Beogram 8002 (5633): Finishing Up - Reattachment of Aluminum Panels and a New Dust Cover with Transferred Original Trim

I recently completed the functional restoration of a Beogram 8002 from a customer in Missouri. A few days ago, I received the new dust cover back from Beomazed, who performed his magic to transfer the original 'Beogram 8002' labeled trim to a new pristine reproduction dust cover. Since the Beogram had played flawlessly while the dust cover was getting done, it was time to complete the unit and put everything back together.

Here is an impression of the final result:

Looks pretty close to new! Beolovely!

To get there, I first glued the loose main aluminum panels back into place. The double-sided tape that was used to attach the panels is degraded in most cases. I usually remove the tape remnants by placing pieces of isopropyl alcohol-wetted paper towel on the degraded tape. After a 1 hr soak, the stuff can usually be rubbed off.

I usually use epoxy and some M3 washers to glue the main plate back into its place:

Once washers and epoxy are in place, I carefully adjust the plate and clamp/weigh it down:

For the small plate I used double sided tape:

Usually, the steel plate that is attached to the black panel under the arms also comes loose:

I usually use double-sided tape for this one, too:

The next steps were putting the Beogram back into its enclosure and installing the new reproduction hood with the transferred original trim. Then it was time for a test spin. I selected one of my favorite David Bowie albums, ChangesOneBowie (RCA Victor APL1-1732), a great compilation that was released in 1976. Here is an impression of this lovely album playing on this like-new Beogram 8002:

After this test, I carried the Beogram to my photo studio and took a nice set of pictures.

Enjoy!:

Beogram 8002: Skipping and Jerky Run-Off Carriage Motion - Installation and Test of a New Beolover Carriage Motor

It is good that I always listen to a restored Beogram for a while before I send it out. Some issues can only be detected after a longer period of use since they are intermittent or subtle. This also applied to the Beogram 8002 (Type 5633) that I recently sold to a customer in the UK. While I played it, I realized that the pickup occasionally skipped on records that I knew were perfectly fine. This only happened on a few sides that I played. But it indicated that something was wrong.

I encountered a similar issue a while back, where I resorted to tweaking the H-bridge gain to give the motor a bit more power. The reason for such behavior is increasing friction in the motor or elsewhere in the carriage mechanism, causing 'sticktion' where the motor does not get enough power to overcome static friction, while the arm moves inward on the record. After a few more turns of the record, the tracking sensor is finally at a point where the voltage at the carriage motor is high enough to overcome the stuck mechanism, and the motor suddenly starts running at a high speed so the carriage can catch up with the arm. This rapid catching-up process can cause sufficient mechanical turbulence that the very light tonearm skips a groove.

In this case, there was yet another indication that the motor had an issue: During runoff, the carriage moved in a few big jerky steps instead of a smooth, quick motion tracking the needle as the runoff groove drags it towards the center of the record until auto-return is triggered.

This time I thought, why not see if one can replace the Beogram 8002/8000 carriage motors with the Beolover Carriage Motor for Beogram 4000, 4002, and 4004. A quick measurement on the motor terminals indicated that the motors in the 8002 run at similar voltages to the motors in the 400x.

This shows the open carriage motor compartment of the 8002:

First, I unsoldered the brown lead and connected my multimeter in current measurement mode between the wire and the motor terminal. Then I operated the turntable to see what the maximum current might be that this motor draws:

As expected, the motor draws the most current (~70 mA) during the carriage return after pressing STOP.

I removed the motor:

This shows the original motor in comparison to the Beolover motor:

The new motor is a bit smaller. Like most new designs, it is more efficient than the original motors due to better magnets and better manufacturing techniques available today.

Due to the size difference, I had to design an adapter to make the new motor fit into the original motor housing. This is what I came up with:

I 3D-printed two plastic clam shells to increase the diameter and length of the motor to match the original form factor. The additional two EPDM rubber rings serve as vibration insulation. They are put on the motor like this:

Then the plastic pieces are fitted around the motor:

The plastic pieces have two protrusions that hold the motor in place and prevent it from sliding inside the housing:

The new motors have a small round mark next to one of the terminals. The brown wire needs to be connected where the mark is, and the blue one goes to the other terminal.

I soldered the blue wire:

Then I did another current measurement between the brown wire end and the unconnected motor terminal:

Like the original motor, this motor drew the largest current during carriage return. At 50 mA, it is about 30% smaller than the value of the original motor. This was to be expected. In the Beogram 400x series of turntables, I saw a similar power reduction for the same performance. Some things get better as time marches on!...;-). Lower power is always preferable. It reduces the stress on the H-bridge components and also results in a quieter and lower vibration operation. After this test, I connected the brown wire. Since it is shorter, I had to put in a wire bridge to extend it to the motor terminal:

The cover still fits perfectly:

This is how it looks from the front:

After this installation, I listened to a few records with the new motor, and everything worked very nicely. I noticed how much more quietly the motor operated during <</>> and START and STOP operations. Significantly fewer vibrations compared to the original motor! Beolovely!

At that point, I realized that it would be nice to get some oscilloscope shots of the tracking signal on the motor terminals. So I opened the motor housing again and connected my oscilloscope between the motor terminals. This trace gives a nice summary of the motor operation. It essentially captures the voltage fluctuations during the last few turns of the record before the 'run off' groove, then the signal during run off until auto-return is triggered, followed by the actual return:

I wanted to compare this signal with the original motor, and so I installed the original motor for another measurement. This shows the same operational sequence as above:

While the overall pattern looks similar, there are notable differences: The voltage jumps during regular tracking are larger for the original motor. They also have a higher baseline. This indicates that the tracking sensor needs to send more voltage before the motor moves. Secondly, the run-off signal confirms what I observed visually, that the carriage makes bigger jumps. Comparison to the new motor shows that the original motor moves in 3-4 big steps, while the new motor gets a much larger number of voltage pulses, causing it to move the carriage much more smoothly.

In summary, I think the Beolover carriage motor is an excellent substitute for the original motors, which seem to be on the verge to develop age related issues. If you are interested in upgrading your Beogram 8002 or 8000 with a new carriage motor, it is now available via the Beolover's DKaudiolover store!

Beogram 8002: Transformer Block - A Comparison Between 120V and 240V Versions

I just sold a Beogram 8002 (Type 5633) that I recently restored to a customer in the UK. Unfortunately, the Beogram was a 120V US version. This meant it came with a transformer block specifically designed for the US power grid, which offers 120V at a grid frequency of 60Hz.

The Beogram 8002 (and 8000) were designed in a way that they could be converted for different power grids by simply swapping out the transformer block. This enabled B&O to use the same hardware globally with only the transformers adapted to local requirements.

So before sending this Beogram to the UK, I wanted to convert it to 240V/50Hz so that my customer could directly plug it in without needing an external voltage transformer. 

It is interesting to note that while the external transformer approach works well with most devices, the Beogram 8002/8000 have a design quirk that makes this approach less than perfect: They use grid frequency AC to run the linear 2-phase AC motor that drives the platter. Since the second phase is shifted relative to the first using a phase capacitor, the capacitor value is specific to the AC frequency used. This means that when a US 120V/60Hz Beogram is hooked up in the UK via a 240-to-120V grid voltage transformer, it sees the proper 120V, but it gets only 50 Hz. This means its factory phase capacitor does not have the proper value. This is the reason why B&O put this phase capacitor into the transformer block, so it would match the specific grid frequency the block is specified for.

I was able to buy a 240V/50Hz UK transformer block from a fellow Beolover in the UK. When I received it, I decided to explore the differences between the 240V and the original 120V blocks. Most importantly, I wanted to measure the voltages of the secondary windings of the two blocks to make sure I could swap them without issues. I had never done this before, so caution was on order!...;-).

This shows the original 120V/60Hz block:

And opened up:

The big can is the phase capacitor for the motor. It has a 27uF value optimized for 60 Hz. The fuse is a 300mA slow-blow type:

I had the fantasy that one might be able to convert 120V blocks into 240V types by changing the primary winding connections, but a look at the wiring of the primary side suggests this is not possible. This shows the primary connections:

Each winding has a solid colored and a transparent wire coming out. On the top side of the terminal board, the transparent wires are connected via a solder terminal:

The grey and black wires go into the power cable (the black one via the fuse). This means the two coils are connected in series. Since the turns ratio formula for transformers states that the ratio between the primary and secondary voltages (Vp/Vs) is equal to the ratio between the number of windings on the primary and secondary sides (Np/Ns):

Vp​/Vs​​=Np​/Ns.

​This means the lower voltage bloc should have the windings connected in parallel, and the higher voltage bloc in series if conversion would be possible. This is how the grid-voltage-switchable earlier Beogram 400x do it. Their voltage switch basically re-arranges the way the primary coils are connected to adapt the number of windings on the primary side so that voltages between 100 and 240V can yield the same secondary side voltages.

Anyway, lets have a look at the 240/60Hz block that I just received:

This shows it opened up:

There are small differences to the 120V version: The phase capacitor is a bit longer, hinting at a larger capacitance, and the terminal plate looks different:

The first thing to note is that the fuse is a 160mA slow-blow type, i.e., has about half the current capacity of the 120V fuse. This makes sense since the same hardware is powered, i.e., the current on the secondary side is the same. Since the primary voltage is double, the primary current will only be half for the same power (P=V*I). 

A look under the plate reveals that the primary windings are connected in exactly the same way as in the 120V block:

The transparent wires are again connected in a series configuration. This means the 240V transformer indeed has a different design than the 120V version. It has different winding counts on the primary coils.

The phase capacitor indeed has a larger value, 39uF:

After this inspection of the two transformer blocks, I set out to measure the voltages that they produce on their secondaries when plugged into the specified mains voltage. For powering the 240V version, I used my big old 0-250V variac 

I measured peak-to-peak (Vpp) voltages with my oscilloscope. Here is an example of how I connected my probes (to measure the coils for the ±15V rails):

This is what I saw on the scope:

I made this table after I measured all secondaries on both blocks:

The calculated ratios are about ±10% around 1, which is 'good enough' considering the circuit design. Since there can be significant grid voltage fluctuations, the power supply of the Beogram 8002/8000 is pretty forgiving regarding the secondary voltages it expects to make the stabilized 5V and ±15V rails.

After this measurement, I felt confident that I could plug this 240V transformer block into the Beogram and give it a spin! But before I did that, I updated the phase capacitor with a Beolover Motor Capacitor for Beogram 8000 and 8002:

Note that for my initial test, I connected the 27uF capacitance for 60Hz grid frequency as shown above. My variac only changes the grid voltage but not the frequency. Ah, physics!...;-)

After installing the new phase capacitor, I plugged the 240V transformer block into the header on the main PCB of the Beogram and plugged it into the variac. Then I ramped the voltage to 240V, and the Beogram showed the usual red dot in the display! I pressed START, and it ran like before! Beolovely!

Of course, I was curious if the platter motor of this unit would still run properly if the 39uF/50Hz capacitance were used for the motor while running at 60Hz. Sort of a test of "can one use a standard grid 120V/240V transformer in a pinch if there is no proper transformer block available?".

I changed the capacitor setup to 39uF/50Hz:

I reinstalled the block and plugged it back into the variac. Then I pressed START. And everything seemed to work properly. The platter ran as usual, and the Beogram was able to lock onto "33.33" on the display, which means the microcontroller was measuring the proper speed and had no trouble maintaining it.

I played a few records, and it seems there is no practical penalty for using the 'wrong' phase capacitance.

So why use different capacitors for 50 and 60 Hz in the first place? I think it comes down to 'efficiency'. If the phase shift between the two motor coils is a bit off the optimal value, the motor consumes a little more current since it is less efficient. This does not matter much in this design since the RPM is feedback-controlled. So the control circuit simply compensates by giving the motor a bit more power to get the specified RPM.

I will now play this Beogram a bit more, and then it will be time to send it to its new owner in the UK!