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Vintage Tape (Audio), Cassette, Wire and Magnetic Disc Recorders and Players Open-reel tape recorders, cassette recorders, 8-track players etc.

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Old 8th Jun 2022, 1:22 pm   #21
Krolroger
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Quote:
A large high voltage run capacitor would not be needed, maybe a few 63v or 160V MKP or FKP capacitors in parallel? 3 times 4,7u and one 2,2u would make up 16,3u which would be within tolerance if the original was 16u.
Nice idea. Let's see if the big polyprop one fits first.
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Old 8th Jun 2022, 4:02 pm   #22
Jan Zodiac
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

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Originally Posted by Krolroger View Post
Thank you all for your contributions.

I have ordered the film cap which will probably fit if I 3d print an adapter board.

(Back to back elko solution was adopted by Beolover in his 4715 restoration but it may not be optimal as Michael suggests).

https://beolover.blogspot.com/2015/0...ing-power.html

Jan, I've fixed up a couple of Beocenter 4000 (Type 1603) which have an almost identical tape deck, but the motor (looks identical) has a different part number. Though both run off a 30V~ supply and see 18V across them and use a 16uF run cap. I wonder if they are in fact interchangeable.

Interestingly, the motor doesn't seem to lack torque. If I slow down the capstan spindle, TR2 collector voltage goes towards positive which confirms that the servo is functioning.

Simon
I think the motor from Beocenter 4000 is electrically identical to the one from BC5000. Maybe it has another pulley, which would give it another part number. I am not sure about this, I am guessing only. I brought a BC5000 back home today. Not a type 4715 but a 4705. I believe the motor + servo is the exact same. I will open it later and check out voltages etc.

Regards,

Jan
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Old 8th Jun 2022, 4:37 pm   #23
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

So, I just checked the DC resistance of the motor coil. They each measure 100R (blue-yellow, red-yellow), and then 200R between blue-red.
Powering it up will need some time. It is filled to the brim with horrible ROE electrolytic caps, as well as tantalum electrolytics. I will of course focus on the motor servo board, which has at least one fried, once red, ROE capacitor.

Jan
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Old 8th Jun 2022, 6:44 pm   #24
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Hi Jan and all,

The new run cap does fit.

My motor coil measurements are 97R/99R and 196R measured in circuit.

But I'm still getting -0.6V at TR2 collector in Play.

Simon
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Old 8th Jun 2022, 6:51 pm   #25
Jan Zodiac
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Hi Simon,

Well I didn't suspect the run cap in the first place, as I know a lot of these motors were replaced because they went bad. I still suspect the copper rods in the rotor. I will try to power up the one I have, and see what it does.

Jan
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Old 8th Jun 2022, 8:00 pm   #26
Jan Zodiac
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

So, I did some measuring. First of all, what a HORRIBLE mess of a tape deck!!! Jeez... Alone fitting a new belt is terrible.
Anyway, I got another belt fitted, and replaced the bad 1uF cap on TR2's collector.
As can be seen in one of the pictures, on idle the voltage on the collector of TR2 is just above 10V as stated in the schematic. In playback mode it sinks to between 7 and 8V which I would say is fully okay. Especially given the fact that this deck was never restored. On playback I had to push the head/pinchroller assembly towards the cassette by hand, because the solenoid somehow did not pull. On fast forward/rewind it pulls halfway though, which I guess is normal. So this deck has some issues. After all, it is a Bang & Olufsen...
When playing a cassette and pushing the heads into the cassette by hand, the tape speed is correct though, so the motor servo and motor is working 100% as it should. I was a bit impressed by a nice and clear sound, even as unrestored.
This type has 3 heads by the way.

I don't think this will help you further with your BC5000, but I am pretty sure the motor in your deck is defective.

Oh, another thing, I tried shorting C-E on TR2 and then it certainly ran way too fast.

If you need any of the parts from this one, you can have all you need FOC, except shipping of course
I am not keeping any of it, since this is not at all my field.

Regards,

Jan
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Old 8th Jun 2022, 9:20 pm   #27
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Hi Jan,

I'm impressed that you managed to get a new belt on so quickly!

Brilliant offer, thanks. I will PM you.

Simon
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Old 21st Jun 2022, 11:24 pm   #28
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Big thanks to Jan, whose parcel from Denmark containing assorted Beocord 5000 bits arrived today.

I swapped the capstan motor and I was sure that my problem would be solved when I discovered a solder splash on the field winding of the old motor thinking that shorted turns might have caused erratic functioning.

But with the new motor installed, the too positive PLAY voltage at the collector of TR2 is still evident. I'm seeing -13VDC in STOP increasing to -1.3 ish in PLAY suggesting that TR2 is working too hard to sink enough motor current. It's certainly getting warm.

I am sure that the servo circuitry works correctly.

So I now think that Michael might have been on the right lines and that either the motor is having to work too hard to overcome pinch roller pressure or that the take up moment is off.

Mechanical adjustments (and there are many of them described in the manual) require factory tools.

I will see if I can achieve anything with a bit of gentle adjustment starting with the rollers.
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Old 22nd Jun 2022, 1:08 am   #29
Jan Zodiac
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

I'm happy it arrived.
What if you remove the belt and let it spin unloaded and then check the voltage across TR2? I don't think the pinch rollers will be able to put so much load on the motor, that the servo will not be able to keep the correct speed. Unless something else is forcing it to slow down, like bearings etc.

Jan
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Old 26th Jun 2022, 8:15 pm   #30
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

The problem from the outset was excessive pinch roller pressure. Backing off the spring that acts on the roller arms in Play has reduced the load on the motor to the extent that the collector voltage on TR2 is now in the right ball park.

Has anybody any advice on how to get the pinch roller pressure optimal (other than electrical load measurements)? The manual refers to a proprietary spring balance reading of 400 p which is not a unit of measurement I'm familiar with. (Page from manual attached).

My thanks to all who contributed.
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Old 26th Jun 2022, 9:34 pm   #31
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

It quite possibly is Ponds.

See Posts 15 - 23 in this linked Thread -

https://www.vintage-radio.net/forum/...d.php?t=162605

Some confusing/misleading info during those posts (by me) but Post 23 sums it up accurately.

David
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Old 26th Jun 2022, 11:22 pm   #32
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

David,

Thanks.

If 400 p equals 400 grams of force, a tin of soup, some cord and a pulley should be a reasonable indicator of thrust roller pressure absent a spring balance.

Simon
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Old 27th Jun 2022, 9:45 am   #33
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Spring balances covering various grams/Newtons ranges are available from various places such as Amazon.

David
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Old 27th Jun 2022, 11:18 am   #34
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Default Re: Beocord 5000 (Type 4715) Capstan Motor Speed

Thanks, David

Now ordered. Some Molykote DX as well which will free things up a bit.

Simon
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