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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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8th Jun 2022, 1:22 pm | #21 | |
Pentode
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Re: Beocord 5000 (Type 4715) Capstan Motor Speed
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8th Jun 2022, 4:02 pm | #22 | |
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Re: Beocord 5000 (Type 4715) Capstan Motor Speed
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Regards, Jan |
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8th Jun 2022, 4:37 pm | #23 |
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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 |
8th Jun 2022, 6:44 pm | #24 |
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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 |
8th Jun 2022, 6:51 pm | #25 |
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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 |
8th Jun 2022, 8:00 pm | #26 |
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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 |
8th Jun 2022, 9:20 pm | #27 |
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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 |
21st Jun 2022, 11:24 pm | #28 |
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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. |
22nd Jun 2022, 1:08 am | #29 |
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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 |
26th Jun 2022, 8:15 pm | #30 |
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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. |
26th Jun 2022, 9:34 pm | #31 |
Dekatron
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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 |
26th Jun 2022, 11:22 pm | #32 |
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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 |
27th Jun 2022, 9:45 am | #33 |
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Re: Beocord 5000 (Type 4715) Capstan Motor Speed
Spring balances covering various grams/Newtons ranges are available from various places such as Amazon.
David |
27th Jun 2022, 11:18 am | #34 |
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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 |