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Beogram 4002 tonearm always lowers at 12"

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jozo
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jozo posted on Wed, Oct 31 2012 11:35 AM

I have a Beogram 4002 that works perfect except for the fact that the tonearm always lowers at the beginning of the turning platter, even when no record is present. This is fine for 12" records but when playing 7" or 10" records I always have to manually direct the tonearm to the right position and also adjust the speed for 45rpm records. I haven't found any posts of someone with a similar problem so therefore I'm asking for help myself.

I'm thinking of a replacement of the photodiode in the detector arm,  but first would like to know if this will solve my problem.

Thanks,

Job

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Dillen
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Dillen replied on Wed, Oct 31 2012 12:36 PM

Welcome to Beoworld !

There's no photodiode. It is a filament lamp and a voltaic cell.
I suggest you check the lamp first. Does it light up ?
If not, replace the lamp.
If it does, check its position in relation to the lens system. It should have its filament centered right above
the lens and sit as close to the lens as possible.

Still no luck, you need to put a scope to the sensor output and follow the signal through the filtering etc. to see where
in the electronics it is lost.
The radial streaks of the platter gives a nice pulse train for reference.

Martin

jozo
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jozo replied on Wed, Oct 31 2012 1:29 PM

Thanks for your reply Martin!

The lamp does light up so I'll have to see what the inside of the detector arm looks like.

Could you tell me how to take the inside of the detector arm out without the risk of damaging anything. I have carried out some repairs on the Beogram but never had to do anything with the detector arm.

Hopefully I won't have to check the electronic circuit because that will be too much effort.

Job

Dillen
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Dillen replied on Wed, Oct 31 2012 3:03 PM

The whole arm insert with lamp, lenses etc. pulls straight out from the arm housing.
The leads are not very long though, just long enough to get it out and rotate a bit so do be careful.

Martin

jozo
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jozo replied on Thu, Nov 1 2012 7:36 PM

Thanks a lot Martin!

The lamp was a bit out of position, but one of the legs of the lamp was too short so I had to unsolder and solder it again to gain some length.

Eventually everything is in its right place and the turntable works like a charm.

Thanks again :)

Job

Dillen
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Wonderful !
Don't be a stranger now.  Smile

Martin

Søren Mexico
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jozo:
Eventually everything is in its right place and the turntable works like a charm.

Thank you for posting the result, it will help others with the same problem

Collecting Vintage B&O is not a hobby, its a lifestyle.

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