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Beogram 6006 hums once each platter rotation

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ulrikmm
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ulrikmm posted on Sun, Dec 29 2013 8:38 PM

Hi, 

I am the happy owner of a Beogram 6006 with a nice MMC 4000 cartridge. The turntable has the plastic tachy disc which visually seems intact, and the platter rotation is stable.

However, once per record revolution, a hum reaches the speakers. It sounds like electrical hum, and not as anything is scraping.

Any suggestion as to what causes the problem, and how to solve it? Could it in some way be related to dried out capacitors?

Ulrikmm

 

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Dillen
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Answered (Verified) Dillen replied on Sun, Dec 29 2013 9:13 PM
Verified by ulrikmm

Welcome to Beoworld !

What you have is the typical first symptom of tachodisc breakdown. It will only get worse from now on
and, eventually, the last two digits of the speed readout display will start flashing, indicating that the processor is
not able to keep the speed stabile.
The tolerances of the tachodisc is insane (trust me, I know) and, even if most discs fail with clearly visible deterioration,
you cannot tell if the disc is good by looking at it.
Actually, if you have the printed photographic version it's almost guarateed to be failing by now.
The printed pattern losens from the base material and any offset, visible to humans or not,  will cause a
timing error and a corresponding speed correction from the processor, immediately followed by a braking maneuver since
the platter now rotates too fast.
This is what causes the hum from the eddy-current ("platter motor") coils.
New reproduction tachodiscs are available (from me). They are in stainless steel, they will last practically forever
and they are produced to exact specs, actually measured to produce less jitter than the original steel ones used
by B&O in the last production Beograms.

A capacitor kit is also available for Beogram 6006, 8000 and 8002 (which are all quite similar in these aspects).
Worth grabbing one and replacing the lot while you are at it. If they are still the original caps, they will
need replacing by now.

Martin

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Dillen
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Copenhagen / Denmark
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Answered (Verified) Dillen replied on Sun, Dec 29 2013 9:13 PM
Verified by ulrikmm

Welcome to Beoworld !

What you have is the typical first symptom of tachodisc breakdown. It will only get worse from now on
and, eventually, the last two digits of the speed readout display will start flashing, indicating that the processor is
not able to keep the speed stabile.
The tolerances of the tachodisc is insane (trust me, I know) and, even if most discs fail with clearly visible deterioration,
you cannot tell if the disc is good by looking at it.
Actually, if you have the printed photographic version it's almost guarateed to be failing by now.
The printed pattern losens from the base material and any offset, visible to humans or not,  will cause a
timing error and a corresponding speed correction from the processor, immediately followed by a braking maneuver since
the platter now rotates too fast.
This is what causes the hum from the eddy-current ("platter motor") coils.
New reproduction tachodiscs are available (from me). They are in stainless steel, they will last practically forever
and they are produced to exact specs, actually measured to produce less jitter than the original steel ones used
by B&O in the last production Beograms.

A capacitor kit is also available for Beogram 6006, 8000 and 8002 (which are all quite similar in these aspects).
Worth grabbing one and replacing the lot while you are at it. If they are still the original caps, they will
need replacing by now.

Martin

ulrikmm
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Thanks for your reply. I have started a conversation with you regarding the tachydisc.

BTW, the aluminium piece that surrounds the platter is loose. Would it be OK to glue it with epoxy, or must it be glued with doublesided adhesive tape as it was originally? 

I have chose to glue the aluminium panel above the tonearm with epoxy, as it kept falling off.

Ulrikmm

 

Dillen
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Dillen replied on Mon, Dec 30 2013 8:13 AM

Epoxy will be fine.
Rememer to account for the tiny spring that sits in a hole near the leftmost forward corner.
It connects to the underside of the aluminium surround for static discharge.

Martin

Spassmaker
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Hi all

This is an quiet old discussion but I stumbled today over this.

I had a similar problem with a humming at each relevation of the platter, even with a new lasercutted tachodisc from Dillen.

Today I decided to put a small amount of T 7000 glue underneath the black subplatter ( only at the inner hole and only a small amount) just to fix the subplatter to the spindle.

The glue is usually used for mobilephones to attach the backcover, and you can remove the glue easily with your fingers, peeling it just of.

The humming was gone in seconds.Lets have a Party !!!

There must be a tiny gap between the black subplatter and the spindle with the tachodisc. A little rattling which is audible through the pickup system.

In my opinion there is a constant regulation for the speed and this regulation is always working a little (very little) bit because it´s a dynamic process to keep the platter at a constant speed.

For me it was a solution and I´m happy again to listen to my records without a humming between the tracks ;-))

Stay tuned.

Best regards

Christian

 

ouverture
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Hi Christian,  I think I have a similar issue, but not so much humming, but more of a wiper blade sound

https://www.youtube.com/watch?v=oxh-tJ5opHE

was your hum similar to what I am hearing on my Beogram ?

thank you 

Peter

 

Spassmaker
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North Germany
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Hi Peter

If you start the player as usual and drop the tonearm in the endgroove of the LP there would no music disturb the "humming".

So for me it sounds like the humming from the motor just like I had.

But before more investigations are made, please check the tachodisk for any damages.

Maybe a platterweight would help a little bit, some centerholes of the vinyl are drilled a little too big and when the vinyl is leightweigt and maybe bended a little bit, the humming comes more to hear.

 

Kind regards

Christian

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