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Black... No Display but power/sound/etc. is fine
All blogs read Replace one of the following:
•Power Supply
• Logic Board
• LCD Panel
Since Im getting power Ive ruled out the power supply.
Next, on to the Logic board.
What needs to be checked? Capacitors?
Please confirm the most likey suspects.
Thanks
Bu iyi bir soru mu?
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Jason, this is not as easy as just recommending a certain part that has failed. You do want to check your logic board over and see if you find any bulging or leaking capacitors. Just because the power /sound/etc. may be there, you can also not rule out the power supply. It may not supply the power to the LED backlight. You will need to check on that as well, take a good luck on the logic board. There should also be a fuse for the backlight, which may have failed. Post a couple of hi-res images of your logic board with your question, so we may look at it and see if we can come up with something more concrete. I would also suggest that you try the Apple Deep Dive for Blank / No Video, No Backlight:
Check Result Action Code
1. Connect display to AC power source. Connect Mini DisplayPort, MagSafe and USB
connectors into a known good, supported, powered-up portable. Verify display’s USB
hub and built-in camera are listed in the System Profiler’s USB device tree.
Yes
Power is available to the display logic board, and USB communication working.
Go to step 2.
No
Go to Dead Unit/No Power.
2. Unplug and replug Mini DisplayPort connector into a known-good, supported, powered-up portable system and monitor the portable’s display. Verify that the
portable’s display briefly turns off then back on.
Yes
LCD is powered and detected by system. Go to step 7.
No
Suspected no power to LCD panel or no DisplayPort connection with system. Go
to step 3.
3. Remove glass and LCD panel screws, slightly pivot LCD panel and verify that the internal DisplayPort cable (part of all-inone cable) and function cable are fully connected to LCD panel and logic board.
Yes
Go to step 4.
No
Reseat DisplayPort connection to LCD panel and/or function cable connections between logic board and LCD panel and retest.
If issue persists go to step 4.
For any damaged cable, replace affected cable before testing again:
- all-in-one cable.
- function cable.
4. Unplug and replug Mini DisplayPort connector into a known-good, supported,
powered-up portable system and monitor the portable’s display. Verify that the
portable’s display briefly turns off then back on.
Yes
LCD is powered and detected by system. Go to step 7.
No
Suspect no power to LCD. Replace function cable and retest. If issue persists go to
step 5.
5. Replace all-in-one cable and reinstall LCD. Unplug and replug the Mini DisplayPort
connector into a knowngood, supported, powered-up portable system and monitor
the portable’s display. Verify that the portable’s display briefly turns off then back on.
Yes
LCD panel powered and detected by system. Go to step 7.
No
LCD panel still not detected by system. Suspect no LCD power from logic board.
Go to step 6.
6. Replace logic board and reinstall LCD. Unplug and replug the Mini DisplayPort
connector into a knowngood, supported, powered-up portable system and monitor
the portable’s display. Verify that the portable’s display briefly turns off then back on.
Yes
LCD panel powered and detected by system. Go to step 7.
No
LCD panel still not detected by system with replaced function cable, all-in-one cable and logic board. Suspect LCD panel video input damage.
Replace LCD panel.
7. If the Blank/No Video/No Backlight issue persists, darken room and connect to a knowngood supported system. Verify backlight is present by looking for faint glow from display.
Yes
LCD panel powered, detected by system and backlight is ON but there is no video on LCD. Replace LCD panel.
No
LCD panel is detected by system but no backlight. Check whether video is present on LCD. Go to step 8.
8. Shine bright (low heat) flashlight into the front of the LCD. and verify if any image is
being displayed.
Yes
Video is present, so issue is only with missing backlight. Go to step 9.
No
No image displayed on LCD Replace LCD panel.
9. Remove glass and LCD panel screws, lift LCD panel to verify that the function cable, and LED backlight driver cable connections are secure. See Functional Overview.
Yes
If connections are OK and secure and there is still no backlight, go to step 10.
No
If any cable is damaged, replace affected cable and retest:
- function cable
- LED backlight driver cable (part of LCD panel)
10. Remove LCD panel. Set digital multimeter to DC and correct range, and verify that a 23.3–25.7 V DC voltage is present between logic board test point (24 V DC) and chassis ground (GND).
Yes
24 V DC power for backlight is present on logic board, but no backlight. Suspect no
V-sync signal coming to logic board. Go to step 11.
No
No 24 V DC present for LED backlight power. Replace power supply.
11. Replace function cable and retest. Verify that the no backlight issue is fixed.
Yes
Defective function cable prevented backlight from being enabled by logic board.
No
Go to step 12.
12. Verify if the LED backlight driver cable (part of the LCD panel) has any signs of pinched or shorted wires. Also remove the logic board and verify if one or more of the three square inductors or adjacent components on top of board show signs of overheating.
Yes
LED backlight driver cable on LCD panel found damaged. Replace LCD panel, (make
sure that you don’t pinch the LED driver cable from LCD panel) and retest. If the no backlight issue persists after LCD panel replacement, replace logic board (LED backlight output from logic board had been damaged by shorted cable.)
No
Suspect no LED backlight output from logic board: go to step 12.
13. Replace logic board and verify that the no backlight issue is fixed.
Yes
Defective logic board LED backlight driver output.
No
Replace LCD panel.
Before you go and replace anything let us know what you found. Hope this helps, good luck.
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I replaced my power supply after seeing the screen on but no black light. Its not working still, Now i am returning the power supply i bought and going to buy the logic board if that doesn’t work I will throw this monitor in the trash.
@Tyler Brown, by just replacing the PSU you will not fix the backlight components. Do you have any board level experience, the tools to do some board level repair?
I have very limited experience with a soldering gun but youtube has some good videos for learning. What do i have to look for. I can purchase any tools i will need btw.
Okay start of by telling us the serial number to your computer. With that we can get the description of the hardware. Your PSU was ruled out since you have a new one. Tell us exactly what your computer does (or does not ) do. Also, let us know what you have done so far.
Ok about to start the project again. The computer I hook it up to is a MacBook Pro mid 2012. The monitor will flash sometimes from the initial plug in then stay black. I know it's knot the PSU because I replaced it like I said above. I am now going to try replacing the logic board. Btw when I shine a flash light I can see that the LCD is displaying my computer screen just no black light.
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Before you choose this solution, keep in mind, there are many problems that cause no backlight. For example the mosfet, coil and diode components may be broken. In this case the driver detects a failure (with the feedback resistor) and turns off. In my case everything was right. The microcontroller doesn't provide the PWM signal. But it took a long time to get this information. First I measured the signals on the board. Is the driver enabled? What is the input value of the PWM (S1 and S2) pin. I also checked (with the help of the data sheet) the mosfets, coils and diodes: Which pin of the driver is connected to the gate of what mosfet and what kind of function does it have? In the end I found out, that the external components are ok, so I began to make some tests with the driver!
In the image
100% pwm signal
you can see the little wire that put the 3.3 voltage as input for the pwm signal. The backlight turns on and the cinema display is alive again!
After four years of using the backlight of the LED Cinema Display 27" was turned off. First the backlight was very low or was flickering while trying to dim the display via the system panel. I turned the display off and on and then it was dark.
With the help of a torch light I saw a faint image of the desktop. USB and magsafe were working as well. So the display is working without the backlight.
First of all I teardowned the display like it shown in Teardown Apple Display
The interesting parts are
The led driver (called HV9982) is responsible to drive the leds stripes with current. It cares about the right current, because LEDs require more precise current management. The data sheet of the HV9982 you can find some basic information about the driver and this function:
HV9982 is a three-channel, closed loop, peak-current mode PWM controller designed to drive a constant out- put current. It can be used for driving either RGB LEDs or multiple channels of white LEDs.
In the next image you can see the led driver with its external components:
the led driver
Using the datasheet of the led driver we get some interesting facts about the pins:
the pins of the led driver
The led driver is controlled by the microntroller in the next picture:
the microcontoller
The controller turns the led driver on if the computer is connected via thunderbolt cable. With a multimeter you can measure a 3.3 volt signal on pin 10 (enabled). If the computer is unplugged then the signal is bound to ground. But be aware the is only litte space between the pins! Keep an eye on it to avoid short circuits! (To be honest, I did three short circuits, one hurts a bit and one does a nice spark.)
With the multimeter you can track the connections from pin to pin. I found out that the microntroller is connected to the pin 10 (enabled) and the pwm pins (17,18,19). The S1 and S2 pin are bound to ground and that means that the led driver is driven in the PWM mode. With the help of an oscilloscope I found out that the microcontroller does not send a PWM signal. He turns the led driver on but "forget" the create the PWM signal. In this case the backlight stays dark without any light. And you think the display is broken. (see for PWM)
But we have some luck! We can bridge the signal to 100%. We just connect the PWM pins to logical one and that is 3.3 volt. I found a pad that give me the 3.3 voltage and the pwm pins from the microcontoller are bridget by three 0 ohm resistor (labeled with R1132, R1133 and R1135). You cannot just put 3.3 volt to the pwm pins because they are connected with the microcontroller. This would cause a short circuit. In the following image you can see how the microntroller is connected to the pwm pins of the led driver:
the connection the the pwm pins
The "R1" is a pull down resistor which is used the put a logical 0 to the pwm pins if the microncontroller does nothing. Now we make the following connection:
the modified schema with constant 100% PWM
The led driver is a three channel pwm controller and the board contains all components for three channels and the connector is prepared for three channel but channel three is not used! So don't put 3.3 ohn R1133! In this case the led driver detects an error and switch off. The led cinema display has only two led stripes! Therefore connect only R1135 and R1132 with 3.3 volt.
So what do you think now? The problem is not a hardware problem, it is a software problem. The software within the microcontroller won't create the pwm signal. Unfortunately we don't have the source code, so we are not able to patch the firmware. We just cut the connections from the microcontroller and send now a pwm signal about 100%. You aren't able to dim any more and you needn't buy a new one! Is this a software error or just a hint that you should buy a new display?
the 3.3 volt pad and the 0 ohm resistors
Good luck! Please keep in mind:
PS: It was the **third display** where the backlight turns out. Unfortunately I didn't check them and they are trashed, because the local apple dealer said, that repairing is too expensive than buying a new one!
full backlight again
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Well done !!!!! , you did all that without a boardview and schematic? Are you positive the driver is not a QFN?
Having repaired several hundred of these units and advising as to source, I would say that the implication that a software bug or intentionally timed failure is ludicrous. The processor does vary the signal but as a protective measure as I have described numerous times before. The case of an momentary flicker and viewable unlit panel operation is not solved by a replacement board because the problem is not on the logic board. A new logic board is relatively inexpensive and the monitors were worth it to a point recently but wouldn't help this problem. The same can not be said for the power supply. So much misinformation on these monitors that real information gets buried. A fix for the power supply under load problem would be your "next" step. Of course, repairing the board you have now altered will be an interesting challenge of your soldering skills.
Hi John,
yes, I do it without any schematic. Just checked some connections with a multimeter and the data sheet of the driver. The driver is a QFN chip but you can touch the solder pads and that is some what thrilling because you can very easily connect to pins. For example: the enabled pin is next to VDD and VIN.
Hi Hedrickja,
there are some firmware updates for the cinema display (https://support.apple.com/de_DE/download...). So a software bug is not so ludicrous, I think. Maybe they learnt from Volkswagen. I don't know, but the led cinema display is working again now. If I ask the local apple dealer for new logic board it took always 800 €! So my company decided to buy a new display. We got three cinema display and the backlight of all them turned off after the extended warranty time.
<quote>
The processor does vary the signal but as a protective measure as I have described numerous times before
<quote>
That is interesting, but where did you described this?
I don't know what 800 ? is but new ones are avail. for $120 US in factory packaging. I paid about $99 retail for the last one I bought. It would not help you anyway. Also, with the monitors that are available now, repairs are becoming non-economical. Yes, there are always firmware revisions along the dev path but not ones that effect a failure years later. If Apple were to plan a failure like that and some disgruntled employee or reverse engineering tech were to discover or disclose it, it would be financial and marketing SUICIDE. The Volk debacle was a decision to try to salvage a serious dev problem instead of getting fired for failing to bring to market, not build their cars to fail miserably right after the warranty period. There were a small group of people desperate from their failure to solve a design problem. Placing a kill code in the monitor is much more devious and Apple consumers would recognize that. Risking their entire company just to sell a few more monitors. I think not.
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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**
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Hi Willi! This looks great!
thanks to their idea with the PWM Bypass ^^
Dear Willi, thanks for your work n the 24 inch display.
Not speaking german, i would greatly enjoy if you detail a bit your steps.
First you remove the three resistors
Then you bring 3.3v to where?
Thanks by advance.
Dav
Fix done today. works like a charm.
danke Willi
danke danke danke :)
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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.
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Hi John, good to know you are in Australia. Where are you located?
state of Victoria.
That's awesome. Would you be able to contact me as I have one without backlight, well, sometimes it still lights up and later goes blank. I wonder if I can fine someone for help. Cheers
I have an LED cinema display 24" from 2009, I have excatly the problem that the screen blanks out after a 1 sec flash of the image (prob. LED driver signal turns down). I was about to try the bypass solution above for the 3.3V drive input, but then wanted to ask first if the same backlight strip probem problem could be on my LED Display as well, because I would not want to loose the dispay dimming possibility. THanks in advance, robertnawfal@hotmail.com
I Did disassemble my display down to the Background lights, but I did not do any soldering yet.
Hey Robert Nawfal, where are you located currently?
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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.
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Hi, good work!
do you have a link for the LEDs you purchased.
Thanks
I was just about to ask the same question.
Awesome guy! Grüße aus Leipzig! Ich hab hier übrigens noch ein kaputtes iMac Logicboard, was ich eigentlich nach England schicken wollte, aber immer noch nicht gemacht habe. Kannst du das reparieren? :D
Link added to the post :)
@bvrulez Klar kein Problem. Schreib mir eine Email an frieder.blumenthal@icloud.com
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I had the same problems. Backlight was gone or very low.
The short story: I found out that the micro controller does not send the PWM signal to the LED driver.
Very mysterious! I checked the LED driver components (Mosfett, diode), I read the data sheet to understand the function of the HV9982 (LED driver). In the end there was no hardware problem there. If I connected the computer the micro controller enabled the LED driver but "forget" so send the PWM signal, so the LEDs stayed off.
Mmmm...maybe this is a software error or Apple wants to tell me to buy a new one? So I bridged the PWM input pins with a little wire connected to a 3.3 V pad (which I found about 1 cm around). Nice that die PWM output pins of the micro controller were bridged by 0 ohm resistors, so I could remove same and cut the connection from the micro controller. And then I got full backlight again. Of course I am not able to dim the backlight anymore.
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My Apple LED Cinema Display 27" is still up and running.
Hello Michael! Do you know anything about the thunderbolt display? Mine has the same symptoms, but the board is different. I was able to locate the indicated pins, but I did not find any 3.3v pad. Sorry for my english, I'm brazilian and I'm using google translate hoho
after the fix my display works but it went very very hot on the bottom of the screen ?
do Sony I experience this ?
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I just want to thank everyone in this post, especially Mike and Willi for all the knowledge and effort. Here's mine and Willi's fix worked perfectly.
Mine is a 24 inch Apple Cinema Display. It was completely dark, although the fan was spinning, Megasafe was charging, USB worked, and the MacBook Pro's monitor briefly turned on and off while the Apple Cinema display flickered very briefly. I followed the service manual and found that very very dimmed image can be seen on the Apple Cinema when shining a flash light to it, this is a confirmation that the back light wasn't functioning properly. After getting a reading of 24v when testing TP81 in relation to the chassis ground, I decided to go with Willi's fix and gave it a shot (note that I'm not an electrician nor electrical engineer). And it worked, although the soldering was very difficult for me. As Willi said, remove R0444, 0445, and 0459, connect the three pull down resistors to the 3.3v (L0631?).
And here's a link to the service manual if anyone is interested:
https://www.manualslib.com/manual/685572...
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I don't mean to offend anyone but you all seem to have missed the blatantly obvious and that is the LED backlight array.
LEDs age, and as such the amount of light that is emitted reduces. The LEDS in the LM240WU6 panel are made by Lumileds which is a subsidiary of Philips who in turn produced the panel under license from LG. The LEDs used are LXML-PWN1-0120 which should be operated at a forward voltage of between 3.0V & 3.6V @ 350mA and have a stated 39000 hours of life.
LEDs operate in constant current mode that is the current through the device is adjusted by altering the voltage across it. In low current LED applications this done with a simple resister. In high powered applications this is done with a controller chip such as the HV9982. Most high powered applications work as a closed loop system, that is they monitor the current flowing in the LED string and adjust the voltage across the string accordingly. The circuit Apple adopted does just that, it monitors the voltage developed across a low ohm resister in the bottom of the LED string and adjust the PWM signal to the HV9982 that will adjust the voltage to the LEDs. The suggested fix above of applying 3.3V to the PWM input will remove this feedback and will apply maximum voltage across the LEDs and is likely to result in damage to the LEDs and driver circuit.
What most people are experiencing is the backlight driver circuit shutting down due to it reaching an overvoltage point as it tries to pump more current through the aged LEDs.
The above plot shows the current through each LED with a forward voltage of 3.3V. As you can see there is a lot of variation (LED 1 shows as 0mA), none of them get near the 350mA that they should.
Conclusion, the only long term way to fix this problem is to replace the LED string as a whole or at least the weaker LEDs. The individual LEDs are available from DigiKey but they will prove difficult to replace as they are surface mount and are tied to a heat sink back plate. An alternative is to retrofit a low voltage backlight replacement string, they are available on eBay for as low as £4. These will require a 12V supply and will need to be turned on and off manually.
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Thanks James, Your answer makes a lot of sense. That would definitely explain my problem as well, since I noticed as well that couple of my LEDs are unfunctional (I disambled the whole display). I can still operate the display normally, but sometimes the LED control circuitry kicks in and shutsdown the backlight. Thanks a lot for the answer I have learned a lot during this little excursion to apple displays.
Hi James, can you tell me how you got the led info, and do you know of anywhere that would supply them/manufacture them. Any info would be appreciated, thanks.
Dan
I had an ACD with a similar issue - replaced the backlight strips with ones found on ebay from China. Now the monitor works perfectly.
Where could i buy those led strips for 24“ A1267 cinema display? I ve searched all over ebay and alibaba. I found only 27“ led strips.
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Have already forgotten about my 2009 ACD 24", it was standing around and getting dusty for 3 years now since it gets dark screen - thought thats it, no more spendign money, no time and no idea how to fix it ... In the last days I decide to give it a try after reading all yours comments and promising results. thanks for that!
When I bridged the resistors together R0821, R0804, R0896 and 3.3V it starts flashing like some described before... So I remembered this fault behaviour is shown by LED elsewhere when flashing is caused by overheating. While I disassemble the LG LCD unit, I was astonished about some sort of soot on the screen inside, maybe because of the mirror foil was getting crusty, baked all around the thin aluminium rail with LED on it...
Finally I decided to connect the 3.3V to the resistors separately. R0821 and R0804 are still flashing, but it works well for R0896! In conclusion only one of the 3x20 strings on the LED-rail will work, thats not that bright but sufficient and great for night shift.
Has anyone thought about replacing for a 12V-strip (60-LED-3528) ? Similar to someone's mod for older ACDs with CCFL-lamps I found on the internet
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Same result.
4 cinema display in my office: 1 OK with this FIX, 3 have flickering.
I'll try to connect 3.3V to single resistor soon...
I don't see solutions with this display.
Note: I buy new driver CHIP: i want to try to change this piece... but now I suppose the problem is led string..
BUT.. I can to try to SWAP good display (from the unit that working OK) to defect unit (with flickering) to check display... I'll try this ASAP
@rokost: I try to connect 100% good display (perfect working on the repaired display) to other units with flickering (and fix).
Result: the flickering persist!!
So I suppose that the LED board is OK but driver CHIP is damaged..
Maybe you are right about the faulty driver unit... Back then I had some different mysterious backlight dying issues on my 2008 MacBook Aluminium. First the keyboard light stopped working, later than display backlight too, but not at the same time. It was still usable for a desktop only, but I decided to replace the logicboard and it runs again perfectly.
THANKS @rokost!! Reading your comment I could fix my 24" Led Display! I understood that the three R08 resistors are the three led stripe lines, I kept having flickering after trying one, the first two and all three resistors, so I ended up trying one by one, in the end I skipped R0896 and just connected the last two (R0804 and R0821) to the 3.3v line and it worked!! So, my suggestion to anyone else with this problem, keep trying resistor combinations until you get a steady image. THANKS AGAIN! Paid $30 USD for this monitor and now works great! (no brightness control tho, but who cares!)
[image|730250]
Hi
thank you for this great tutorial, I have done exactly as you've shown and I still have no black light and in fact the I can see the display when I use a touch but now it is flickering with no back light. Whilst before I could see an image but the display was not flickering. Can you please help me as it is urgent
thank you
Sam
=== Update (21.12.2015) ===
Please see attached photo
[image|730250]
=== Update (21.12.2015) ===
can you see the photo
=== Update (21.12.2015) ===
Hi the led driver you are referring to is it the small board that is attached to the LG screen where the function cable, heat sensor etc is connected to?
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so i got yesterday a 24 inch cinema monitor for free (someone was close to put it in the trash….) where backlight sometime worked and sometime not.so i tryed the fix from willi and monitor flickered. so i jumped only R0804 and R0896 to the 3.3V rail and voila the monitor works again :)
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The problem on this 24 Cinema (and also on 27 Cinema and 27 Thunderbolt) is NOT the board but LED stripes. The rail mod is temporary solution. You have to change LED Stripes (2 led stripes on 27 inchs, they are the same used in iMacs 2011 panels) or single 24 inch led stripe.
It's possible to reflow the LED stripes, this work usually is more durable.
Soon I'll publish some article about this work.
Regards
Carlo
I have an extra 27 inch led stripes to sell that I accidentally ordered when searching for 24 inch model!
Hi @geiti94 I had to create an account just to comment that YOU FIXED IT FOR ME!
I bought this display for 50 bucks on the off chance I could fix it, and it turns out the previous owner had already tried willi's fix. I was sold this display with "constant flickering". I redid the jumper cable from only R0804 and R0896 to the 3.3V rail (left out R0821...I think?) and it flickered for like 30 seconds but now it is working perfectly.
Thank you so much for taking the time to leave your comment.
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I have the same issue on my 27 LED cinema display, it stays dark when reconnecting, sometimes i can reactivate it by switching power off and disconnect the video cable, than powering on and connecting it again. But this trick is working worse and worse over time. Today it didn’t work at all.
I already tried:
UPDATE 1:
It turned out that the Backlight LED stripes I ordered from aliexpress were not new ones, but used ones! (I overlooked it when i bought them!) So I’ll finally try to resolder the outer connectors on my old ones (as suggested by John) and see if this brings light back into the dark. (I’ll post another update when done.)
UPDATE 2 (FIXED!):
I finally resoldered the two connectors of the LED backlight stripes and put them back into the Panel… It seems to work perfect again. No Black screen, full brightness. I have to admit that changing the LED backlights of this panel is a nightmare. I didn’t remove every Layer from front to back to get access because I wanted to avoid dust getting between the layers, so I layed the panel on its front and lifted the backplate (not completely!) to access the backlight.
In conclusion:
I guess the Problem in most cases are the LED Backlight connectors. The solder seems to be corroding or something over the years which eventually will result in a shutdown of the backlight driver. Also, if you consider buying some replacement backlight strips from aliexpress, be aware that most of them are used, not new! You might end up with faulty ones (like I did).
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Follow up: I gave up trying to repair the logic board and ordered a new one. Cost almost 200$ (logic board + shipping + customs) because I live in europe. But it was worth it, the backlight is working fine and the monitor is usable once again. Hadn't used it in almost a year, already forgot what an amazing display it actually has.
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I have been reading these threads the last few days as bought one as broken for 20 quid. I found repeatedly inserting the minidisplay connector and then plugging in the usb kept the screen working for as long as the usb was connected, even if you unplugged and replugged in the disply port however......
I took the monitor apart completely. disconnected all cables and wires removed logic board, power supply and sub woofer and gave everything a really deep clean. Blowing out and toothbrush removing an enormous amount of dust from the fan. Reassembled checking all cable/wire connectors were well seated.
First time reusing took several attempts at plugging in mini display to get it to work, but then.... next time i plugged it in works straight away and at FULL BRIGHTNESS. MUCH better than before!!! I have now unplugged and replugged in mini display 20 or 30 times and it connects every time first time WITHOUT usb connected!! I have also tried every combination, unplugging monitor power while connected to mini display on macbook? Fine. Unplugging mac, then unplugging monitor from power. Turning power back on then connecting to mac? Also fine. Every variation of connection and disconnection. I would thoroughly recommend just giving the unit a thorough clean and checking ALL connections to logic board, power supply, speakers, display, and the two heat sensors. Maybe this won't last long, but maybe it will!
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I would be interested in the long term results, how does the display act these days a couple of months after the try out???
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EDIT Nov. 9 2020: see updates at bottom of post
ORIGINAL POST:
To add to the info found on this problem:
The current fix seems to basically override the overcurrent protection on the monitor. As the backlight strips age, they require more and more current to start up, and eventually the monitor refuses to supply this current, and the backlight stops turning on. One fix is to override this protection, which is not great in the long run and also causes the backlight to be only on full brightness.
To truly fix this issue, one should purchase new backlight strips on ebay or aliexpress. This will cost $10-20. Then, take the panel out of the monitor, and disassemble the panel frame. The LCD panel is attached to the back on the metal frame by ribbon cables. Open it like a book, remove the films and diffusers, and you will have the backlight strips accessible. Replace the backlight strips, rebuild the monitor, and things will work like new. It’s a PIA, but in the end, you will have a working monitor with fresh backlight strips that should last somewhat indefinitely and you will retain brightness control and overcurrent protection.
I have accomplished this repair successfully on an ACD. I have also replaced the backlight strips on a 2011 27” iMac, which is the exact same procedure as the ACD as the panel (LM270WQ1) is shared between them.
EDIT Nov. 9 2020:
Replacing the LED strips did not permanently fix this issue. I think it helped some but frequently the display backlight would flicker before failing to turn on at all. At this point, I replaced the logic board with a known good board. I’ve had no problems since. Unfortunately, I don’t know what exactly went wrong on the logic board.
My theory on why this happens:
Thus, if your monitor is suffering from (1), then fixing (2) by replacing the LED strips will reduce the severity of the monitor’s symptoms. This will be a temporary and incomplete fix because (a) the strips will age and (b) the overcurrent protection kicks in too soon anyway. Instead, replacing the motherboard will be a more robust fix, because the aging LEDs shouldn’t really have much of an impact (27” iMacs use the same panel and I’ve never heard of them having this particular failure) and because it will hopefully be a logic board with properly functioning overcurrent protection.
UPDATED TL;DR: Replace the logic board.
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Hey Michael,
Could you perhaps provide a link where you found the led strips to order? Could you find original replacements, or more likely a LED strip with similar specs?
Thanks,
Robert
This is the one that I bought: https://www.ebay.com/itm/2ps-Original-FO...
Note that the backlight in each monitor is comprised of two discrete strips. So, what is linked above is a set for one monitor. I was a little disappointed in how long it took the seller to ship. Once they shipped, the item arrived very quickly from China.
There are many other sellers selling the same product on Aliexpress.
Be advised that replacing the backlight is an annoying and somewhat difficult procedure.
Super cool, thanks, i ll order one asap. I took my display apart already once and made a lot of photos to this forum, so im aware of the amount of work. Thanks for the heads up, though.
Hello Michael, I wanted to install the strips today, but realised that they are for 27" and mine is 24" display. Then I tried to search all over internet for the 24" strip (one piece instead of two), but I can't find it. Maybe you have an idea? @michaelb12345
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7 Comments
Hi All... just wanted to post that i have had many issues with the backlight failing on my Apple LED Cinema Display 27". While Michael and others on this post have commendable electronics skills, on my display, I have localized the problem to be with the All-In-One Cable. Swapping out power supply and logic boards did nothing to solve my intermittent problem of the backlight going out. But swapping out the cable solved it for me... for a time. My display is 5-years old and I am currently on my fourth All-In-One cable (922-9362). It's a poor design. The cable seems to last for about 12-18 months and then starts going out intermittently without any major event happening. Why someone would combine a USB, Power, and Mini-Display into a single cable is beyond me... except that they can charge $140. for it! Cables are typically reliable and usually be able to be taken for granted. Unfortunately, in this case, I have found it to be anything but. Paras.
tikku tarafından
hi tikku, could you please describe the symptoms of your backlight failure? I just want to check whether my display also needs a new all-in-one cable. thanks very much :)
Jan Wewering tarafından
Hello! I have one question. Is it apple cinema 27" and thunderbolt panel compatibile together?
Thanks for answer. :)
Miran Hadžiahmetović tarafından
I’ve the same problem that OP describes but in my case the screen is black but with some black glow and no trace of any picture when you look closely — what the ACD Technician Guide describes as “no video” rather than “no backlight”. The opposite of most the answers here.
The computer is aware of the monitor and the sound, camera, USB all works — I can even control the brightness of what I assume is the backlight. But the screen is black, usually. But every so often the screen decides it will work and it works perfectly until it goes to sleep or I turn it off. That’s the thing I find weird.
The Guide says to replace the LCD panel.
But I’m dubious, as it feels like a logic problem. A broken LCD panel wouldn’t work occasionally, would it? It feels like a logic board, or maybe PSU, or maybe the octopus cable.
I was hoping the troubleshooting in this thread (by far the best I’ve found on the net) would shed some light on this case but it seems almost everyone was having backlight woes which they solved. Yeah good for you. (Actually the little wire trick sounded so cool I wished it was my backlight.)
I don’t have a second monitor to try swapping out components and figure there must be a better way than buying possible spares. At that point the suggestion to justbuyareplacment.com looks cheaper.
So how else can I tell what’s knackered?
Any armchair detectives? Some more clues below.
I’ve taken it apart and none of the capacitors look bulgy, no loose wires, nothing at all looks suspicious. Not even much dust in there, which is impressive as this is a dusty house and mostly for its 10 years of life it’s been sitting around unused.
There’s not much pattern as to when it works and when it doesn’t. Either it or the computer needs to be off for a while (30 minutes?) for it to stand a chance of working. It feels like unplugging everything for a while gives it a better chance of working, although sometimes it happily works without unplugging, as long as the computer has been off or in standby. The house is always cold, 17C, and the monitor never seems warm so I don’t think it’s temperature.
What I can’t help feeling is relevant is that the black screen first stopped working shortly after I started using it with a non-Mac and a Mini-Displayport to Displayport cable. Maybe I should have mentioned the infidelity sooner but I’ve not seen anyone anywhere talk about this being a factor. I blamed the motherboard in that new computer and the wire and all sorts but ruled them out (a) because even there it works sometimes, (b) I got a couple more cables and had the same problem, and (c) the problem persisted when I plugged it back in to the Macbook even after a {P,NV}RAM reset.
Now it doesn’t matter whether its the Macbook or the non-Mac, once in a while it works, but usually there’s just a black glow. Maybe it works a little more often if plugged in to the Macbook, like 1 in 10 vs 1 in 20 for the non-Mac.
The other breadcrumb for the detectives is that occasionally it comes up at boot with part of the screen showing, like 1/3 across the top, with the rest glowing black.
So could it be a fault in the Displayport wire, sometimes it lines up right and other times it doesn’t and once in a while one specific wire lines up so part of the screen works? I’m not an EE but that seems dubious. A vigorous shake of the wire doesn’t break it when it’s working, and that seems fairly conclusive to me.
The best hypothesis I have is that there’s a jilted lover detector in there that knows I cheated on Mac and decides to wear black most the time but occasionally chooses to remind me how beautiful this display is, what I’m missing out on. Only half joking, the jilted lover detector was probably not designed as such but rather is some electrical component in there that handshakes with the MDP video signal and Macbook’s dulcet tones are optimised for it, and in its old age got a shock when a vulgar non-Mac tried to talk to it. The shock pushed it over the edge and now it has only occasional moments of lucidity.
Does that seem plausible? What component would act like that? Where would it be, and is there a cheap way to get it to back to working order?
Many thanks to any experts still lurking on this thread!
Alex H tarafından
I don't mean any offense to anybody but this is one mess of a thread. Here's some IMO about this situation. The monitors are not worth repairing. 1) All of my customers from CAD operators to graphic designers are happier with a $150 32"1080P HDMI TV monitor. No, the video quality is not as good under a direct comparison but the size makes up for it and there is no eye strain. The adapter for MacBooks is a small additional cost. 2) The direct wiring of the LED circuit is not an acceptable solution to deal with the power supply problem because it stays on and you can't control the brightness, not a solution I could use with any client. 3) The backlighting strip connectors and the jumper connector are a fix I have tried a number of times. It works occasionally but isn't worth the time because the monitors suffer from intelligent cable problems and other issues such that when I fix one, the customer ends up bringing it back, 4) The claimed BIOS calendar timed destruction is something that simply doesn't exist because many of these monitors that see little usage are still working like they did since new. Unfortunately, by the time someone that comes here has had the frustrating experience of trying some of the carefully detailed solutions to no avail,,they will have wasted more time than these old monitors are worth. Unfortunately they simply do not hold up as well as MacBooks.
hedrickja tarafından
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