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Beocenter 9500 no sound from Phono Input

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Motorman
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Motorman posted on Sun, Jan 17 2021 11:13 AM

Hi,

yesterday I got the retiped stylus for my Beogram 1202.

I plugged it into one of my Beocenters 9500 and was terribly disappointed as I heard nothing.

It then turned out, after I connected the turntable to my other Beocenter and it worked perfectly there, that apparently the phono input on the first Beocenter is defective.

So I probably have a defect on board 53.

Does anyone have experience which components I should check or replace first?

I am grateful for any tip!

Kind regards,

Wolfgang

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Orava
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Answered (Verified) Orava replied on Mon, Jan 18 2021 2:11 PM
Verified by Motorman

Menahem Yachad:

Here's what your PCB53 should like like after the repair - of course, resoldering all the joints is a necessity.

I had C2, black one on right side of board shorted, no sound. After change that everything was ok.

 blah-blah and photographs as needed

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Menahem Yachad
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Here's what your PCB53 should like like after the repair - of course, resoldering all the joints is a necessity.


Dillen
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Dillen replied on Mon, Jan 18 2021 9:03 AM

Since both channels seems to be missing, it must be something common; 

Check for power supply voltages.
+/-12v across C4 and C5 respectively
26V to the RIAA
Check solder joints at connectors
etc.

No luck? - Put a scope to one of the signal paths and see where the signal is lost.
A dead source selector IC wouldn't be a first.

Martin

Spassmaker
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Hi Wolgang

Is there sound from the other inputs, TAPE 2, AUX, CD, RADIO? If so, I go with Martin, check voltages, connectors and solder joints.

But you can't hear anything on left and right?

I've a quiet similar problem I'm working on in the moment.

On my Beocenter 9500 the poweramplifier is muted so I have to crank up the volume very very high to hear some music from the passive speakers.

If I pull IC 2 PIN 7 (PCB 60) to GND the volume comes back as expected on both channels. So today afternoon I will exchange the IC 2 and will see what happens.

 

It could be a similar problem  with your BC 9500 that the IC 2 on the amplifier board (PCB 60) is defective.

This IC manages all muting circurits of the Beocenter.

In your case IC 2 PIN 5 is interesting, if I'm not wrong, this PIN 5 should be at high level, so TR 21 (PNP) is off, minus 12 Volt on AF MUTE line, TR 403 (NPN) on PCB 53 is off and the input of IC 2  PCB 53 is on, so you should hear the all inputs incl. CD, RADIO, TAPE 1.

If all inputs are OK the IC 1 program select (PCB 53)  could be defective on the Phono Input, seems a little bit impossible that both channels fail but .....no one knows.

Let us know how  far you get with it.

Best regards and good luck.

Christian

 

 

 

Motorman
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Hi,

Thanks for all the answers! Smile

All other Inputs Aux, CD, Tape 1 and Radio are working fine. Only Tape 2 I havn't checked yet so I don't know if this one works.

Only Phone is silent on both channels.

I will start the investigation tonight and report on the results.

Kind regards,

Wolfgang

 

Orava
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Answered (Verified) Orava replied on Mon, Jan 18 2021 2:11 PM
Verified by Motorman

Menahem Yachad:

Here's what your PCB53 should like like after the repair - of course, resoldering all the joints is a necessity.

I had C2, black one on right side of board shorted, no sound. After change that everything was ok.

 blah-blah and photographs as needed

Spassmaker
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HiI'm Happy again.

A new IC did the trick, all inputs  working at full volume.

 

Motorman
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Orava:

I had C2, black one on right side of board shorted, no sound. After change that everything was ok.

Hi Orava,

your tip hit the mark! C2 was short!.

Unfortunately I had no new one at my hands.
So I exchanged it with a very old Philips one I found in the electronic experimenting Box from my youth.
It is probably older then the original one, but I messured it OK so I tried it.

It worked! The Phono input is now working like a Dream.Big Smile

Thanks to all for the contributions in this thread!
For me as an mechanical engineer your help is worth a fortune.

So the humming noise of the transformer is only open functional issue on this unit.

By accident, does anybody know how to polish silght scratch marks from the alluminium mirror surfaces?

Kind regards,

Wolfgang

 

 

Spassmaker
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Well done, congrats!

The mirror finished surfaces are hard to polish without making it worse, try a magic eraser sponge and a light soap, do not rubb on  the mirror it will leave marks and dull spots.

Leave it as it is and don't look always to the scratches, just enjoy listening some cool music. Have a look in the Web for some better looking  panels, but look twice at the offers, If the pictures are from bad quality ask the seller for better ones or leave them and wait longer.

Best Regards and stay healthy

Christian

Motorman
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Spassmaker:

Well done, congrats!

Thank you very much Christian, also congratulations to your successful repair!

You are right, that the sound is much more improtent then the look.

But as we say in Germany: Das Auge isst mit!

I now want to fix the tape screaming noise of my 1st Beocenter, and maybe if I get me to it, I then want to sell the 2nd one on.
I would prefer to do this without scratches.

I think I have now also found the reason for the humming noise of the transformer. The bushing which should isolate the transfomer to the fix screws look very bad and are not elastic any more. See pictures below.

Does anybody know a good substitude for these?

Kind regards,

Wolfgang

 

 

 

Spassmaker
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These are looking mit too Bad, only a few Marks AS it seems.

I'm not a friend or familar with the seller...

https://www.ebay.de/itm/Bang-Olufsen-Beocenter-8000-8500-9000-9300-9500-Panelen-Panneau-Gebraucht-/233865577337?_trksid=p2349624.m46890.l49292

The rubber parts are hard to get, you have to improve something there or search the Web for Dämpfergummis look for pictures, a lot of possibilities.

Best Regards Christian

 

Spassmaker
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Double againšŸ˜£

 

Motorman
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Spassmaker:

 

The rubber parts are hard to get, you have to improve something there or search the Web for Dämpfergummis look for pictures, a lot of possibilities.

 

Hi Christian,

with the help of Martin (Dillen) I found out that these Bushings work for the Beocenter 9500 too:

https://www.beoparts-shop.com/product/transformer-bushings-beomaster-3500-4500-5000-5500-6000-6500-7000-etc/

As you see he has now updated the information in the webshop.

I can really recommend them as usal with Martins parts they fit perfectly.

Kind regards,

Wolfgang

P.S.: I got in contact with the seller of  the Mirror Panels and he confessed that they also had deeper scratches. For this the price was to high.
But thanks for the hint!

 

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