Apple 27" Cinema Display (A1316) has trouble turning backlight on

[slimmy182]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Do you still want this info? Let me know and I will look. Send me a PM or I will likely not see your post.

Can you please help me figure out this cap value? C308

[howardc64]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

I've fixed about 5-6 of these (27 iMac, Thunderbolt/Cinema Displays) by just resoldering the LED bar connectors. Old lead free solder joint probably weakened from thermal cycling. Here is the write up. See the last few pages for the actual LED bar connector that need solder touch up.

https://drive.google.com/file/d/13Gq...ew?usp=sharing

[avneeshshrotria]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Hey misterkeeks, amazing picture dude... thanks a lot for it ! Exactly what I needed . Now I need to order all of the resistors and figure out the Oscillator pin caps the two white ones in your picture either-side of resistor 93b. If you have any ideas do let me know. But anyway thanks again for the image

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

See attached.

[avneeshshrotria]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Guys I'm still unable to source a picture for the thunderbolt power supply. Would really appreciate if someone could help with images . Thanks

[iuliantv]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

in the link above he also says in that post that, to connect only to 2 ends of some 3v resistors, that the third channel is not used, which is a mistake, because the inverter has 3 channels, 3 bars that go up to about 80v when pwm is forced to a maximum of 3 volts, why do I say that? today I struggled again and I managed to turn on the monitor only if I connected the third contact, I think it had a faulty channel or part of the LEDs to say that it was in error, finally I solved the problem without leaving that change, I had imperfect contacts inside the display, at the connectors of the led strips, I had to undo my eyes, working until about 30 minutes ago

what he was saying

,, 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 on 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 volts.
thank you
https://i.postimg.cc/J7NYnvdY/P-2020...4-v-HDR-On.jpg
https://i.postimg.cc/bNL60bPQ/P-2020...4-v-HDR-On.jpg
https://i.postimg.cc/CxQmXgz5/P-2020...5-v-HDR-On.jpg
https://i.postimg.cc/0yQVVQ5h/P-2020...7-v-HDR-On.jpg
https://i.postimg.cc/HsTZ7zqY/s-l1600.jpg

[iuliantv]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Thanks very much. Yes I'm still stuck with a non working display dude to this power supply issue! Please share images or values as you see fit !

I'm sorry, but my apple display 27 "has a completely different source of power, otherwise I would put pictures with it

[iuliantv]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

hello, I have this apple cinema display 27 "A1316, with well known problem, it has no backlight, I applied the method described in other forums, I minimized the light from the macbook, I restarted the systems, it started ok apple cinema display 27", the light seems to be correct, without shadows, spots or dimly lit parts, which leads me to think that the LEDs, the backlight is ok, I applied the method described on other forums, I removed the 3 resistors, and I applied 3v on the ends of 2 of them, I put on all 3 ends, without result, did anyone find another solution? something needs to be done besides removing the 3 resistors and applying 3v ,? thank you
https://www.ifixit.com/Answers/View/...he+Logic+board

[avneeshshrotria]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Thanks very much. Yes I’m still stuck with a non working display dude to this power supply issue! Please share images or values as you see fit !

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Hey , can someone please help ?

Do you still want this info? Let me know and I will look. Send me a PM or I will likely not see your post.

[avneeshshrotria]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Hey , can someone please help ?

[avneeshshrotria]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

guys I need the values of some of the components around NCP1605 on the power supply board .

I'm attaching an image for reference . I would really appreciate it if someone could help.

Apple thunderbolt display PSU

Board model number : PA-3251-3A


the first one I got the this thread itself.

and the burnt one is what is the current condition of my power supply .

Also if someone is aware of schematics . I could just use that.

thanks everyone. this is one of the best fourms I've come across .

[CapLeaker]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Personally, I’d stick it in my ultrasonic cleaner and after that I’d bake it in the oven for 20 mins. Got nothing much to loose.

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Any thoughts before I spend $30 on a (used) logic board/backlight controller?

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

I spoke too soon regarding the success of this repair. Shortly after replacing the LED strips, the problem persisted.

So,

• Replacing the Power Supply
• Replacing the LED Strips

both have failed to fix the issue, which leaves me with the logic board.



For what it's worth, 27" iMacs use the same panel, but do not fail in the same way. I guest that should suggest that the failure is not located in the panel, but in the logic board (which is not shared with the 27" iMac. Any ideas on how to troubleshoot this?

This problem happens when the backlight controller does not provide a PWM signal to the LED drivers for brightness. Previous "repairs" seem to simply bypass the controller and tie the PWM to 3.3v, thus keeping the backlight on at full brightness.

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Thanks! I'm sure others with the same problem will appreciate this info.

Hopefully. Other people with no backlight found that giving a constant 3.3v to the PWM input on the backlight controller restored the backlight - at full brightness, permanently of course. They seemed to think that the issue lay in a bad microcontroller that failed to produce the signal. Given the success of this repair, I'm inclined to think that the issue was in the overcurrent protection correctly triggering and the failure to generate the PWM signal was merely a symptom of aging backlight.

[jetadm123]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Thanks! I'm sure others with the same problem will appreciate this info.

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Good job on the fix. For future reference, can you please supply the part number or seller you purchased the LED strips from?

This is what I purchased - later on I realized that other sellers on AliExpress had it cheaper - about $11. Attached a picture for posterity.

This is the same panel used in the 27” iMacs- the backlight likes to fail there too, typically the connector on one side goes out, leaving half the display dim.

[jetadm123]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Good job on the fix. For future reference, can you please supply the part number or seller you purchased the LED strips from?

[Misterkeeks]

Re: Apple 27" Cinema Display (A1316) has trouble turning backlight on

Replacing the backlight with new LED strips fixed the issue. So, I'm inclined to say that a lot of the common no backlight failures on this model stem from a failure of the LEDs.

Unfortunately in the process of replacing I must have strained one of the ribbon cables - I now have a line running down the side of the screen.