ARCHIVED FORUM -- March 2012 to February 2022READ ONLY FORUM
This is the second Archived Forum which was active between 1st March 2012 and 23rd February 2022
Hi Sonavor,
no I didn't confuse the measurements, same as per service manual. Ground is either chassis ground or a ground point (tried several methods to see if the results changed, sometimes this can happen). Measurements were taken from the correct point of the phototransistor. It seems that on a transparant position the voltage drops way too much, certainly if the target is 5v. The roughly 1v is enough for the phototransistor to work, likely not to full capacity though.
It's a bit late over here now but tomorrow I will check them again. If only because I want to be sure about this. But if that trimpot should give this voltage then it is 99% busted for sure. Which is not out of the ordinary for these trimpots at all, they are old and this board is not revised.
For good measure I will also trace the paths of the power lines. See what could interfere with the circuit that can cause the voltage drop.
Kind regards,
Bert
I did the first tests as you asked. I have used the same positioning as you have for the scales, as in the photos you sent.
With the platters removed (both the lower and upper) on >> start the assembly will move to the start position. It will lower the tonearm. But the trolley keeps moving. So while lowering the tonearm the trolly moves to the left. Slowly at first and then faster until it reaches the end point. After which it returns to the start position (null position). This is decidedly different from your expected behaviour: -> at the 30cm mark -> stop trolley -> lower tone arm -> end of sequence (stay in this position).
As for the voltage on the 4IC1. I believe I made a mistake myself working with a multimeter in the lab that uses different readout (dumb I know). Using my own home lab, the actual voltage on a transparant part of the scales is 9 volts (not 0.9v). Using the trimmer 1R88 I can bring the voltage down to 7.2 volts. That's it, this is the lowest position of the trimmer. Which appears to test OK.
For 1TR17 I can bring the voltage to 0.7v using trimmer 1R88. But of course, this will also bring the voltage of 4IC1 up. It is the same trimmer so changes on the trimmer will effect both. After trimming the position sensor to 0.7v the phototransistor 4IC1 registers at 9.4v on a transparant section. Lowering this to the lowest position (7.2v) will set the voltage at 1TR17 at 0.789 volts. As a techie this interdependency is odd, are we sure there is only 1 trimmer to set both voltages?
In any case, it is impossible to bring down the voltage (as per SM) to 5 volts. So something is broken inside the circuit. I am going to check if I can find what is causing it.
Hi Bert,
You might try experimenting with the LED position and the trimmer to adjust that service manual voltage. On your other issue - arm lowering and the transport continuing to move the arm forward...That is the expected behavior when the tracking sensor is out of adjustment.Read through the adjustment procedure in the service manual and you can see the adjustment points in the links I sent.
The first thing I like to do is recalibrate the tracking sensor adjustments so that the eccentric adjustment screw is at its center position. That way I have room to rotate it left or right as needed. So after centering the eccentric screw I use the screw that mounts the bracket (with the slit for the lamp to sensor) to the tonearm base...to adjust the assembly so the tonearm does not move forward when the arm is lowered. I want that to be my starting point.A caution when adjusting that bracket mounted to the tonearm base - It rotates left and right but it can also slide up and down. So be careful that it doesn't slide downward where it hits the housing for the sensor. The service manual says that the bracket with the slit should sit about 1mm above the sensor housing.Now with the tonearm tracking sensor centered it should lower and not move forward on its own. You can test the sensitivity of its centered position by lowering the arm and nudging the tonearm towards the center spindle. Doing that should cause the Beogram tracking to advance the position.I like to set this starting point where it barely requires a nudge to start the tracking. This means the actual adjustment procedure should require very little adjustment of the eccentric screw.Also note - turn the adjustment screws very slowly when tightening them as you could accidentally change the position of the setting....and also - DO NOT OVER TIGHTEN anything. I come across so many components where someone over torqued a screw. You don't need to do that on an audio component. They aren't an automobile.
The service manual will call for a specific test LP from B&O. I have never been able to find that so I use some old LPs I own and an old MMC phono cartridge.The manual says to disconnect the platter belt and rotate the platter manually for this adjustment.I lower the arm on two or three tracks of my test record. Then I rotate the platter and observe the tracking motor. The motor should advance the arm within a couple of platter revolutions the first time around then every revolution after that.-sonavor
I sent you a reply but the reply is held up in moderation for some reason. Hopefully it will be released soon.
-sonavor
No problem!
I'm working early hours in the weekend on a project that has to be finished before Monday, I will see it passing by when it's out of moderation ;-).
I had some spare time today and decided to look at your notes to see how best to tackle the dismantling. As a good friend says "Am am an electrician, not a damn mechanic". It's always daunting to take such a piece apart and you need to prepare yourself. Easy to mess it up. And I will need to soak the screws because up to now most of them have been difficult to remove (it's age, they get stuck).
But as I was testing the Beogram, the trolly now doesn't lower anymore. This is after the test I did last night (so without the platters). It now does this same behaviour all the time. I can hear the 'click' on the 30cm border, but it just moves ahead. On the 45rpm border it switches to 45rpm (I believe this is OK). On the end groove it stops, returns the carriage to the 'null' position and stops both the carriage and the platter motor.
Is this expected behaviour after the test I did? Otherwise it would seem a new failure has occurred. I could not find a flaw in the circuit for the detector unit, it all seems to be OK. Even the trimpot reads fine. It's just that the voltages were off by a margin on the phototransistor.
Your knowledge is appreciated!
Oh yes, manual lowering the tone arm also doesn't work. This did work before. Really odd machinery. Then again, it's B&O and after my Beomaster 9000 restoration I thought I knew most of the quirks. But it seems this is another B&O headache ;-).
Hi Bert,I guess I have restored enough of them where I don't really find them odd.However, they are complicated and there is a big learning curve. Unlike the later Beogram 800x series the 400x do require some mechanical aptitude.Without actually being able to see what you are doing it sounds like you are making a lot of adjustments. I would recommend one issue at a time.You had the position sensor, ES and SO working earlier. Even though I don't think that the sensor voltage is completely correct. What did you change that broke that? I would recommend measuring the sensors of your working Beogram as a point of comparision.When you are testing the lowering do you have a cartridge attached? Is the tracking force weight adjusted?If you dive into some mechanical adjustments be aware those can be tricky.Always remember that those same parts came out of the B&O factory with everything aligned perfectly. So if you can't get something to adjust or line up properly then it has to be due to some other mechanical adjustment being incorrect or too far out of alignment.I have never had a Beogram 400x turntable that couldn't be adjusted back to the correct state. Getting there can sometimes take a while and requires quite a bit of iteration and patience.
Hope you are doing well, over here the sun is shining and it's actually warm outside (for a change). Unfortunately I am mostly inside working.
I did not do anything before, symptoms simply appeared. Now this is not my first European machine so I know from experience where many of the problems arise from. So I checked, double-checked and replaced several components on the board. Seeing as I had some spare time I also replaced all of the capacitors (this was an unrevised board). Now it is primarily film / mlcc. The transistors that govern the arm movement were out of spec, BC tiredness we call it. Not by much but often enough to whack the circuit. I replaced these. I also reflowed the entire board, this is basic maintenance on these B&O boards actually.
Now the Beogram is 'working' as before and is actually quite a bit more responsive.
I have spent over an hour determining what is actually going on. I think I can narrow it down to the carriage. It is not the sensor array, it is picking up the correct position. What happens is that, even on manually lowering the arm, the carriage moves to the left. It should not do this. It should stop, remain stationary and drop the tone arm. I can see that on lowering the tonearm, the drive spindle is turning at least half a turn. It should not do this, it should only move when the entire carriage is moving (manually or automatically).
So, I think that this spindle is out of order. It moves when it should not move. That is also why the tonearm is lowered too much into the record. My question would be, for my understanding, why it would move at all. What governs the movement? Is this a mechanical issue, does the spindle rely on a specific component or are it's movements set through another circuit?
Sonavor, as you said you have seen many of these tables. Please excuse me if my questions seem half-assed to you, I am also trying to understand and separate the mechanical from the electronics.
In my last two responses I explained why the drive spindle is turning. The adjustment of the bracket with the slit (diaphragm adjustment) and the sensor position are out of alignment. There is a procedure described in the service manual to adjust that.The service manual mechanical adjustments are described in section 3. Section 4 contains the electrical adjustments.Section 3-5 contains the adjustment for the tracking sensor - Adjustment of diaphragm.I have also seen a case where a mechanical adjustment is out that also affects the tonearm lowering. The distance between the tonearm and the fixed arm should be 7.7mm. Somewhere along the life of one of these Beogram 400x turntables someone likely made an ill advised adjustment to change that.Sometimes you will see a BG400x tonearm lower and the arm pull left or right instead of straight down. That indicates a mechanical mis-adjustment somewhere. Those can get tedious to fix.Your issue appears to be the tracking sensor adjustment.
Thanks, please excuse my questions as I know they can appear either stupid or 'I told this already' type. But the school i'm from is the 'first understand, then tinker'. I can accept that the cause of the problem is misalignment of the diaphragm. But I simply don't understand why this has a bearing on the spindle drive.
That is what is confusing me.
Also, reading the SM the final sentence is 'make sure that the arm has made an inward movement before the pickup lowers'. As I see it, that is exactly what is happening. An inward movement of the spindle drive after the correct position has been met. I don't see the relation between the spindle drive and the diaphragm, this is my lack of experience.
In the same vein: I don't understand why, when I manually want to lower the tone arm, the spindle drive still pushes it inwards. That makes it impossible to actually drop down on an exact spot; that can't be right. Imagine the users crying foul ;-).
Or, and this may be a complete misunderstanding; the diaphragm is the entire housing of the tonearm and sensor arm. What the service manual means to say is that you are actually moving the entire housing to the right (near the case). But then I still don't understand why the tonearm in manual mode doesn't simply drop on the specified location.
I have measured the distance, it is exactly 7.7mm so this it just fine :-).
Please please please, don't take my questions as a sign of not reading your remarks. It is simply a need to understand what is what and WHY it is so, before I go and do things on this machine that I have never done before. It is simply too easy to f**up such an alignment, you need to know what and why you doing things.
The Diaphragm or Diaphragm Arm is part #245 in the service manual. It is a bracket that a single screw fastens its clamp to the tonearm base. It turns as the base turns (i.e. when the stylus moves towards the center of the record). The Diaphragm Arm has a flat, horizontal piece the sits between the tracking sensor and its lamp source. There is a slit in the Diaphragm Arm that lets the light through. The position of the Diaphram Arm is coarsely set with the bracket and screw. Then it is finely set by the eccentric screw. There is not much travel in the fine adjustment eccentric screw so as I said previously, I first do the coarse adjustment where the tracking sensor is close to moving the arm forward but not fully...so that it drops straight down without moving. After that I can easily use the eccentric screw to fine tune the sensitivity so the tangential drive advances the arm every revolution of the platter. Notice that the service manual is pretty lenient with the revolution sensitivity calibration here. It says to make sure the tangential arm servo first regulates the position after 2 +- 1 revolution and every revolution after that. So at stylus set down the servo could adjust between 1 and 3 revolutions. I normally see it start after 1 to 1 1/2 revolutions.I can't say what the last sentence in the service manual procedure means. It is after the instructions to lower the arm and adjust the sensor sensitivity have been made. When I adjust mine I expect the stylus to set down at the spot I cue it to.When you lower the arm with the platters removed does the arm lower and the tangential servo slowly drive the spindle and move the arm forward (until the ES is reached)?
Okay that is a clear explanation, I have a better picture of what it is I need to do and why. I have taken enough pictures in order for me to reset it to the position that it is in right now. I always make visual references whenever I need to change a mechanical part, it is just so damn easy to make a mistake and be much further away from where it is right now.
But as I see it the main problem is that the carriage is making an additional quarter turn. I believe, without any experience, that this is the primary cause. I have made a video that shows the behaviour. As you can see in the video:
https://youtu.be/y7z9qSkuzvY
- On automatic delivery it travels, then clicks at the correct location, then travels more and then the arm is lowered- On manual control: when I press down, the spindle travels roughly a quarter, then the arm is lowered
As I see it, that is the primary cause for the tone arm not setting in the start groove. The sensor is working and stopping correctly. But then the spindle makes an additional movement, it is this movement that is the cause of the problem. It should stop, lower the arm and then only move when the arm is down and moving inwards. At least, this is what the service manual is telling me.
When I remove all platters, press automatic:
- The carriage moves to the correct 30cm mark- The spindle makes an extra quarter turn- The tone arm is lowered (this happens while the spindle is making the extra quarter turn)- The carriage continues to move inwards- When the 45rpm mark is met it shows on the panel- On the end stop it stops and returns to the start position
Again, I think this is correct with the exception of the extra movement of the spindle drive. It is as if the spindle gets an instruction to make that extra quarter turn immediately after it reaches the stop position. You can see this behaviour in the video.
All belts (also the spindle belt) are brand new from Beolover so they shouldn't be the problem. I can't ascertain if the spindle movement is an alignment issue or an electronic problem; it could be both.
Perhaps this is why I am confused about changing the diaphragm alignment as I don't think that is specifically connected to the movement of the spindle. At least not from reading the circuit diagram, they seem to be sequential (one after another). Perhaps there is another condition I am missing at this moment.
notwist: When I remove all platters, press automatic: - The carriage moves to the correct 30cm mark- The spindle makes an extra quarter turn- The tone arm is lowered (this happens while the spindle is making the extra quarter turn)- The carriage continues to move inwards- When the 45rpm mark is met it shows on the panel- On the end stop it stops and returns to the start position Again, I think this is correct with the exception of the extra movement of the spindle drive. It is as if the spindle gets an instruction to make that extra quarter turn immediately after it reaches the stop position. You can see this behaviour in the video.
The extra movement you are seeing is still the result of the tracking sensor being out of adjustment.The tracking sensor is sensing arm movement (even though there may be none) because the sensor is not adjusted correctly.The sensor is telling the control system to advance the arm. You can see that happening when the carriage continues to move inwards after it lowers.
I replied to this but my responses keep being sent to moderation for some reason. I guess the response is in quarantine. :-)
It was. Not sure why.
Martin
Okay clear! On the one hand I feel like an old fart and on the other like one of my students asking so many questions. Maybe my trepidation is coming from past experience working with mechanical parts but also from tuner alignment; you lean quickly not to mess around with things unless you know what you are doing. Because this Beogram is rather exotic it makes my skin itch if I don't really know what I am doing and why.
But I will go ahead and try to do the alignment. I think it will be tomorrow because I have a huge backlog of small tasks I need to finish before the end of the week. Normally there would be some spare time for this but it's the end of the year so many projects nearing completion and many small projects entering the fray.
Please let me thank you for your patience!
I will report back once I have tried the procedure, wish me luck ;-).
It is good to error on the side of caution. Never be afraid to ask questions first.
Yesterday I had time to do the alignment but the screws had seized (it happens all the time). I have treated them with our soaking liquid and then the usual heat treatment. Today I was able to loosen the screws without damaging them.
I have created a 'manual' from your replies and actions to be taken. I have created a bed for the diaphragm so that it can't fall down when moving it left / right. I have marked all positions and photographed them. This is alignment 101.
But looking at my 'manual' I realise that I don't really know what my target is. What I mean to say is, while the SM says things 'clearly' and your text is also clear, it is from the view of those 'in the know'. There is nothing there that doesn't make sense. And at the same time I am still struggling to determine what it is that I am looking for, what my actions are going to be.
A stupid example: you say to start with the coarse alignment (loosening the screw of the tonearm bracket). But what is coarse? How many millimeters? To that same effect: based on the symptoms do I move it left or right? By how much? What is the general target, make the sensor hole larger or smaller?
Then there is the 'eccentric' screw (nice term btw). It is for fine adjustment. But what am I actually adjusting with it? You say that you like to center the screw (centered position) This sounds logical but then I realised that I don't know that the centered position is ;-). Nor what I am actually doing to the assembly by doing so. What (if anything) does the eccentric screw move, how much does it move and what is the basic target (left / right / up / down)? Are we talking a millimeter or more?
This may all sound like noise to you. But my experience is, amongst others, in aligning tuners where turning a few coils the wrong way can result in goddamn disaster. I've spent countless hours trying to 'heal' a patient where Hobby Bob tried to do an alignment messing up the whole tuner.
Right now the Beogram is 'almost there' but I am worried that if I just start mucking around it will quickly devolve into a mess. I don't want to spend hours recalibrating my own mistakes. Hope you understand this.
Nice progress. Hopefully I can further clarify some things a little more here.
The eccentric screw center position is something you have to determine by observing the screwdriver handle. Note the far left position, then the far right position then kind of eyeball it for a center location. The goal here is really to make sure you have a little room to rotate the screw if necessary for the final tracking adjustment.
On the coarse adjustment using the diaphragm arm...There isn't really a marking or ruler measurement to make for the adjustment.Your feedback for the adjustment is how the sensor is reacting to the position you have set the diaphragm arm at.I do this adjustment with the platters off.Start the Beogram and lower the arm either manually or let it lower automatically at the 30cm mark.The arm will lower and either start moving towards the center of the record spindle automatically or it will sit and do nothing.If it moves automatically, adjust the diaphragm arm a little so it doesn't move.If it does nothing, check how close it is to begin moving by gently pushing the tonearm to the left.The sensor should detect that and begin to drive the arm forward to catch up.If it doesn't move at all then you need to adjust the diaphragm arm so it does.
This can be a very iterative process and takes some patience.I like to make my coarse adjustment so the arm lowers and very little nudging of the tonearm is needed to stimulate the tracking.That is the point where I move on to the actual service manual procedure and use the eccentric screw.
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 ;-).
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
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,
Good job.
BeoVision Haermony 65"...BeoLab 28 Anthracite....BeoLab 17 as REAR....BV10-32....BC6-26....Beosound 9000....Beosound 1 New York edt....Beogram 4002....Beoplay Emerge....Beoplay M5....Beoplay M3....Beoremote Halo....BeoRemote One BT....Beo6....Beo4....Beo4 Cinema....BeoLink 7000....Serene....H95 Black LTD....H9i Rimowa....6 x H6....Form 1....U70...
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: 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.
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.
Good clarification Martin.
John
Ok thanx for answer
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.
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
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