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Beogram 4000 repair

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pauldvern
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pauldvern posted on Fri, May 10 2019 5:38 PM

Hi,

I have recently dug out my fathers Beogram 4000 which he bought new in 1972. It's been sitting in my childhood bedroom cupboard since breaking down in the 80s. After putting a plug on the old girl I discovered that the tone arm would not move and the platter did not rotate, all it would do was light up and lower and raise the arm. I took it to a local old hifi repair shop who said that there were some teeth missing off the cogs and there are no spares, when I asked if there was anything electronic at fault he said no, which I found odd.

I am an engineer and as a youth was an electronics nerd, so faced with the diagnosis I'm up for the challenge of getting the thing going.

If anyone can advise me where to start and point me at useful info I would be truly grateful.

Cheers

 

Paul

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joeyboygolf
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I wonder who fitted the cogs and teeth 'cos I'm fairly sure it wasn't Bang and Olufsen!

I have worked on these in the past but it is some years ago. We have experts on this forum who will be with you soon.

I suggest you don't attempt to fire it up again until you hear from someone knowledgeable. You have a gem to play with but it will need some restoration.

You will need the service manual which is available on site for silver or gold members.

Regards Graham

Craig
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Craig replied on Fri, May 10 2019 8:35 PM

Paul

Congratulations.....there are lots of thread in the forums to provide all kinds of guidance for this type of exercise, I have just been through one myself, was great fun...you could start by downloading the service manual, reading it to get familiar...how to dismantle etc...then have a look inside to ensure all the belts are in place...a good idea is to make sure the stylus had a cover on it (or take it off) before going too far....take oics and post them for us to help you along..

Craig

sonavor
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You can't take a turntable like the Beogram 400x series to any hi-fi repair shop. It is over forty years old and requires the knowledge of someone familiar with them. A lot of the problems after sitting for so long are likely with connections involving sensors. The Beogram 400x is an old fashioned analog control system and has to have good inputs from all of its sensors. Some sensors are just switches while others are optical driven (a light source to a light sensitive device).  No cogwheel I'm afraid.

There are plenty of threads on this forum and on the Beolover Blog that can give you an idea of the scope of work involved. 

In any case your Beogram 4000 is a highly collectable turntable so I would send it to the right person for restoring.

-sonavor

pauldvern
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Thanks chaps,

I have now upgraded and downloaded the manual. The guy going on about cogs seems quite bizarre. Maybe its some BS code for "I don't want to deal with this" , he did come highly recommended too. Anyhow, I will now read up over many cups off tea and get back to you when I have got a little further.

 

Paul

sonavor
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He could well be very capable but working experience and/or willingness to dive in and learn is required for these vintage Beogram turntables. They can't be compared to anything else out there.


-sonavor

pauldvern
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Hi all,

 

I have now got my Beogram back from the dodgy cogs man. I have started to go through things and have identified some faults.

Firstly the little black motor that turns the threaded shaft that moves the arms, it screams like hell! Some sort of bearing problem I am guessing. The belt coming off it also slips so should be replaced but is not the source of the noise.

The platter motor only turns half a rotation and then just vibrates. I've started through the fault flow diagram in the manual, I am getting 24 volts at 1R19 so the PSU is working. The next thing to check is the oscillator at TR7/8 but I don't have a scope any more so I am stuck. I suspect this area is faulty and the motor is not getting the correct signal to run.

If anybody has worked on this bit or the arm motor any tips would be gratefully received!

Cheers

 

Paul


sonavor
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This website has a bunch of restoration blog posts for Beogram 400x turntables you can get photos and information from that will familiarize you with the task. This section specific to the Beogram 4000 even has some videos you can watch regarding some of the restoration checks. 

Regarding the noise you hear from the platter motor, do you hear the noise when you remove the little belt?

-sonavor

joeyboygolf
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Correct spec belts can be obtained from member Dillen (Martin Olsen) on this forum.  Do not be tempted to buy from ebay as they are usually sub standard.

The tension on the servo belt is critical if you want to achieve the correct movement of the carriage.

Regards Graham

pauldvern
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Thanks Graham, I have asked Martin about belts.

pauldvern
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Hi everyone,

 

We have success! 

I replaced the tip31/32 transistors in the motor drive circuit and I now have a turning motor. I have adjusted the motor voltage with my scope but I have some funny blobs on the trace. Could this be my motor capacitors? I have ordered some new ones anyway.

I dismantled the servo motor and added a little lubrication, it's now much quieter.

Just waiting for my belts from Martin and we should be spinning some tunes!

 

Cheers

 

Paul


pauldvern
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Hi all,

 

I have received by belts from Martin, many thanks!

Sadly I have to now delve into fixing some logic issues. The Beogram does not see the record on the platter, it does not stop at the 30cm point and just continues to the centre. The light in the arm is on. I can stop the arm and lower it manually. Going through the fault finding in the manual it seems to point to 3IC7 being faulty but the voltage at BS is sort of middle not low or high.

I think I'll be doing some switch cleaning and measuring again.

 

 


Craig
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Craig replied on Tue, May 28 2019 7:56 PM

Ok....before you check 31C7 or do any more work anywhere else check your power supply voltage levels and also the condition of the power supply capacitors....I have been down this road recently and discovered that a lot of the difficulties where due to the power supply capacitors failing under load, replace them first then look again, check my thread "a beogram 4000" and see if there are any similarities 

Craig

pauldvern
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Thanks Craig, I’ve ordered some capacitors, my power voltages are correct but they don’t look very smooth on the scope. I’ll check out your thread. 

 

Paul

Craig
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Craig replied on Thu, May 30 2019 4:36 PM

Paul

See link below to the thread as per your request....

Craig

 

https://forum.beoworld.org/forums/t/35317.aspx

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