it works with the supplied inverter board that came with the LCD driver, but it is dimmer than I want (as is common for most of us).

 

[gang-himself]

Today, I gave my 2011 iMac a new life as Display. I managed to use the original PSU and Inverter-board with the chinese controller working, BUT:
- Brightness is the wrong way, a higher value is less bright. Above values of 60, the backlight goes off completely.
- The apple inverter-Board immediately starts to smell, So there is something wrong, I guess with the PWM-Signal.
@SubDriver:
This could be explained by your measurements…

I changed back to the chinese inverter: Less brightness, but no smelling…

 

[SubDriver]

I am waiting to receive my dedicated PWM signal generator (expect it on 31 December). I will post an update of my findings and setup once I have it and I'm able to test my theory.

 

[csdesign3]

I am waiting to receive my dedicated PWM signal generator (expect it on 31 December). I will post an update of my findings and setup once I have it and I'm able to test my theory.

Im using my 2011 27 imac as a monitor since last year with Chinese boards, the only problem i tinhk its the PWM signal and voltage. See this article https://forums.macrumors.com/thread...e.1596614/page-55?post=26890535#post-26890535

 

[SubDriver]

Im using my 2011 27 imac as a monitor since last year with Chinese boards, the only problem i tinhk its the PWM signal and voltage. See this article https://forums.macrumors.com/thread...e.1596614/page-55?post=26890535#post-26890535

That post is what inspired me to try to use a PWM signal generator to replace the PWM signal from the Chinese board. Still working on it.

 

[SubDriver]

Success! I now have my 2011 27 inch iMac converted to a standalone display using both the original internal power supply and inverter. As expected, this solved the brightness issues of the constant current board that ships with the LCD driver board.

It took a long time to figure out why the iMac inverter wouldn't work with the LCD driver board. Ultimately, it was two things.
1. The PWM signal generator of the LCD driver board was not delivering the correct voltage or frequency. My inverter required the PWM signal to be ~3.3Vdc at 13.3 kHz. This was solved by placing a step down voltage converter and a PWM signal generator in series to feed the iMac inverter board.
2. The BLO (Backlight On) signal from the LCD driver board was not delivering the correct voltage to the "ENA" (Backlight Enable) pin for the iMac inverter. The LCD driver board was providing ~5Vdc, but my iMac inverter board required a 3.3vdc feed just like the PWM signal.

I used one of the 12Vdc lines from the LCD driver board to feed the voltage converter and PWM signal generator. Of the 6 lines coming from the LCD driver board, I am only using 2 of them (a 12Vdc line and a GND line). The BLO and ADJ lines are disconnected since those signals now come from the standalone sources.

The hardest part to figure out was the proper ENA voltage. Nearly everywhere I looked indicated that this line should be ~5Vdc. However, my backlight remained off even afer I connected the PWM signal generator to the iMac inverter board. After a bunch more digging online, I came across the schematics for the main logic board (MLB) for the 2009 27 inch iMac. The schematics showed the ENA signal was supposed to be 3.3 Vdc. I made an assumption that the inverter requirements for the ENA (or BL_ON) signal of the 2009 27 inch iMac were likely the same for my 2011 27 inch iMac. (Google "2011 A1312 imac main logic board schematic" and a few links should provide you options to view the schematics)

I will post some pictures of my modification and other details in the next couple of days. Besides the display, I also have the following installed in the iMac.
- 4 drives (2 SSD, 1 HDD, and the SuperDrive), all of which are functional and connect to a SATA-III to 5 Gbps USB 3.1 converter
- The step down voltage converter and PWM signal generator mentioned above
- Two crossovers for the iMac's internal speakers (actively troubleshooting this right now as I am getting no sound from the speakers which were functional before starting the conversion). Maybe my LCD driver board doesn't have an amplifier?

More to come soon.

 

[Nguyen Duc Hieu]

Success! I now have my 2011 27 inch iMac converted to a standalone display using both the original internal power supply and inverter. As expected, this solved the brightness issues of the constant current board that ships with the LCD driver board.

Maybe my LCD driver board doesn't have an amplifier?

More to come soon.

1. Congratulations on the Success!
2. The amplifier on the LCD driverboard is very weak. You can try driving the speaker drivers without any frequency divider first. If the sound are not very good, try the simplest frequency divider, which is only a 2.7uF connect in serial with the treble driver.
3. To amplify the speaker drivers with the market sold 2-step frequency divider you currently have, I guess you will need an additional amplifier board.