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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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ALF
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ALF replied on Sat, Sep 5 2020 8:07 AM

Hi Bert,

when you press the 33 button the platter keeps spinning as long as you keep the button pressed. - it is the record-cleaning function.

doing the same with 45 isn't doing anything at that stage, it only switches the speed to 45 after start has been activated if so desired.

check the contacts under the keyboard to make sure they are clean and not touching anything they shouldn't without pressing the asigned button.

have you checked the positioning ruler ? If that has shifted the arm lowering  point would be wrong.

hope that is helping.

ALF

notwist
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Ah okay clear, I was under the impression that the 33 button would keep spinning as a manual speed selector. Obviously rtfm for me in this regard ;-). 

I have cleaned the keyboard and the contacts using emory paper and Deoxit D5. So they are clean and making good contact when pressed. Nevertheless the start button never seems to do anything, it only does something when the turntable is powered on and starts moving on it's own (first pass). 

Let me check the ruler, as far as I can see that is in the correct position. My first guess would be that some sensor is off base / out of alignment. But I am most certainly not an expert on this turntable's exotic design. Could just as well be something on the main PCB or, horror, the relay or one of the IC's. 

Bert

notwist
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I checked, everything is in place as I think it should be. The same as the other 5521 Beogram. 

I've tried to find the service manual for this type but couldn't find it. Is there another one from another type that is compatible? 

Thanks, 

Bert

Filip
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Filip replied on Sat, Sep 5 2020 7:51 PM

Hi,

Firstly, pressing the 33 RPM button works as it should. It's for cleaning records and will only spin as long as the button is pressed.

Secondly, the other deck is not supposed to scan the record first before you can play it. I suggest you take a look at the mechanical adjustments of the arm distance to the platter. It should be 23 mm measured from the top of the arm with the bulb to the platter. Only then will the optical sensor be able to see correctly if there is a 12" or 7" record on the platter.

sonavor
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Filip:

I suggest you take a look at the mechanical adjustments of the arm distance to the platter. It should be 23 mm measured from the top of the arm with the bulb to the platter. Only then will the optical sensor be able to see correctly if there is a 12" or 7" record on the platter.

I don't believe that is quite how it works.

The 23mm distance is to set the height of the fixed arm which in turn is used to set the position of the tonearm. That properly sets up the angle at which the Beogram phono cartridge stylus will meet a vinyl record. 

The fixed arm detector lamp and sensor detect the pulses of an empty platter and determine if it is okay for the tonearm to lower. That sensor lamp and and voltage signal should be checked using an oscilloscope to make sure it is well within proper operating range.

The set down position from start is determined by the tangential position sensor and scale along with two switches (ES - end stop and SO - switch off).  There are tab actuators on the sliding tangential arm transport that engage the two switches. There is another photo sensor and lamp that read the pulses coming off the position scale that determine position for set down and the run-off groove. That sensor is another item that should be measured to make sure it is properly within operating range.

The tangential arm transport and sensor scale have position adjustment screws to fine tune where they need to sit for the Beogram to operate correctly.

There are quite a few other adjustments to check. They are listed in the Beogram service manual. I suggest familiarizing with those if you plan on maintaining your Beogram yourself.

-sonavor

sonavor
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Regarding the service manual...
Your Beogram 4002 Type 5521 should be very similar to the Type 5523. It you can't find those you can look at the Type 5513 as it is very similar.

If your run into something you can't find the answer to then post some photos and someone here on the Beoworld Forum should be able to answer it.

-sonavor 

notwist
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I have indeed now read the 5523 service manual. Based on the manual and some experience I changed:

- All old 1 W resistors + old ½ resistors
- I changed all the basic motor transistors surrounding the burned out ones. They still tested good but HFE was way off
- In the PLAY circuit I changed the base diodes running into the power supply
- I changed all the old Philips film capacitors; some were breaking

Now the PLAY function works! Yeah! 

I had already lubricated everything and it is smooth now. 

One final problem remains, which is that the start position (start lowering onto the record) is incorrect. Instead of starting at the start groove, it will start roughly 15% inwards. 

I suspect this is an alignment issue, but which one? 

Regards, 

Bert

notwist
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Hey there, 

damn I was really convinced that the 'scan once, play second' was the expected behaviour ;-). 

Now that I have repaired the other machine your remark makes sense as it doesn't have this behaviour. But the second previously broken deck is not playing at the start position (start groove) but starts at roughly 15% inwards. 

My guts tell me this is probably an alignment issue but I can't remember where to start. 

Regards, 

Bert

sonavor
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Did you check the Photo darlington adjustment on page 4-2 of the service manual. That sets the voltage on the 4IC1 collector to 5V.  Perhaps that is out of adjustment and causing a problem in the detection of the set down position.

Also, you want to adjust the position scale so that it is very close to the slit where the sensor is.  If it is too far away then the sensor may not detect properly. 

-sonavor

notwist
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Hmmm. I double checked but I can't find any issues with it. Voltage seems to be OK. 

I understand the repositioning of the position marker, but isn't it true that playing with this will only give me roughly 0.7cm of play? That is not enough as the drop point is about 2.4cm inwards. 

Of course I will check again, little bit hesitant to changing this as it's easy to mess up alignment. Don't want to introduce more issues. Dicking around with mechanical parts is often a sure way to create a mess. 

 

notwist
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The position marker was at the complete left, I moved it to the middle and the complete right. Neither change has an bearing on the lowering mechanism. It still lowers roughly 15% too far into the record. 

Is this not indicative of a failing lamp in the sensor? Perhaps the brightness is off because of the age of the lamp? Just thinking aloud here, this thing is way over-designed technically so the actually issue can be a silly as an old lamp........ 

notwist
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I have read and reread the service manual but can't find a clue as to any alignment of the tracking system or circuit. I think this is odd. I can't help but imagine that the issue (15% off from the start groove) is something that must have happened to people before. I also can't shake the feeling that it has got something to do with the lamps. 

I found the beolover article (https://beolover.blogspot.com/2018/01/beogram-4002-5513-restoration-of-arm-lowering-and-tracking.html) which describes a change on the basic system. It seems that the light intensity is rather vital. In my mind it would thus be reasonable that, if something is off with my system in this regard the tracking would also be off. 

But I am really hesitant to just muck around. This turntable is over-designed to a point where just randomly doing stuff can and will result in even more problems. 

Can anyone give me pointers on this problem? 

sonavor
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notwist:

The position marker was at the complete left, I moved it to the middle and the complete right. Neither change has an bearing on the lowering mechanism. It still lowers roughly 15% too far into the record. 

Is this not indicative of a failing lamp in the sensor? Perhaps the brightness is off because of the age of the lamp? Just thinking aloud here, this thing is way over-designed technically so the actually issue can be a silly as an old lamp........ 

That is what I was referring to. It sounds like you tried repositioning the scale left and right which is fine to try but you did not adjust it in and out to be closer to the sensor. The lamp can be suspect if it is still original but that can be compensated up to a point by the service manual adjustment using trimmer 1R88.  I showed the adjustment here.  I had a Beogram 4002 one time that was not detecting the run-off signal generated by the position sensor. I monitored the signal with a scope and saw there was no signal until I re-positioned the scale closer to the sensor. 

I am not saying that is your problem for sure but if adjusting the scale left or right doesn't fix the problem then the issue has to be with the sensor and when it does detect the black marks on the scale. It sounds as if your Beogram is not registering the first set down mark on the scale. Can you post a photo of your scale? Are the black markings all there and correct?  This old post I made shows a couple of good photos of the Beogram 4002 position scale.

You say your set down point is about 15% off. The set down point for a normal record is the 30cm mark on the scale. It appears your Beogram is not detecting that mark (is it missing or worn?). Instead your Beogram detects the 25cm mark which is 15% in.

-sonavor

notwist
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OK clear, thank you very much! I am so happy with these pointers, the exotic layout of the turntable makes it too easy to mess things up. 

I will check this in the lab next thing tomorrow. It's very late now, too many projects and too little time. By my knowledge the ruler looks OK, but I will check that as well. 

Thanks!  

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