I was thinking the same thing regarding a separate amp... although I am not sure if it is worth trying to cram more stuff into the iMac. Heat generation will begin to become a concern at some point, especially for amplifiers.
Got a tip for us?
Let us know
Become a MacRumors Supporter for $50/year with no ads, ability to filter front page stories, and private forums.
Display brightness of my old iMac
- Thread starter zoran
- Start date
- Sort by reaction score
Hi @SubDriver,
Thank you for sharing such a detailed guide! I’m planning a similar modification and have already purchased the PWM module and step-down converter you mentioned. I have a quick question:
When you disconnected the BLO and ADJ signals from the LCD driver board, does the monitor still properly turn off when the connected computer goes into sleep mode or when the LCD driver decides to enter sleep mode?
@wujku It does not turn off when the LCD driver enters sleep mode. I tried to connect the BLO signal to a step down voltage converter, but it is not being recognized by the converter. I don't know why this is the case yet and plan to continue troubleshooting over time to attempt to resolve this.
Also, be sure to check the output voltage from the converter and the PWM signal generator. The digital displays are close, but I found them to be off by 0.1 or 0.2 Vdc. Frequency was a bit closer
For now, I am simply turning off the display anytime I get up and leave my desk. I installed a separate power button that fullly turns off the power supply to do this. See my next post for details....
Also, be sure to check the output voltage from the converter and the PWM signal generator. The digital displays are close, but I found them to be off by 0.1 or 0.2 Vdc. Frequency was a bit closer
For now, I am simply turning off the display anytime I get up and leave my desk. I installed a separate power button that fullly turns off the power supply to do this. See my next post for details....
Last edited:
I still have some details to add to the document (such as the PWM duty cycle setting - I have mine at 65-70%), but this should get most anyone looking to do a similar modificaiton started.
Last edited:
I suppose a 30W class-D amplifier board is basically smaller than the frequency divider you currently have.... And it uses 12V DC, too, which is quite convenient...
XH-A232 30w+30w Audio Dual Channel Amplifier Board Class D Bass MP3 Power Module | eBay
XH-A232 30w+30w Digital Subwoofer Amplifier Module Audio Speaker Dual Channel Board Bass MP3 Power Part Accessory. Power amplifier type: Class D. Number of channels: double channels. 1 x Amplifier Board.
www.ebay.com
@wujku I'm thinking a unidirectional logic level converter (see the sketch below) is what I need to use to restore the BL_ON signal functionality that is missing from my conversion (see post #78 above) instead of a routine step down voltage converter.
The 5V logic input would come from the BL_ON line from the LCD driver board.
The +3.3V power would come from adding a line from my existing step down converter (12V to 3.3 V) that is already being used to supply the PWM signal generator.
The 3.3V logic output line would connect to the ENA pin (Pin 1) on the iMac inverter board.
When the BL_ON signal is off (either due to sleep or turning the display off using the LCD driver controller board button), it sends 0V to the logic level converter and thus has 0V for the output.
When the BL_ON signal is on, it sends 5V to the logic level converter which then triggers the 3.3V output to be sent to the ENA pin on the inverter.
Problem is finding a unidirectional converter that is already mounted to a PCB.
May have to use to a bidirectional converter and wire it for unidirectional functionality. This is perfectly acceptable but will require a 5V power feed that I do not presently have in my setup. The bidirectional converters require power on both sides of the converter chip.
The 5V logic input would come from the BL_ON line from the LCD driver board.
The +3.3V power would come from adding a line from my existing step down converter (12V to 3.3 V) that is already being used to supply the PWM signal generator.
The 3.3V logic output line would connect to the ENA pin (Pin 1) on the iMac inverter board.
When the BL_ON signal is off (either due to sleep or turning the display off using the LCD driver controller board button), it sends 0V to the logic level converter and thus has 0V for the output.
When the BL_ON signal is on, it sends 5V to the logic level converter which then triggers the 3.3V output to be sent to the ENA pin on the inverter.
Problem is finding a unidirectional converter that is already mounted to a PCB.
May have to use to a bidirectional converter and wire it for unidirectional functionality. This is perfectly acceptable but will require a 5V power feed that I do not presently have in my setup. The bidirectional converters require power on both sides of the converter chip.
Last edited:
@SubDriver
Reading your debugging of the whole B/L chain, I've been wondering how the use of the DZ-LP0818 board made to go with the R1811 5K converter board might function with the Chinese 2K converter board?
One difference may be that the LP0818 seems just to require an up to 5v DC signal on its BL_ADJ pin (and 3.3V on/0V off on its BL_ON). So there isn't any mention of PWM on the R1811's data specs.
The LP_0818 seems to only need 3.3v on its enable pin, so I've used that value for the R1811 output above, the data sheet just says ON.
So I'm not clear if the Chinese inverter board outputs PWM, which might not work with the LP0818?
Or maybe the R1811 is actually supplying a 0-5v PWM signal to adjust backlight intensity?
Which is not mentioned in the data sheet.
The iMac 2k screens seem to get the same B/L voltage* as the 5K ones, but there are less B/L feed wires (so less LEDs?), so maybe needs less current...
* Probably needs confirming?
Reading your debugging of the whole B/L chain, I've been wondering how the use of the DZ-LP0818 board made to go with the R1811 5K converter board might function with the Chinese 2K converter board?
One difference may be that the LP0818 seems just to require an up to 5v DC signal on its BL_ADJ pin (and 3.3V on/0V off on its BL_ON). So there isn't any mention of PWM on the R1811's data specs.
The LP_0818 seems to only need 3.3v on its enable pin, so I've used that value for the R1811 output above, the data sheet just says ON.
So I'm not clear if the Chinese inverter board outputs PWM, which might not work with the LP0818?
Or maybe the R1811 is actually supplying a 0-5v PWM signal to adjust backlight intensity?
Which is not mentioned in the data sheet.
The iMac 2k screens seem to get the same B/L voltage* as the 5K ones, but there are less B/L feed wires (so less LEDs?), so maybe needs less current...
* Probably needs confirming?
Last edited:
@PaulD-UK
I am confident the Chinese LCD driver board outputs a PWM signal. I measured it a 3.06V with a frequency of 36.03 kHz (see post 69 above). Since most (maybe all?) of the 5K LCD driver boards have the inverter board functionality built in, it would be logical for the PWM functionality to also reside on the driver board itself - I will test this when I convert my 5K iMac in the next month or so. I need to ensure this 2K iMac screen is fully ready to go as a stand-in for the 5K iMac screen before I start the 5K modification. I will be purchasing a JRY--SA1 board for my 5K modification.
I don't think the constant current boards control the PWM signal. I think they are primarily for signal conditioning of the power driving the displays. But that is simply my best engineering guess after doing all the debugging for the 2K display mod.
I am confident the Chinese LCD driver board outputs a PWM signal. I measured it a 3.06V with a frequency of 36.03 kHz (see post 69 above). Since most (maybe all?) of the 5K LCD driver boards have the inverter board functionality built in, it would be logical for the PWM functionality to also reside on the driver board itself - I will test this when I convert my 5K iMac in the next month or so. I need to ensure this 2K iMac screen is fully ready to go as a stand-in for the 5K iMac screen before I start the 5K modification. I will be purchasing a JRY--SA1 board for my 5K modification.
I don't think the constant current boards control the PWM signal. I think they are primarily for signal conditioning of the power driving the displays. But that is simply my best engineering guess after doing all the debugging for the 2K display mod.
@SubDriver ”…the 5K LCD driver boards have the inverter board functionality built in, it would be logical for the PWM functionality to also reside on the driver board itself…”
All the on-board B/L circuitry is marked as NC in the R1811 data sheet when the external CC board is connected, so I think all the functionality is transferred to the LP0818 when it is connected.
Except the signal the R1811 outputs on BL_ADJ, which may or not be PWM.
But the data sheet doesn’t say that, only 0-5v…
All the on-board B/L circuitry is marked as NC in the R1811 data sheet when the external CC board is connected, so I think all the functionality is transferred to the LP0818 when it is connected.
Except the signal the R1811 outputs on BL_ADJ, which may or not be PWM.
But the data sheet doesn’t say that, only 0-5v…
Last edited:
@PaulD-UK "ll the on-board B/L circuitry is marked as NC in the R1811 data sheet when the external CC board is connected, so I think all the functionality is transferred to the LP0818 when it is connected."
I agree that the B/L circuitry flows from the LCD driver board to the constant current board. However, I don't think the constant current board fully replaces these signals. I think it simply amplifies and conditions the feed from the LCD driver board to improve the overall performance. The actual control of the signals remains with the LCD driver board.
By my read of the LP0818 spec sheet below, I see the following:
BL_ON is represented by the the "Input Voltage ON/off control" line and the "Input Current" line.
BL_ADJ is represented buy the "Brightness control current" line, with two values for Vadj (0V and 5V). This certainly looks like a PWM to me, with the duty cycle between the 5V and 0V signal controlled via the LCD driver board on screen display Brightness slider.
I agree that the B/L circuitry flows from the LCD driver board to the constant current board. However, I don't think the constant current board fully replaces these signals. I think it simply amplifies and conditions the feed from the LCD driver board to improve the overall performance. The actual control of the signals remains with the LCD driver board.
By my read of the LP0818 spec sheet below, I see the following:
BL_ON is represented by the the "Input Voltage ON/off control" line and the "Input Current" line.
BL_ADJ is represented buy the "Brightness control current" line, with two values for Vadj (0V and 5V). This certainly looks like a PWM to me, with the duty cycle between the 5V and 0V signal controlled via the LCD driver board on screen display Brightness slider.
Given the specs above, it might be possible the BL_ON to ENA signal from the LP0818 would work with the iMac inverter board.
But the BL_ADJ to PWM signal doesn't look promising. The peak voltage for the iMac inverter board is 3.3Vdc and the LP0818 appears to be delivering 5Vdc. And since it doesn't provide details about the PWM frequency, it is even harder to assess.
But the BL_ADJ to PWM signal doesn't look promising. The peak voltage for the iMac inverter board is 3.3Vdc and the LP0818 appears to be delivering 5Vdc. And since it doesn't provide details about the PWM frequency, it is even harder to assess.
After some additional research into various options to restore my audio and BL_ON signal functionality, here is my plan:
1. Add a 12Vdc to 5Vdc step down voltage converter to supply power to the following items:
2. this audio amplifier board before the crossovers (Note it uses a 5Vdc input)
3. this bidirectional logic level controller board into the BL_ON signal path and apply 5Vdc power on same side as the BL_ON signal from the LCD driver board and 3.3Vdc power (from my existing step down voltage converter) on the other side with the wire connected to the ENA pin on the iMac inverter
Additionally, I am probably going to install a temperature controlled fan beneath the iMac inverter board. The back of the iMac case behind the inverter does get fairly warm, although not too hot to touch. However, the board itself is likely much warmer so I think a small fan blowing up through the inverter is a good precaution. Additionally, I plan to reinstall the iMac HDD fan since I have room for it and the temperature controller provides for independent operation of two fans.
1. Add a 12Vdc to 5Vdc step down voltage converter to supply power to the following items:
2. this audio amplifier board before the crossovers (Note it uses a 5Vdc input)
3. this bidirectional logic level controller board into the BL_ON signal path and apply 5Vdc power on same side as the BL_ON signal from the LCD driver board and 3.3Vdc power (from my existing step down voltage converter) on the other side with the wire connected to the ENA pin on the iMac inverter
Additionally, I am probably going to install a temperature controlled fan beneath the iMac inverter board. The back of the iMac case behind the inverter does get fairly warm, although not too hot to touch. However, the board itself is likely much warmer so I think a small fan blowing up through the inverter is a good precaution. Additionally, I plan to reinstall the iMac HDD fan since I have room for it and the temperature controller provides for independent operation of two fans.
As an Amazon Associate, MacRumors earns a commission from qualifying purchases made through links in this post.
Congrats
when you can please share more info or pics.. i'm using mine 2011 for one year and really want to solve the brightness issue for goodi added 2 crossover boards buyed from aliexpress ( https://pt.aliexpress.com/item/1005..._main.179.188ccaa4gnWyIC&gatewayAdapt=glo2bra ), right now its has good bass and treble.
@csdesign3Congrats
There is an initial document attached to post 79. I am working on a more detailed revision now and hope to have it done in the next day or so.
We are very happy today, you help solve an old problem for the community. Someone had publish some good results but without further information or photos. Thank you again for the great work. I will soo try to replicate your results too
I've done some research about the crossovers in your pictures. They are designed for high-power amp. Therefore I suppose you have 2 options below:
1. Using high power amplifier board.
2. Fiddling with the jumpers to see if it changes anything. There are 4 jumpers on the board (A/B/C/D), designed for boosting sound of low/high frequencies.
I assume that you connected the correct speaker drivers (bass/treble) to the crossover output...
As an Amazon Associate, MacRumors earns a commission from qualifying purchases made through links in this post.
after your conversion, can you adjust brightness via Chinese controller board menu?
@Nguyen Duc Hieu ”2. Fiddling with the jumpers to see if it changes anything. There are 4 jumpers on the board (A/B/C/D), designed for boosting sound of low/high frequencies.”
I’ve also had a look at what those jumpers do, and more importantly, can’t do….
I’ve also had a look at what those jumpers do, and more importantly, can’t do….
@csdesign3
No. However, there are two potential solutions to provide this functionality.
1. Use software such as Monitor Control (or Monitor Control Lite - Free in the App Store) or Better Display to control the brightness. (This method adjusts the video signal from the GPU instead of changing the actual PWM duty cycle like the controller board menu)
2. Install two additional push buttons in the iMac case (momentary style push buttons instead of latching pushbuttons) and connect them to the duty cycle button connections on the PWM board. This will allow direct changing of the PWM duty cycle without the need to use the controller board menu. This is similar to how the original iMac power button can be wired to the controller board power button to turn the display on/off.
I plan to use option number 2, but haven't yet had the time to do this. Hopefully soon...
Yep...
or Option 3, get differnt crossovers... I am gonna see if they work with the 3W amps I bought first. I did test them connected to the headphone jack of my MacBook Pro and the crossovers and iMac speakers worked fine. This is why I think my LCD board amp is simply extremely weak or doesn't exist at all...
Last edited:
My LCD controller board(i think) its the same has yours, at level one of volume connected to HDMI its very audible at night (exemple when using Xbox Series S i can ear clearly the menu sounds), i might attenuate the sound output with a cap. On PC side via DP-Port its a good level.
Last edited:
Humm, maybe this could be a potencial solution for the problem:
1 - A potencial solution and can use the OSD menu on chinese board but less details about to makeit (See Frédéric R Posted: Jun 27, 2023 post on that thread) https://www.ifixit.com/Answers/View/519667/iMac+Intel+27"+EMC+2429+Power+Supply+voltage+values
2 - A Good guide but not a perfect solution
https://medium.com/@fixingthings/im...lcd-pwm-brightness-with-an-esp32-bc32da61a0e7
After you see both potencial solutions, give me your opinion please.