Buzzing PSU - Apple LED Cinema Display 27" (2010)

[Jakob Möller]

Hello!

My first post here.

I have a problem with my Apple LED Cinema Display 27" from 2010. A while back it started buzzing quite loudly and I could not understand why. At first I thought it was the speakers but after speaking to some electronics enthusiasts on a swedish electronics forum we could conclude that it was the power supply unit that was making the sound.

They suggested that I should replace the capacitors on the psu because those are often the problem. I got the psu out of the screen and I gave it to a local tv repair man who replaced all the capacitors. I put the psu back into the screen and it was fine again! I was very glad!

BUT, about a week after this the buzzing started to come back again. At first very softly but now it is quite loud again. Somehow these capacitors where now broken again.

The buzzing gets worse when I have used the screen for a couple of hours and especially if I have the mag safe (power cord from the screen to my mac book pro) connected. The higher the brightness setting the louder the buzz.

Here is a video of the buzzing sound:

Here are pics of the PSU before the capacitors were replaced.

https://imgur.com/a/2zxdJ#3

I managed to hear that the buzzing is the loudest from the two orange components on these pictures:

https://imgur.com/a/2zxdJ#9

https://imgur.com/a/2zxdJ#19

The three big black capacitors laying down on the card were not replaced:

https://imgur.com/a/2zxdJ#10

I really do not know what to do now and my friends on the swedish forum are unsure also. I would really like to fix it somehow.

Does anyone here have any ideas? I would be very grateful for any help!

Thank you!

//Jakob

 

[rumpfy]

Buzzing is usually due to mechanical vibration. In particular, buzzing is often due to the transformers core/cores vibrating. To stop this, the manufacturer uses a glue to damp/join the two separate parts of the core. I would be looking around the transformers to see if anything is wrong there.
if this is the problem, then fixing it by adding more glue may not work out too well. Maybe a tightening of a screw or something will help.
Sorry to be so vague, but I can tell you that buzzing noises is the bane of a device manufacturers life. thats why most transformers/coils I have seen are glued during assembly.

 

[Jakob Möller]

Hello!

Thank you for your reply. I see. I might open it up and poke it with a stick or something then.

But why is it that the buzzing stopped for about a week when the capacitors where replaced and then started again? How do these components effect each other and how can I make them get along? Would it help to replace the transformers maybe?

 

[rumpfy]

I cannot really give you an exact answer.
Replacing the caps may have stopped the noise BUT; were the caps responsible for the noise ?, or was it, that the physical work on the chassis resulted in the noise producing conditions changing enough to not make a noise. It only takes a small change in the location of some parts to move things enough to stop the noise. I believe that if the caps were faulty then it is most unlikely that they have 'failed' again in such a short time.
Just poke around the chassis (with the power turned OFF) to see what you can find. Loose screw, loose metal part.
hope this helps.

 

[Jakob Möller]

Hello again!

Last week I opened up the screen took the PSU out and glued the copper transformers. I put the glue over and around the transformers and let it set. I then put the screen back together and started it up. It was silent. For three days. Now it has started again and it is as bad as before.

Now I and stuck again and I would really appreciate further advice. Should I have the transformers replaced with new ones? Should I just replace the whole PSU? Any other tips/thoughts?

Thank you!

 

[Jakob Möller]

Hello again again!

I got tired of this problem so last week I got a new PSU-card and popped it in there. So far, everything works FINE! And I am so happy I am dancing on tables everywhere I go. It is silent and it is bright and beautiful.

NOW, this doesn't mean that it is guaranteed to stay that way but I am crossing my fingers. I still do not know what went wrong with the first PSU.

Hope this helps others with this problem.

Thanks, Jakob