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

Discussion in 'Troubleshooting and Repair' started by MRenthusiast, Apr 22, 2014.

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  1. MRenthusiast

    MRenthusiast

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    Apr 22, 2014
    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.

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

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

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

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

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

    http://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
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    Get some hot melt glue and stick the inductors (the orangy coloured coils of wire) to the board.

    Don't use too much, because it may cause them to overheat. Eventually the vibration will break the leads or the solder joints. They really should be firmly held in place. Often they have cable ties around them to hold them tot he board, but I can't advise you to start drilling holes in the board.
     
  3. MRenthusiast

    MRenthusiast

    7
    0
    Apr 22, 2014
    Hey Steve!

    Thanks so much for the advice. I will try this and hope for the best!

    I hope you do not mind me asking: do you have a theory of how come the buzzing stopped when I replaced the capacitors? And why it slowly started again after while? It bugs me when I do not understand how things work. :) I would be very grateful if you would explain this.

    Thank you!
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    Maybe when the board was worked on the inductors moved into a position where any vibration wasn't audible. Maybe there's some glue under them that they were briefly re-adhered to.

    It's hard to say.

    It's also possible that the replacement capacitors were poor and that the failure *is* actually something to do with them. But trying the simple things first is generally a good start.

    Note that it may actually make the buzzing louder if the inductors now vibrate the whole board. If so, then I'd start looking for a reason for the device drawing more current than it should. As you've noted, higher power requirements lead to louder buzzing.
     
  5. MRenthusiast

    MRenthusiast

    7
    0
    Apr 22, 2014
    Hmm, the world of electronics is a mysterious one I reckon.

    I will try and learn more about glueing coils and then give that a try and we will see what happens!

    Thank you very much for your input. You have no idea how much this issue bugs me.

    I will post back shortly! Peace!
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    There are better things to use than hot melt glue. However beware that if you decide to use some form of silicone sealant that you select one that is neutral cure or you will be exposing the electronics to acid -- and that's not a good thing.

    Whilst hot-melt glue has the potential to fail, if it has something to bite onto, it should hold pretty well.
     
  7. MRenthusiast

    MRenthusiast

    7
    0
    Apr 22, 2014
    Ok!

    A question: is "coil whine" my problem? I listened to some videos of coil whine and I do not recognise the sound. Or can coil whine sound differently from case to case?
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    The sound an inductor can produce varies from clicks to buzzes to high pitch squeals. The sound is then modified by the resonance that may happen in the case etc.

    About the only thing you're unlikely to hear is a low moaning sound.

    Looking at the photos, there is some white goo on the board. This is designed to stop vibration. If capacitors were replaced then this has either been re-applied or... something.

    One quick thing you can do is to get a large eraser and push it against the components while the power is on an the noise is being produced. WARNING there are dangerous voltages. The aim is to see if you can affect the sound by damping vibrations from a particular component. You might be tempted to use a pencil with an eraser on the end (DON'T), but the graphite *could* be conductive and these pencils have metal holding the eraser. Don't try any of this unless you have easy and safe access and are familiar with mains voltages.

    It does look like only one of the inductors has the white goo on it anyway. Maybe it's the other one.
     
  9. MRenthusiast

    MRenthusiast

    7
    0
    Apr 22, 2014
    I will definitely try this! First I will get a good nights sleep here in stockholm but tomorrow I will open the screen up again and poke around. I will post here with the results.

    Thank you again for your help. It is greatly appreciated!
     
  10. MRenthusiast

    MRenthusiast

    7
    0
    Apr 22, 2014
    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!
     
  11. MRenthusiast

    MRenthusiast

    7
    0
    Apr 22, 2014
    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
     
  12. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,411
    2,779
    Jan 21, 2010
    The problem was clearly mechanical in nature. A new PSU card was probably the best option (getting the transformers may have been a difficult and expensive proposition unless they were stock items -- and this is very unlikely in a SMPS).

    I hope that the replacement doesn't start to suffer the same problem.

    If you were sure it wasn't a multi-layer board, you can drill holes in strategic places to allow you to hold the toroids and transformers in place with cable ties. The obvious downside of this is that if you're not careful you can drill through a trace and stop the PSU working. On multi-layer boards this is almost impossible to avoid unless you know for certain what the inner layers look like.
     
  13. macuser

    macuser

    1
    0
    Dec 15, 2017
    I realise this is an old post - but it came up when I was trying to sort out the buzz in my old 27" display.

    I tried changing the capacitors but the noise continued. I replaced the power supply board with another one (another LiteON) and there was different sort of noise from it (after running the display while open with power supply inverted I figured its the inductors (toroids) on the second board.

    I have now replaced the power supply with a flextronics board (looks newer and better made that the Lite-on board).
    No more buzz or hiss.

    I wonder if Apple might have changed supplier from Lite-on to Flextronics to address an issue with the design or manufacture of the power supply? don't know. Either way it looks like I'll get a bit more life out of the old display yet.
     
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