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Beogram 400x projects

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Søren Mexico
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Is it the relay or the damper cylinder that causes the delay 

Collecting Vintage B&O is not a hobby, its a lifestyle.

Søren Mexico
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sonavor:
I have the materials to fix the Beogram dust covers but so far I haven't done one. I need to go ahead and learn the technique. I even have a badly damaged one I can practice on so I don't really have an excuse not to.

I have done several covers and the only way to go is like I did with my BG 1000 cover

While I had all the sanding utensils out and ready, I started on the ugly acrylic cover, I placed it on a sturdy cardboard box that nearly fit into the cover Bad idea as I sanded with 30 micron the cardboard damaged the inside of the cover, I had to cover the box with a cotton rag, and later sand the inside with 15 micron and so on), I then wet sanded with a 30 micron sheet, parallel to the long side until the deep scratches was gone, the most difficult was the damage you can see in the first pics. I then went to 15 micron sanding parallel  to the short side until all the grains from the 30 micron was gone, then down to 9 micron, long side, until all then grain from 15 micron was gone, then down to 3 micron, short side, I now had like a haze on the acrylic, not quite clear, I then took to Novus No. 2 scratch remover, and that did it. With 25°C in the garage this was a boot camp, 2 hours hard work, sweating like after a 5 Km run. I have some more covers where I tried with Novus No. 3 and 2 and 1, It didnt turn out as well as this one.

The Novus system is only good for very fine scratches

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sonavor
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sonavor replied on Thu, Jan 21 2016 5:14 AM

Søren Mexico:

sonavor:
I have the materials to fix the Beogram dust covers but so far I haven't done one. I need to go ahead and learn the technique. I even have a badly damaged one I can practice on so I don't really have an excuse not to.

With 25°C in the garage this was a boot camp, 2 hours hard work, sweating like after a 5 Km run.



Now I remember why I put off doing the dust cover restoration Smile

sonavor
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Søren Mexico:

Is it the relay or the damper cylinder that causes the delay 

I am pretty sure it is the solenoid but I have been readjusting the valve on the damper and the more I exercised the tonearm the faster the solenoid started operating. Right now it is activating immediately.

The thing I am not sure about are the voltages across the solenoid. The DC voltage on each lead to ground when the Beogram is plugged in and in the OFF state is 49 VDC. When I press ON the tonearm starts to move and the voltages on each solenoid lead to ground goes to 41V. Then when the set down point is reached, one solenoid lead drops to 36V and the other to 39V.

Here is the solenoid circuit. Ǭ₁ is the controlling signal from the logic board.


Søren Mexico
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My tonearm came down very slowly, but that was due to old grease in the tonearm mech. it also stayed down because of it. my solenoid acted immediately where it should

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Søren Mexico
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I will check voltages when I get mine working again

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sonavor
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sonavor replied on Thu, Jan 21 2016 3:02 PM

Later today I am going to put my working Beogram 4000 back on the bench and measure the solenoid circuit operation on it to compare.

sonavor
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Here is Beogram 4000 #1 back on the bench for some solenoid voltage measurements. I used a pair of DVMs at first to measure each solenoid lead.

Important Note: There is 30V to 40V power on those pins as soon as the Beogram is plugged in. So just because the turntable is in the OFF position doesn't mean there isn't power on various areas of the circuit. That is true for a lot of equipment but is easy to forget when on the trail of repairing a problem.

On this first Beogram 4000 turntable I have a little over 30 VDC on the solenoid terminals when the turntable is OFF. That is down from the 49 VDC my second Beogram 4000 turntable has.


sonavor
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I switched the measurement device to my oscilloscope so I could watch what happens to the voltages when the tonearm lowers and raises. Here is the scope measuring the Beogram in the OFF position.


sonavor
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Setting the scope trigger to catch a single event I captured both solenoid signals when the tonearm lowers. So other than the voltage levels being higher, the behavior of the solenoid circuit appears pretty similar to what I saw on the second Beogram 4000. Now I can go back and watch that turntable's solenoid action with the scope to compare.


sonavor
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sonavor replied on Thu, Jan 21 2016 8:03 PM

The oscilloscope picture shows the results when the arm lowering event occurs. At that point 0TR4 turns on and the normally closed current limit switch drops the solenoid lead (monitored on scope probe 2) to ground. That also pulls down the other solenoid lead voltage slightly. It takes about 11milliseconds for the mechanics of the solenoid to complete which opens the current limit switch so the 8.2 ohms load resistor takes over instead of a direct path to ground. That raises the probe 2 solenoid signal to an idling level about 3V less than the other end of the solenoid and keeps the solenoid engaged but drawing less current across the solenoid.

My second BG4000 turntable went from not working to working slow (taking 30 seconds to engage) to working normally yesterday. One issue was the current limiting switch. A second was repairing the control logic cause by the probe mishap. I am guessing that exercising the solenoid finally brought it back where it is working fairly well but I am also wondering if there is a problem with the control transistor 0TR4. There could also be an issue with one of the transistors that control 0TR4 (1TR10 and 1TR11).

I will know more after I get a scope picture of the Beogram 4000 #2 unit. I may decide to replace 0TR4.

sonavor
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Before measuring the second Beogram 4000 with my scope I took apart the solenoid circuit (PCB 6) to check solder joints and components. The main switching transistor is 0TR4 (TIP41A) which is mounting nearby on the Beogram chassis. When I pulled it out and tested it, I discovered it measured kind of odd. Sometimes my PEAK transistor tester measured it good, other times it couldn't detect it. To be sure, I used a second PEAK transistor tester and it did the same thing. That type of measurement problem doesn't happen with my new TIP41A transistor samples. So I suspect this device might have been the problem with the delayed solenoid switching problem. In any case I don't trust putting the original transistor back in. This isn't the easiest component to install.


sonavor
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Here is the new 0TR4 (TIP41A) transistor installed. I also replaced the mica insulator. The new one is easier to see as it is tinted. There is a small, plastic insulating insert for the mounting hole in the transistor. Care must be take to make sure the mounting screw doesn't contact the metal mounting tab which is part of the collector. I double checked that there is not connection between the mounting screw and the collector with my DMM after installing it. I also double checked tracing the wires from all three transistor leads back to their destinations, verifying with the schematic. Everything looked correct.


sonavor
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While I had PCB 6 unbolted from the tonearm transport I reflowed the solder joints and made sure all of the wires were good. This picture shows the Beogram ready to measure the solenoid voltages with my oscilloscope.


sonavor
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The other day when I was looking at these solenoid voltages, then the same voltages on my first Beogram, I was wondering why the OFF condition voltages were so different. The first BG4000 measures around 32VDC at rest (OFF) and this second BG4000 measured around 49VDC.

Yesterday I finally realized that this second Beogram still has the original transformer and voltage selector switch. The switch was set to 110 VAC so I changed it to the 130 VAC position. My local house voltage measures close to 125 VAC so 130 is a better choice. The first BG4000 turntable has the replacement, toroid transformer that is fixed at 120 VAC.

Now the solenoid voltages of the second Beogram measure lower at rest (41 VAC).


sonavor
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Here is the second Beogram 4000 now during operation. The solenoid voltages look like the first Beogram and the arm lowering is working like it should.


sonavor
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The Beogram functional logic and basic operations all appear to be working now. It scans for an LP and returns when it can't find one. It will detect a 17cm record, change speed to 45RPM and set the tonearm down correctly.

I think all of the repair steps are done. Everything electrical and mechanical appear to be fixed. The next step is to set the turntable up for use by going through all of the service manual adjustment procedures and rechecking electrical adjustments (trimmers). This means calibrating the tonearm tracking force, platter height, forward/reverse speed, tonearm groove tracking, motor speeds and platter centering. I will also need to do some rework on the wood trim to make it look good again. There is some fading on the front trim.


sonavor
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I left out a picture of the underside of PCB6 where 6D1 and 6C1 components are mounted. Just in case anyone was wondering. Smile
I had my able lab assistant, John, hold the board up for the picture.


sonavor
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This week I started on the service manual mechanical adjustments. The first thing I want to do is get the platter bearing adjusted so the platter sits true and the distance from the platter surface to the top of the detector arm is 23mm. This adjustment can take quite a while as there is a lot of trial and error in getting everything adjusted. It is also slow going because you have to remove the platter and sub-platter between each adjustment.

It is best to watch video of these adjustments as still photos don't demonstrate the process very well. Beolover produced two good videos on the adjustment.  There is one video for the Beogram 4000 (like my first one) and one for the Beogram 4002. However, this second Beogram 4000 has the platter bearing mounts like I have in my Beogram 4002 turntables so the second video applies to this Beogram.

Here are my two different platter bearings.


sonavor
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This second Beogram 4000 is turning out to be quite a challenge in getting the platter level along with the correct platter height. When I got close to the platter surface to detector arm top measurement of 23mm (at three triangular measurements on the platter), the platter ended up being too low. It would scrape the top of the strobe lamp housing. The platter would have also been way below the Beogram deck trim.

In checking the detector arm between my first BG4000 turntable and this one I can see that the detector arm is not level. The first one isn't perfectly level either but is way better than this new one.


sonavor
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I tried to improve the detector arm position by going through and adjusting the floating chassis to be as level with the Beogram base as I could. Then, with the base level to my table, I rechecked the detector arm level. It is still tilting down too low.


sonavor
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The floating chassis, in the same direction as the detector arm is oriented (back to front), does not measure perfectly in the center when compared to the level of the base. The floating chassis leaf springs affect that measurement but I feel I have the springs adjusted as well as I can. Interestingly, the same level measurement on two different locations of the floating chassis don't measure the same. They are close but the bubble is at opposite ends of the center range.


Søren Mexico
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Without the sub and top platter the the floating chassis will not hang free and correctly suspended

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Søren Mexico
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There are no machined surfaces on the floating chassis, so the level vill be different where ever you put you level, concentrate on the level of the detector arm and that the base chassis is standing level, and check the level of the carriage shafts

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sonavor
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sonavor replied on Wed, Jan 27 2016 7:48 AM

Søren Mexico:

Without the sub and top platter the the floating chassis will not hang free and correctly suspended

I agree, the actual height of the platter to the turntable deck will have to be adjusted with the leaf springs at the end. But for the purpose of getting the platter bearing level and the height set relative to the detector arm I need to have the chassis level...which I believe it is. At least as level as I can get it.

The problem is, the detector arm doesn't hang level. It is also mounted to the floating chassis so it should be level with the floating chassis. Because the arm isn't level, the 23mm check to the platter deck measurement can't be made accurately.

I don't see a good way to fix the detector arm level yet.

sonavor
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I looked at the service manual procedure again -


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sonavor replied on Wed, Jan 27 2016 8:00 AM

I did the first part with the suspension floating. In the second part of the adjustment it says to adjust the tilt and height (again) with the chassis locked. I will try that next and see if it helps my measurement.

One work around might be to temporarily adjust the tonearm so it is perfectly level with the platter and make the 23mm adjustment of the platter bearing to the tonearm. After that is adjusted I can match the top of the tonearm back with the detector arm and then compensate for it not being truly level when I set the limit of the tonearm drop (0.5mm from the top of the first rib).

Søren Mexico
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I would just check the level of the surface the deck is standing on, then the 13 mm detector arm to the platter, then without locking the transport screws level the platter to the deck cover plate (level and center) with the blade springs, and last the tonearm to the platter. There is no need to use water levels except for checking your workbench

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chartz
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chartz replied on Wed, Jan 27 2016 3:59 PM

I could never adjust mine exactly as per service manual instructions. I've tried everything to no avail. The headroom at the upper left spring is insufficient to obtain the full floating of the suspended chassis. 

At one time, when the carriage was near the LP label, the chassis was not suspended on the left side.

Same series as yours.

John, should you find a solution to this, I'd be glad to have it.

 

Jacques

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sonavor replied on Wed, Jan 27 2016 4:04 PM

Søren Mexico:

I would just check the level of the surface the deck is standing on, then the 13 mm detector arm to the platter, then without locking the transport screws level the platter to the deck cover plate (level and center) with the blade springs, and last the tonearm to the platter. There is no need to use water levels except for checking your workbench

I kind of went round trip and did that late last night. The levels though were just for another way for me to check how my different surfaces were relating to each other.

Where I left it, late, late last night was I reset the platter bearing to a good starting height and got the platter level with the chassis locked down. While doing that I also reset the leaf springs all to the same amount.
Next I unlocked the chassis and checked where the platter was in relation to turntable deck when it was installed. As expected some adjustment to the leaf springs was needed to get the platter surface parallel to the deck top. I didn't worry about the platter and deck being flush at this point. I just wanted them parallel.

After I achieved that I checked how far above the deck the platter was. It needed to come down about 2.5mm. So I adjusted the platter bearing down by that amount and then the platter was pretty flush with the deck.

Now for the platter height to the tonearm or detector arm. Since the detector arm has too much tilt I didn't us it. I temporarily changed the tonearm height setting so I could measure it level with respect to the platter. Then I measured the distance from the top of the tonearm to the surface of the platter at three points (near the edge of the platter, near the center of the platter and towards the back of the arm). They all three measured the same (around 24mm). So the distance is higher than required.

sonavor
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sonavor replied on Wed, Jan 27 2016 4:09 PM

chartz:

I could never adjust mine exactly as per service manual instructions. I've tried everything to no avail. The headroom at the upper left spring is insufficient to obtain the full floating of the suspended chassis. 

At one time, when the carriage was near the LP label, the chassis was not suspended on the left side.

Same series as yours.

John, should you find a solution to this, I'd be glad to have it.



Yes Jacques,

It looks like I will now have to raise the platter bearing 1mm to meet the 23mm for the arm height to the platter. This will cause the platter to not be flush with the deck and like your Beogram, I don't think the leaf springs on this one can compensate for it. I have completely reset and gone through getting the three leaf springs adjusted where the floating chassis is floating well and I have some play in compensating for the platter. It is rather difficult to get adjusted. My first Beogram 4000 unit was able to get everything aligned. I may have to live with the slight imperfection in this one.

sonavor
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Thinking about this some more...
Jacques, the problem may lie in the position of the chassis lock down points. When adjusting the floating chassis suspension springs, the travel limits are dictated by the movement within the play of the unlocked chassis lock down assemblies. Can those positions be adjusted up or down? I haven't ever taken those apart yet. Maybe that is a question for Beolover as he as disassembled those before. If the centering position of the lockdown assembly can be adjusted up or down that might fix the problem.


sonavor
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I removed the chassis lock downs for the Beogram to compare them. The left and right rear locks had pretty much the same distance where the mounting nut was threaded onto the bolt (at the bottom of the assembly). The front down, where the leaf spring won't adjust as well, had the mounting nut threaded much further onto the bolt (at the bottom of the assembly).  I believe that is affecting the range of my adjustments with the floating suspension.


sonavor
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For the detector arm not being level with the floating chassis, I found out there are set screws for the tonearm carriage rails that control their height. The screws are not easily accessible to make the adjustment though.


sonavor
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Testing changing the rail position shows it does affect the detector (and tonearm) relative position to the floating chassis (and platter). I would like to raise the front rail slightly and lower the back rail to get back as much of the detector arm tilt I can. I might be able to get 2mm out of it.


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It is quite a job to remove the floating chassis to get to the underside of the set screws for the rails. I decided to do it anyway being careful of all the wires and not to force anything. It looks like only the rear set screws can be adjusted. The front screws are flush, don't have adjustment slots and appear to be glued in.


sonavor
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Deciding to go ahead with this chassis adjustment rework required me removing the lockdowns, leaf springs and floating chassis. While everything is out I figured I might as well take a couple pictures as I usually don't strip the Beogram down this far.
Here is the floating chassis removed.


sonavor
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Here is the turntable with the floating chassis out of the way.


sonavor
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My goal in reworking this suspension system is to get back any missing travel available in the platter height relative to the turntable deck. In addition I am removing the set screws for the back tonearm rail to lower it and hopefully help correct the arm downward tilt. I am also cleaning and making sure the suspension leaf springs are all adjusted to the same starting point.

I think the biggest gain will be in reworking the chassis lockdown assemblies. Earlier I discovered that the front assembly was unbalanced inside where the lockdown bolt moves the two locking nuts. In the reassembly I am making sure the bolt just threads onto the bottom nut. That will be my starting position for the lockdown screws on all of the nuts.


sonavor
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I'm sure there are several good ways of assembling these lockdown assemblies. Because I have the floating chassis removed, I was able to visually make sure the tightening bolt was inserted the same amount in the top and bottom nuts. Beolover has a good video that shows how to work on the lockdown assembly when the floating chassis is not removed. It if for a BG4002/4004 model turntable but the task is the same.


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