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Bang & Olufsen Beogram 4002 Turntable 3 Volt DC Motor Speed Not Constant

Discussion in 'Troubleshooting and Repair' started by jfrancis, Feb 25, 2011.

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  1. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello All,

    New here but have a problem that I could use help with. I have a Beogram turntable I have restored that was made in the mid seventies. I have a problem with the servo controlled 3 Volt DC motor that drives the belt for the platter is not running at a constant speed. I know it is the motor because I have put in what I know is a good motor from another table and it works fine. But I need two good motors one for each of these tables. The history is that the bushing for the motor shaft was dislodged when I got the table and took it apart to get it back in place. I cleaned and lubricated the motor before re-assembling. The motor will run at the correct speed for up to 45 minutes and then slow down or warble. Sometimes this happens when the motor is not that warmed up. I have taken the motor apart several times to see what might be the problem but no luck. It has a capacitor that I have ordered a replacement for but a friend who knows a little about motors says he thinks that would not be the fix. The armature has two 1/6th inch brass colored strips that are split horizontally to the pole where they make contact that I assume would be called the brushes. They are easily bent when reassembling the motor but appear to be straight and making contact with the metal of the pole of the armature. They have a microsopic space separating them. I am a real novice so if you have comments be prepared for that. ;) I have contacted the Forum for Bang and Olufsen enthusiasts but no one has been able to help.

    Regards,

    John
     
  2. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    Hello jfrancis

    I have just googled to get some information about the same problem you have and was drawn to this forum. I am in the middle of a 4002 motor repair and perhaps we can exchange information to help each other?

    Regards

    H H Scott
     
  3. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello HH Scott,

    I found out what my problem was. I had two motors from different tables that I was trying to get one of them to work and was swapping inside parts between them. One was totally defective. What I did not know was that the two motors were slightly different and the motor was not working correctly because the polarity was not aligned correctly when I assemble the motor parts. I have through this process I think created more problems with my main circuit board which I am now trying to sort out. I don't know if I can be of any help to you because of my sheer lack of knowledge. But I do appreciate the reply.

    John
     
  4. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    Hi John

    Thanks for your kind reply. This is a very long story but I'll be as brief as possible.

    I have owned the 4002 along with 2 other earlier versions for about 20 years. Long ago, I made a cosmetically perfect deck from bits and pieces from the other two. The internals of the older turntables are of course not compatible with the Series 5511 so I could use any parts from those except the wood surround and perhaps some aluminium bits at the top.

    After work was completed almost 20 years ago, it worked correctly for a few hours and suddenly, the speed became erratic.

    As I have many other turntables, I packed the 4002 away and tried intermittently over the years to see if I could get it to work but was unsuccessful.

    Someone gave me advice to replace the 4000uf 50V capacitor which I did which also didn't do any good.

    Fast forward another 10 or 12 years to last week, when I decided to have another go. By this time, the deck's arm didn't function but this I repaired quickly as the arm carriage leadscrew pulley was cracked in half. I fixed the problem by using the pulley from one of the other 4000's I have here.

    As the platter didn't spin at all, I dis-assembled the deck and removed the motor. I measured the rotor coils and found one coil was open circuit. Only late yesterday, I figured out where the 'other ends' of the coil wires are - one wire is soldered to each commutator tag and all three coil wires are twisted together and soldered at the rotor's underside.

    I have sufficient experience to repair the faulty coil which I will do in the next few hours but my biggest problem is the 3 diodes? soldered between thick tinned bare wire above the coils.

    These 3 'blobs' don't look like any diode I have seen. To me, all three look like porous carbon and if I measure them with my multimeter set to diode testing, the measurements don't make any sense at all.

    I don't know their value or specifications and I'm not even sure if they are in fact diodes.

    If you perhaps have any information regarding these parts, I would very much appreciate if you would be able to let me know anything about them - even an image of yours would help.

    I have many clear images of the motor's inside and I also discovered that it is crucial to re-assemble the housing parts correctly.

    There are more troubles - the brushes on my motor are severely arc'ed and are no longer serviceable. I will have to remake new brushes as it would be impossible to find replacements.

    Best regards

    H H Scott
     
    Last edited: Apr 19, 2011
  5. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello H H,

    I am not sure that the plastic "blobs" you are referring to are diodes but they may be. I could help you out with the spare inside coil that I have, if it would be of any help. I just don't know if it is faulty or not which may just be frustrating for you. Do you know about the Beoworld.org website? That is where I was trying to find help with the motor. Although I did not get much feedback about the motor there is a member that sells replacement kits for the capacitors for these tables. He uses the name of Martin and Dillen on the forum. It is the Beogram Forum on that website and you can post a message asking for him to contact you. Usually by this time most of these tables need the capacitors replaced.

    Regards,

    John
     
  6. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    Hello John

    Thanks so much for the kind reply.

    I think I have some better news regarding the motor. About 4.00am yesterday, I decided to act on a hunch. On the underside of the rotor, all 3 coils' wires are twisted together and soldered. On mine, the joint was coated with some brownish contact adhesive which I first removed.

    I then scraped the joint lightly with an NT cutter blade to give good solder contact and then 're-flowed' the joint with some fresh solder.

    I then measured all three coils again at the commutator tags and all 3 checked out at 23 ohms - no more open circuit at the one coil!

    Those 'blobs' are a strange electronic component. In fact, on our local AVSA Forums, some very knowledgeable blokes are still debating as to what kind of diode or even zener things they are. They think these things are there ro provide arcing of the brushes on the commutator segments. So, by the looks of things, it appears as if my motor's rotor could be useable again.

    The next step is to find a solution for re-making the pair of brushes. Mine are completely unserviceable as parts of the brush 'fingers' had arced so much that there's very little left.

    All of this work I have done inbetween 'regular' work. I have an urgent phono cartridge which must go asap to Australia so I will have to postpone further B&O work for a day or two.

    To make things more interesting, I was contacted today by B&O locally to find out if I can make a custom phono cartridge for local owners of B&O equipment. Before I can pay attention to this, I will have to put my 4002 into working order again..

    Regarding the B&O forums, they seem to want you to pay to subscribe to their forums.

    Over at vinylengine.com there's a member there by the moniker "beobloke". If I run into further problems, I may send him a private message there.

    I have taken lots of clear pics of work I have done so far on the 4002. If you wish to see some of them, you can send me a pm request for my email address.

    Best regards

    H H Scott/andre
     
  7. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello HH,

    That is very good news all around for you. Regarding the Beoworld website you can join as a bronze member and there is no fee. You will have to pay for a higher grade membership if you want access to the service manuals for the equipment however. I would love to see the photographs but the PM if I understand correctly says I won't be able to send you a message until I have sent 15 to staff. Totally not sure what that is about or maybe I am misunderstanding something.

    John
     
  8. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    I'm not sure what the exact limits are, but there are limits to prevent new members from using the PM feature to spam other members (and we get a LOT of spammers joining up). It also prevents new members using PM's for their intended purpose, which is unfortunate.

    You can post images to the forums, so you should be able to post the photos here.
     
  9. H H Scott

    H H Scott

    26
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    Apr 18, 2011
    Hi John

    @ (*steve*)

    Thanks for your advice.

    I will post a few pics when I have a chance a bit later. Perhaps other EF members will find them useful as well.

    Regards

    H H Scott
     
  10. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    Yeah. If you look at the reads on this thread, there must be a couple of people reading along (I know I am).
     
  11. H H Scott

    H H Scott

    26
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    Apr 18, 2011
    Hello (*steve*)

    @ John

    I'll start by showing a pic of the B&O deck I've had for so long and could never get to run correctly. All this could change over the next few days as I repaired the linear arm's function by fitting a replacement leadscrew pulley and new belt.

    The main problem however was the deck's erratic speed which I now know was due to an unserviceable motor with burned brushes and a dead coil. As posted earlier, all three rotor coils now have a dc resistance of 23 ohms and the problem was a dry solder joint.

    Next up is a major problem. If you look at the brushes, you can see these are no longer useable. The plan is to go and 'trawl' some electronic scrap places later today to see if I can find suitable scrap motors with similar-looking equivalents - maybe from a dead cassette player or rtor player and adapt these to fit.

    If anyone can recall seeing something similar, I would appreciate your ideas.

    Cheers all

    H H Scott
     

    Attached Files:

  12. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello HH,

    I have the brushes for a motor that while they have been bent are intact and not burnt like the ones you have I think. If you want them send me your address and I will get the bottom part of the motor to you. Did you have to unsolder the base of the motor to get those brushes out as seen in your photo?

    John
     
  13. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    Hello John

    The "urgent" unrelated work I had to get out before Easter left for Australia yesterday and I returned to the 4002 motor problem late this afternoon. For the past few hours, I have literally been grinding and milling replacement brushes which is extremely fiddly work and I will have just made two micro-sized copper/carbon blocks as brush contacts as there's no way that I will be able to make those beryllium 'fingers'. I am not even sure at this time if what I am making now, is going to work.

    I will be extremely grateful for your most kind and generous offer of a set of proper brushes from you. As mentioned, I have also two scrap models 4000 and some of these bits may likely fit your machine. So, if there is any other bit you require for your turntable I can send you in exchange - cosmetic outside or any internal part, please let me know.

    No soldering was required to remove the brushes. On my motor, each of the brushes was clamped by a screw and black, flanged insulating screw.

    I see above here is a PM facility and I will see hereafter if I can PM you my address.

    Best regards and happy Easter

    H H Scott/andre
     
  14. H H Scott

    H H Scott

    26
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    Apr 18, 2011
    Hi again, John

    I must log 15 messages the board advises. I have posted 11 X now and will try to log another few posts which should enable me to PM you my address.

    Cheers

    H H Scott
     
  15. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    PM sent.

    I don't know if I qualify to send PM's at this time as being a new member, my PMs may have to pass the Moderators first.

    Regards

    H H Scott
     
    Last edited: Apr 21, 2011
  16. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello H. H.,

    I was looking at the brush parts you show for your motor in the photos and am not sure that they are the same as mine. I will take some pictures of my motor tomorrow and send it along. If you have a 3 volt DC motor and it looks physically like mine I might just send the complete motor so you will have compatible parts. I am pretty sure the motor is not functioning however, but it sounds like with your skills you may make that happen. So far I have not received a PM from you with an address so not sure if that is working for you or not.

    John
     
  17. jfrancis

    jfrancis

    13
    0
    Feb 25, 2011
    Hello H. H.,

    Just saw that I do have a message from you with your address. I will send the motor along after posting the pictures so you know physically it will fit your mounting brackets.

    John
     
  18. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,482
    2,830
    Jan 21, 2010
    I just read them...

    Thanks for the considered input on a number of other threads. I appreciate that you went to the effort of posting several helpful and informative messages.
     
  19. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    Hello John

    Thanks again for your very kind offer. If I can compensate for the postage or out of pocket expense in any way, please let me know. I have some experience with these things and also have machining facilities incase something needs adaptation.

    Also, my offer of parts in exchange from my scrap 4000 series stands.

    Whatever you do decide to send, please mark the padded envelope? clearly on the outside - "Turntable Motor for Repair - No Commercial Value" incase our customs blokes get ideas.

    If this will help, I will post pics here of the faulty motor a bit later. It definitely is a 3V dc motor. The other motors I have look totally different as those are from the 4000 Series and are ac synchronous types and will not fit or be compatible with the 4002 decks.

    I'm a bit reluctant to post my email address as I do not want to be here for commercial reasons or gain but will again send you a PM with my email address, should you wish to contact me directly for whatever reason.

    Regards

    H H Scott/andre
     
  20. H H Scott

    H H Scott

    26
    0
    Apr 18, 2011
    Hi (*steve*)

    Happy Easter if applicable. Thanks for the kind words. I have been messing around with electronic and electro-mechanical things for several decades so if when I read the forum posts and know of an answer or solution for someone, I will always help where I can.

    I suppose one is never too old to learn something:) What I have found again and again, that as one gets older, you gain and retain experience on how to deal with all kinds of problems - from lawnmower repairs to breakdowns with electronically overloaded modern cars - there ARE always a way around fixing things, even if one has no formal electronics education as is the case here.

    My own motivation to try and repair things myself has been the dread of calling expensive technicians who is sometimes less knowledgeable than yourself and secondly, sometimes being charged exhorbitant and unjustified prices for their time.

    So, diy is always a first option for me.

    Regards

    H H Scott/andre
     
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