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Current version by: Frieder ,

Text:

Hi Guys,
 
I got an defective Apple Cinema Display for 150 bucks. There is a Picture but no backlight. I followed Michaels solution, many thanks for that btw.
 
I removed the two jumper resistors going to the led driver pwm inputs and shorted them to 3V. still no backlight. Well sure! The MCU is sending 3V to the third led driver connection - thus the led driver switches off as it thinks there is an error.
 
So i started from scratch to identify every of these three connections between the MCU and led driver. It turns out that R1133 and R1132 are the pwm signals for the led strips and R1135 is the “error/shutdown“ signal for the led driver!?
 
With power connected i took my measureing probes and carefully supplyed 3V to the pwm input of the led driver. both led strips where controllable this way - so the led driver is working.
 
[image|1868920]
 
[image|1868919]
 
[image|1868925]
 
[image|1868926]
 
[image|1868924]
 
(last picture shows the display with the old backlight leds - thus the color is a bit wrong -> yellow-/redish)
 
As shown in the pictures you can see the pwm signal in 3 states - LEDs off - 50% On - 100% On.
 
(controlled with my imac connected to the ACD)
 
So the MCU is also working BUT is sending 3V to the third connection… i gues that the mcu is doing the current sensing and is shutting down the led driver in case of overcurrent!?
 
So why is that…
 
According to Apple, the LG Panel in the ACD is given with a lifespan of 36000 hours. Its nearly 7-8 years old.. so most likely the panel is way longer in operation than 36000 hours. Especially because i noticed, that the display is half as bright as the same LG Panel in my iMac.iMac (with the transitional fix given below)

According to Apple, the LG Panel in the ACD is given with a lifespan of 36000 hours. Its nearly 7-8 years old.. so most likely the panel is way longer in operation than 36000 hours. Especially because i noticed, that the display is half as bright as the same LG Panel in my iMac.iMac (with the transitional fix given below)

 
Long story short: I ordered new backlight leds from aliexpress for about 10 bucks, replaced the old ones and now the display is as bright as my imac and working reliably.
 
 
 
So no software/mcu issue at all (for me at least).
 
 
 
For the dirty fix you can just remove R1135.. thus disabling the current sensing. One safety option less but full functionality. I did so to overcome the time until delivery of the new strips.
 
 
 
Link to the LG-panel LM270WQ1 led strips: https://de.aliexpress.com/item/32845335052.html?spm=a2g0s.9042311.0.0.35d44c4dX8D5Qt
 
 
 
i apologize for any spelling mistakes.. greetings from germany.

Status:

open

Edit by: Frieder ,

Text:

Hi Guys,
 
I got an defective Apple Cinema Display for 150 bucks. There is a Picture but no backlight. I followed Michaels solution, many thanks for that btw.
 
I removed the two jumper resistors going to the led driver pwm inputs and shorted them to 3V. still no backlight. Well sure! The MCU is sending 3V to the third led driver connection - thus the led driver switches off as it thinks there is an error.
 
So i started from scratch to identify every of these three connections between the MCU and led driver. It turns out that R1133 and R1132 are the pwm signals for the led strips and R1135 is the “error/shutdown“ signal for the led driver!?
 
With power connected i took my measureing probes and carefully supplyed 3V to the pwm input of the led driver. both led strips where controllable this way - so the led driver is working.
 
[image|1868920]
 
[image|1868919]
 
[image|1868925]
 
[image|1868926]
 
[image|1868924]
 
(last picture shows the display with the old backlight leds - thus the color is a bit wrong -> yellow-/redish)
 
As shown in the pictures you can see the pwm signal in 3 states - LEDs off - 50% On - 100% On.
 
(controlled with my imac connected to the ACD)
 
So the MCU is also working BUT is sending 3V to the third connection… i gues that the mcu is doing the current sensing and is shutting down the led driver in case of overcurrent!?
 
So why is that…
 
According to Apple, the LG Panel in the ACD is given with a lifespan of 36000 hours. Its nearly 7-8 years old.. so most likely the panel is way longer in operation than 36000 hours. Especially because i noticed, that the display is half as bright as the same LG Panel in my iMac.
 
Long story short: I ordered new backlight leds from aliexpress for about 10 bucks, replaced the old ones and now the display is as bright as my imac and working reliably.
 
 
 
So no software/mcu issue at all (for me at least).
 
 
 
For the dirty fix you can just remove R1135.. thus disabling the current sensing. One safety option less but full functionality. I did so to overcome the time until delivery of the new strips.
 
 
 
Link to the LG-panel LM270WQ1 led strips: https://de.aliexpress.com/item/32845335052.html?spm=a2g0s.9042311.0.0.35d44c4dX8D5Qt
 
 
 
i apologize for any spelling mistakes.. greetings from germany.

Status:

open

Edit by: Frieder ,

Text:

Hi Guys,
 
I got an defective Apple Cinema Display for 150 bucks. There is a Picture but no backlight. I followed Michaels solution, many thanks for that btw.
 
I removed the two jumper resistors going to the led driver pwm inputs and shorted them to 3V. still no backlight. Well sure! The MCU is sending 3V to the third led driver connection - thus the led driver switches off as it thinks there is an error.
 
So i started from scretchscratch to identify every of these three connections between the MCU and led driver. It turns out that R1133 and R1132 are the pwm signals for the led strips and R1135 is the “error/shutdown“ signal for the led driver!?
So i started from scretchscratch to identify every of these three connections between the MCU and led driver. It turns out that R1133 and R1132 are the pwm signals for the led strips and R1135 is the “error/shutdown“ signal for the led driver!?
 
With power connected i took my measureing probes and carefully supplyed 3V to the pwm input of the led driver. both led strips where controllable this way - so the led driver is working.
 
[image|1868920]
 
[image|1868919]
 
[image|1868925]
 
[image|1868926]
 
[image|1868924]
 
(last picture shows the display with the old backlight leds - thus the color is a bit wrong -> yellow-/redish)
 
As shown in the pictures you can see the pwm signal in 3 states - LEDs off - 50% On - 100% On.
 
(controlled with my imac connected to the ACD)
 
So the MCU is also working BUT is sending 3V to the third connection… i gues that the mcu is doing the current sensing and is shutting down the led driver in case of overcurrent!?
 
So why is that…
 
According to Apple, the LG Panel in the ACD is given with a lifespan of 36000 hours. Its nearly 7-8 years old.. so most likely the panel is way longer in operation than 36000 hours. Especially because i noticed, that the display is half as bright as the same LG Panel in my iMac.
 
Long story short: I ordered new backlight leds from aliexpress for about 10 bucks, replaced the old ones and now the display is as bright as my imac and working reliably.
 
i apologize for any spelling mistakes.. greetings from germany.

Status:

open

Original post by: Frieder ,

Text:

Hi Guys,

I got an defective Apple Cinema Display for 150 bucks. There is a Picture but no backlight. I followed Michaels solution,  many thanks for that btw.

I removed the two jumper resistors going to the led driver pwm inputs and shorted them to 3V. still no backlight. Well sure! The MCU is sending 3V to the third led driver connection - thus the led driver switches off as it thinks there is an error.

So i started from scretch to identify every of these three connections between the MCU and led driver. It turns out that R1133 and R1132 are the pwm signals for the led strips and R1135 is the “error/shutdown“ signal for the led driver!?

With power connected i took my measureing probes and carefully supplyed 3V to the pwm input of the led driver. both led strips where controllable this way - so the led driver is working.

[image|1868920]

[image|1868919]

[image|1868925]

[image|1868926]

[image|1868924]

(last picture shows the display with the old backlight leds - thus the color is a bit wrong  -> yellow-/redish)

As shown in the pictures you can see the pwm signal in 3 states - LEDs off - 50% On - 100% On.

(controlled with my imac connected to the ACD)

So the MCU is also working BUT is sending 3V to the third connection… i gues that the mcu is doing the current sensing and is shutting down the led driver in case of overcurrent!?

So why is that…

According to Apple, the LG Panel in the ACD is given with a lifespan of 36000 hours. Its nearly 7-8 years old.. so most likely the panel is way longer in operation than 36000 hours. Especially because i noticed, that the display is half as bright as the same LG Panel in my iMac.

Long story short: I ordered new backlight leds from aliexpress for about 10 bucks, replaced the old ones and now the display is as bright as my imac and working reliably.

i apologize for any spelling mistakes.. greetings from germany.

Status:

open