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Latest post 02-21-2012 9:36 AM by viive. 12 replies.
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  • 02-08-2012 5:14 AM

    • viive
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    Beocenter 7700 turns off randomly

    Hello!

    I recently bought a Beocenter 7700 and I love the device! Everything is working with it and it sounds great, but when I play records or a cassette beocenter sometimes turns off randomly. Sometimes it plays the whole record  but recently it has been turning off more often in the middle of the record. With tuner it hasn't done that. A friend of mine suggested that it might be an issue with old caps. Any thoughts?

    Juho

  • 02-09-2012 1:42 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    I noticed that there is also an audible quiet humm from my 7700 whenever its power cord is plugged in the wall socket, even when the power is switched off. Could this indicate that there is something wrong with the power supply?

    Every time beocenter turns itself off it does that in a controlled way: it raises the tonarm and turns it away from the platter. After that the power is turned off. Is there a safety mechanism in beocenter 7700 if it loses power, or does that mean that the microcontroller gets an signal to turn the unit off?

    Has this happened to anyone else?

    Juho

  • 02-09-2012 5:24 AM In reply to

    Re: Beocenter 7700 turns off randomly

    Is the problem occuring at a certain time each day?

  • 02-09-2012 5:52 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    Good point... I haven't touched the timers at all yet, but i can check them tonight. Last tuesday my 7700 turned off five or six times while playing, so I'd suspect it's not the timer...

    Juho 

  • 02-09-2012 6:26 AM In reply to

    Re: Beocenter 7700 turns off randomly

    The transformers in many B&O kit of this age hum even in standby. The AC selector has probably been switched to 220V since new. Nowadays, this means it is running at a slight overvoltage, and switching it to 240V might diminish the hum a bit (unplug before touching the dial!). Other causes may be dried out rubber bushings at the transformer mountings.

    I'm not familiar with this model so I don't know how the fault switch at the amp operates (whether it drops dead at once, or does the turntable still turn off normally), but another reason for dropping to standby can be incorrect idle current setting of the power amps, due to bad trimmers. This would also show as abnormal heating of the amps, but it's of course hard to say what's abnormal if you've never seen one of these before...

    Another cause for erratic operation is then the old dried out capacitors and/or bad solders. Bad caps at the power supply can cause some of the hum as well.

    -mika

  • 02-09-2012 6:50 AM In reply to

    Re: Beocenter 7700 turns off randomly

    When I restored my Beocenter last year i found about 5 or 6 leaky caps scattered throughout the system and I did replace the idle current trimmers they had drifted away from the original setpoint.

    It is a great set. I am listening to it right now.

    Cant remember - not sure if the 7700 had an overload sensor installed that would cut power or not.

  • 02-09-2012 9:20 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    Ok, I guess recapping would do good, even if it wasn't a leaking capacitor causing it to turn off. And replacing the old trimmers at the same time might be a good idea.

    I have done some soldering before: battery powered small amps and guitar effects as a hobby, but I haven't worked with high voltage devices before...   Is there lethal voltages inside the beocenter caps? Any ideas where I should get new caps?

    Juho

  • 02-09-2012 11:39 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    The humming stopped when I turned to 240 volts. I noticed that beocenter turns off even while playing radio if I turn the volume up high enough...

  • 02-09-2012 1:14 PM In reply to

    Re: Beocenter 7700 turns off randomly

    Might be a problem with the no load potentiometers in the amplifier. Is the amplifier getting hot? If not, take the batteries from the remote and see if the problem still occurs.

  • 02-10-2012 1:16 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    It isn't the remote control, that's one of the first things I thought and tested. I opened the beocenter and tested the no load current. It was 36 mV in TP200-201 and 40 mV in TP100-101. (...yes, I found the service manual...) I adjusted the trimmers so that the no load current was 10 mV and after that I was able turn up the volume without beocenter switching to stanby. This is very encouraging, but I need to do some more testing when I get the TT up and running again. I'm going to be away for the weekend so that'll have to wait 'till next week. (Can't wait...)

    Juho

  • 02-10-2012 4:05 AM In reply to

    Re: Beocenter 7700 turns off randomly

    viive:
    It was 36 mV in TP200-201 and 40 mV in TP100-101.

    That should be far enough off to cause problems, I believe it will work normally now after adjustments. Those trimmers didn't move by themselves though, so they are bad - replace them, or the setting might not stay for long.

    If it works and sounds good after that, no rush with the capacitors - but take at least a visual look. If any are obviously leaking or cracked, better replace them before they cause problems.

    -mika

  • 02-10-2012 4:53 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    tournedos:

    That should be far enough off to cause problems, I believe it will work normally now after adjustments. Those trimmers didn't move by themselves though, so they are bad - replace them, or the setting might not stay for long.

    Will do.

    I didn't see any visual damage in the capasitors, and there is nothing to complain soundwise. So I guess I'm content with the caps as it is for now.

    Juho

     

  • 02-21-2012 9:36 AM In reply to

    • viive
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    Re: Beocenter 7700 turns off randomly

    I've been listening to my beocenter for over a week now (with sonab od-11 speakers, which I bought last week). I've also used quite high volymes, trying to provoke the fault switch, but Beocenter hasn't turned off. Thanks for your help!

    There are stil some minor issues I need to fix: the plastic part of the turntable lid came off, the hinges are quite stiff, and I've now got a small background noise, probably the grounding problem with one of the tape screws, which is mentioned in some other posts in this forum...

    Juho

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