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Lennart25
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Lennart25 posted on Fri, Apr 3 2020 8:32 AM

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Daniel
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Daniel replied on Fri, Apr 3 2020 11:00 AM
Hi, I had problems with a high pitch noise several years ago. I believe it ended up with B&O replacing the CD-unit. Can’t remember if it still was under warranty at that time. The technician sad it’s a problem with “the open air-design”, normally the mechanism is in a closed space isolating such noise.

The replacement worked and no noise since then.
matador43
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I 'd be curious to see the answers as I have that noise too.

I've bought a faulty BS9000 and have changed the laser by myself, so i've assume the noise was from a cheap quality part.
I also be unable to tell if that sound was present before as the unit was not working.

Well, not it is but it is also close to my desktop and in quiet music I can hear it. Would be nice to find a fix if there is!

Frank Elton Jensen
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I am a retired Radiomechanic and Electronics Engineer. Started recently to do some restoration and i havent really accuired much experience yet since i left the Audio buisness in my early twenties . I am now 55 . However nice to be back to my former education . 

Doing a restoration on a cdx2 i came across a high pitch sound . this was a mechanical issue and could be clearly heard at zero volume. Only when the CD was playing , in pause it was not there even though CD still spinning. Rootcause seemed to be a resonance phenomena caused by the tracking/focus coils exiting the swingarm system and especially the metal bracket holding the swingarm assembly together. At least damping the metal clamp with some foam made a difference. Dont recall what made the biggest difference because it finally went completely away after a dismantling , lubricating and realigning of the swingarm. 

At the time i had this failure i found reports on other brands having similiar issues and it seemed to related to mechanical exitation/resonence of the mentioned coils. I believe some Sonys had issues like this. 

I dont know the beocenters yet so i dont know if it is a swingarm CD version or the newer CDM12 or if this phenomena may exist in either version. 

I hope this info may be of use.

Regards , Frank

matador43
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Hi and welcome to Beoworld Frank Elton Jensen,

This is very interesting and at the same time a little bit dark. Could you please be more specific about that :

Frank Elton Jensen:
At least damping the metal clamp with some foam made a difference.

Please feel free to ask if you need any details about the cd mechanism in the BS9000 (mine is MK2's 9000 VAM1205).

Thanks a lot.

- - - Edit - - -

Just did the test and the hi pitch noise is there even when paused. Sad

Frank Elton Jensen
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Do you hear it in the speakers and thus controlled by volume setting or do you hear it with volume at 0 ?

I am not sure if it is related but in one of the treads regarding the famous c2103 capacitor it was mentioned by someone that replacing with a non philips cap could cause some high pitch sound dependant on Laser current setting. 

A lot has ben said about this capacitor but no one really investigated this to the end. Fact is that capacitor is nothing special. I have been meaning to investigate this further when i had a unit showing failure related to this cap. From my engineering experience and looking at the laser driving circuitry and the driferent versions i have seen in the schematics i am pretty sure the Philips Engineers has had their trouble getting the Laser emitterfollower driver stable. Emitter followers are proned to oscillations and said to be just a small inductor away from oscillation. I just resolved the same issue in a Power Audio amplifier i am building and my own design. 

So the reason the blue Philips cap seem to be a must is most likely a coincidence that its caracteristics and losses when new in combination with all the stray component values around the emitterfollower mostly jut is enough to keep the curcuitry marginally stable. As components age including the transistor this stability is lost and spurious oscillations occur and even intermittently dependant on temperature etc.

I believe the Laser is still powered in the pause mode since cd is still spinning and ready to continue so just maybe there could be a connection but this is a wild guess and i dont know if this can show up to be heard either mechanically or in the audio chain.

The metal bracket and the foam was just an attempt to see if the mechanical resonant i heard was related to the swing arm assembly . It is not easy safely to poke around the cd drive when everything is running at least i dont do that.

Well i dont know if this helps in any way ?

Frank Elton Jensen
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Well just came to my mind i may recall wrong about the pause mode its some time since. Does the focus and tracking coils operate in pause ? Even though the swingarm servo stops does the focus and tracking still operate i guess so in order to continue quickly and a CD is always unperfect and requires tracking/focus even though the swingarm has stopped at a specific position . since my hearing is bad i have trouble hearing anything above 2khz. I believe i could measure in fact app. 2khz signals in the tracking signals and they would exitate the tracking coils which could then spread mechanically.

matador43
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Thank you for the comprehensive answer.

It helps enough in that I understood its not an easy fix, at least for me. Difficult enough for me to keep it like that for now.

But that is definitely a lead to investigate. 

Just to answer your first question: yes it's definitely coming from the sledge and not from the speakers (heard at vol. 0 or muted).

Again thank you for your input.

 

Frank Elton Jensen
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You are welcome and yes it must then be mechanical related and likely to the tracking coils exiting the mechanics that swings along. 

I hope you can fix it . Careful if you disassemble the swing arm it is not easy to realign.

It gave me a LOT of work. I ended up building my own alignment tool. What was available on the internet just did not work for me and some descriptions on how to use the shadow cast on the laser metal frame i believe is in error and does not work . A shadow cast form a light source vertically above a marker line on a transparent CD will always lie exactly below the marker line regardless of the tilt of the laser pickup. And a shadow is not reflected after all a shadow is lack of light. What is reflected is the neighboring light rays. The original tool used by Philips also speaks of 4mm margin and in my mind this is huge given the distance between the laser and the CD so the original tool with a mirror must do som optic trick to ease the alignment.

However i believe i found another and much easier way and will share off course if anyone is interested. 

If i could just figure out how to attach pictures hmm.

regards Frank.

 

matador43
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For single picture you can go to the "option tab" in the message composer window.

For multiples pics, you should upload them in your media library (in your forum profile) and then , add them to your message by clicking in the media link icon in the composer (the green film strip).

At least this how I do.

 

Frank Elton Jensen
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Well both options causes a message from the system with several causes to why this message occurs ranging from Hacker attempt to system backup in progress .

Beobuddy
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Frank Elton Jensen:

Careful if you disassemble the swing arm it is not easy to realign.

 

The BS9000 doesn't have the swing arm your CDM4 has. The lenses, at the newer mechanisms, which are also driven by coils aren't made to be removed, or taken apart. These newer units haven't the special Philips capacitor.

 

Frank Elton Jensen
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Just realized your issue is on a beosound 9000 and not a beocenter 9000 . Sorry , however the issue is likely the same you just do not have a swingarm CD transport , my mistake Whistle

matador43
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Beobuddy:

Frank Elton Jensen:

Careful if you disassemble the swing arm it is not easy to realign.

The BS9000 doesn't have the swing arm your CDM4 has. The lenses, at the newer mechanisms, which are also driven by coils aren't made to be removed, or taken apart. These newer units haven't the special Philips capacitor.

Big Smile

Maybe pics would have indeed helped!

Anyway… BeoSOUND (6 cd) is still whistling!

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