What components need replacing on the Logic board?

"Michael

@zookzook


Rep: 385




6


1


1"

"Update (28.02.2016)

my Cinema Display 24"" FIX :)

-------------------

Step 1: Remove the 3 resistors R0444,R0459,R0445

-------------------

Step 2: connect the 3 pull-down resistors to 3.3V (

ONLY the page to the driver IC)

-------------------

END FIX

-------------------

Have fun and viel Spaß ^^

-->!!WARNUNG /Warning !!<--

the L-board has 24& 70 voltage

**Nachbau auf eigene Gefahr,ich übernehme keine Haftung**"

"These are repairable, they use the same lg panel found in the 2011 27 inch Imac.

This repair is not for the average repair person.

As any apple repair person knows, (official or not!) the 2011 Imac had serious backlight issues.

Repair Information is sparse and difficult to find, not to mention the many (So bloody many!) people who refuse to believe you.

The repair is simple:

Thunderbolt display or Imac 2011 27 inch.

Check all functions before hand, rule out backlight driver, psu, cables etc.

Take out lcd panel, disassemble lcd panel, only as far as you need to to get at the backlight strip.

remove backlight strip, resolder 4 or 5 pin plug on backlight strip even if it looks clean.

This is a factory defect.

I am a computer technician in Australia who has to do these and other repairs that apple won't admit are issues fairly often."

"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.

(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 (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/328453350...

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

"here are some pictures of the Cinema Display

Here's the back of the logic board"