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Beogram 4002 (5521) restoration woes

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notwist
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notwist posted on Sat, Sep 5 2020 7:24 AM

Hi guys, 

I recently inherited two Beogram 4002 turntables with five additional brand new EN20 cartridges. Seeing that I love my B&O collection I decided to restore them as both were defective. The first Beogram actually was a succes on the first go; it was basically a transistor burnout, some failing caps and two resistors failing. It needs some alignment but I wanted to do this when the second one was done. Easier to do two alignments at the same time. 

That second one is proving to be more of a problem. It had three of the metal can transistors burned in such a way that i had to restore the tracks. I recapped the entire unit. I replaced most of the old 1w resistors that weren't in spec anymore, the other 2 seem OK. I did not touch any of the existing film capacitors. Now the machine at least doing 'something' besides being dead. I changed the belts using Dillen's replica's. 

When I power this machine on, either nothing happens or the carriage will start. If it starts it will move over the platter and then return to the base. Sometimes I can press the start button and it will actually work. Most of the time nothing happens. So. 

- Startup isn't working as it should (it starts by itself sometimes)
- Start button doesn't work; nothing happens (besides very intermittently see #1)
- 33rpm button: when depressed runs the motor but stops when released
- 45rpm button: nothing happens
- When the tonearm is working it starts at 20% of the record instead of the start. 
- When it does start it produces good sound at the correct speed
- The lamps all seem to be working (sensor, tonearm, selector etc). Perhaps not at the right intensity?

As far as I can tell from my other Beogram, the expected behaviour is that, when plugged in, nothing happens. When you press the start key it will scan the record once, then return. Then you can press start again and it will actually start playing. 

I have read through dozens of posts on this brilliant forum and it strikes me that these problems have all been encountered multiple times in one way or another. But because there are so many posts on these subjects what i'm hindered by is that same multitude of posts. 

Who can set me off in the right direction? Which problem (or interconnected problems) should I tackle first? This machine can be daunting at first. I don't want to introduce more problems of course. 

Many thanks for your help and guidance! Hope to restore this second one in pristine condition as well ;-). 

Regards, 

Bert

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notwist
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Hi Sonavor, 

This afternoon I had the time to align the diaphragm; basically all it needed was a slight nudge to the right. I did some finetuning using the eccentric screw but it was essentially not really necessary. As far as mechanical adjustments go, this was actually a whole load easier than expected. Based on the SM and your explanations I really had some cold feet, ha ha ha ha. Of course the biggest hurdle to overcome was my latent hatred of mechanical stuff, I am used to working in an electronics lab ;-). 

Now the only thing I should check is the RPM. It's running a little slow, 5% off perhaps. I don't have your cool apparatus so i'll have to do this one by ear. Let's hope the trimpots are in reasonable condition but I may change them out as a course of maintenance. 

Also I need to double-check running a full record if it will shut off at the end. Fingers crossed! 

I do think that now the machine has a chance of working fully again! I'm lucky this forum exists as these are inheritance pieces which mean something to me besides being nice turntables. Your help and patience have been monumental, 1000x thanks for this. 

Now I still need to do a Beocenter 8500. That one has the bezel in 5 pieces and the glass loose. Of course, it being B&O there are several other problems as well. Full revision is in order but after this 'ordeal' I am up for a challenge ;-). 

Kind regards, 

Bert

sonavor
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Hi Bert,

That is good news. You over that hurdle now.

Yes, the RPM measurement tool that Beolover makes is really nice. Prior to that I tried one of those optical RPM measurement tools that read pulses from little reflective strips you place on a rotating object. I used an old record but the resolution on the measurements were not consistent enough and not much use.

A great thing about the Beolover RPM tool is that it can connect to a computer and you can record the measures for a long period of time in order to check the stability. That reveals problems with the platter motor and other related components.

If you haven't yet done so I would recommend having the platter motor restored with new oil infused into the bearings. I would also replace the RPM speed adjustment trimmers on the main board. Those changes will give you a big improvement of the turntable speed stability.  

-sonavor

notwist
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notwist replied on Thu, Oct 15 2020 11:37 AM

Hi Sonavor, 

I have done all the additional tuning and alignment steps and after some weeks I can say it plays wonderfully. Again I would like to thank you for your help in making this unit play again. Another one saved from oblivion ;-). 

Now I need to start working on a Beosound 9000 (power supply problem) and a Beosystem 8500 (many issues and the glass plate is completely off). 

But for now, very happy! 

Regards, 

Bert

Filip
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Filip replied on Fri, Oct 16 2020 2:02 PM

Good job.

mr_anders_son
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Hi!

I have a 4002 where the left channel is lower than the right.

I have check with two different RIAA.

And the pick-up is ok!

What can I do?

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sonavor
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If the problem is with the Beogram 4002 then it has to be a connection problem somewhere with the signal in the path from the cartridge connector in the tonearm to the phono cable coming out of the Beogram.

There is no amplifier or any components the signal goes through unless you want to count the muting relay. But then it is really just a switch.
So in that signal path you are really just looking at connections. Nothing that would attenuate the audio signal. I suppose a bad connection could do something like that but usually bad connections exhibit themselves as sudden on and off events with the signal.

You can try wiggling the phono cable connector where it attaches to the output board (near the muting relay).  You can also tap on the relay.  
Another thing to visually check is the physical condition of the pick-up connector of the tonearm. Look to see that it doesn't have any cracks and isn't loose.

I would still suspect the pick-up. What tests have you done with the pick-up to know that it isn't the problem? 

-sonavor

Dillen
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Dillen replied on Fri, Oct 23 2020 6:20 AM

sonavor:

There is no amplifier or any components the signal goes through unless you want to count the muting relay. But then it is really just a switch.

And the muting relay cannot break the signal path - only ground it - so a failing contact in the muting relay would cause the affected channel to not mute.

Martin

sonavor
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Good clarification Martin. 

John

mr_anders_son
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Ok thanx for answerSmile


Can of course be the pickup. But when I remove and insert the left channel plug several times in the RIAA, it works. The DIN plug is new so there is nothing wrong there. And as I said have tested with two different RIAA.

BeoVision Eclipse 55"...BeoLab 5 FRONT....BeoLab 4000 as REAR....BV5 HD....Beoplay V1-40....BV10-32....BC6-26....Beosound 9000....Beosound 1 New York edt....Beosound Stage....Beoplay S3....BeoRemote One BT....Beo6....Beo4....Beo4 Cinema....BeoLink 7000....Serene....H9i Rimowa....6 x H6....Form 1....U70...

mr_anders_son
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Ok thanx for answerSmile


Can of course be the pickup. But when I remove and insert the left channel plug several times in the RIAA, it works. The DIN plug is new so there is nothing wrong there. And as I said have tested with two different RIAA.

BeoVision Eclipse 55"...BeoLab 5 FRONT....BeoLab 4000 as REAR....BV5 HD....Beoplay V1-40....BV10-32....BC6-26....Beosound 9000....Beosound 1 New York edt....Beosound Stage....Beoplay S3....BeoRemote One BT....Beo6....Beo4....Beo4 Cinema....BeoLink 7000....Serene....H9i Rimowa....6 x H6....Form 1....U70...

sonavor
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Are you saying that you can sometimes get full sound out from the Beogram 4002 with your cartridge (via one of your RIAA amps)?

-sonavor

mr_anders_son
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sonavor:

Are you saying that you can sometimes get full sound out from the Beogram 4002 with your cartridge (via one of your RIAA amps)? -sonavor

Both my RIAA.

BeoVision Eclipse 55"...BeoLab 5 FRONT....BeoLab 4000 as REAR....BV5 HD....Beoplay V1-40....BV10-32....BC6-26....Beosound 9000....Beosound 1 New York edt....Beosound Stage....Beoplay S3....BeoRemote One BT....Beo6....Beo4....Beo4 Cinema....BeoLink 7000....Serene....H9i Rimowa....6 x H6....Form 1....U70...

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