Beogram 4002 (5523): A New Arrival From Louisiana - First Impressions

I recently received a Beogram 4002 (Type 5523 with DC platter motor) from a customer in Louisiana. It arrived safely packaged in a Beolover double box, and no shipping damage occurred. This post gives a first assessment of the unit. I extracted the Beogram from the packaging and put it on my bench

As in most cases, the dust cover was fairly scratched up:

Luckily, this can be fixed with a nice shiny new reproduction hood and a new reproduction aluminum trim!

Under the hood, the unit has nice aluminum surfaces:

Like most, after almost 50 years, it has a few minor dings and blemishes:

There is a bit of damage around the platter cutout, possibly from carrying the unit around without tightening the transport locks:

On the positive, the platter is still very nice:

The plinth still has decent corners:

Unfortunately, there is a bit of damage on the right side

This could possibly be fixed, but my customer wanted the frame replaced with a new CNC-machined 4000c-style oak frame anyway.

The keypad seems to have had its coating removed:

It probably had a worn coating in the areas where fingers touched it, and removing all of it resulted in improved looks. This can be fixed with a new reproduction keypad plate. See here for more information about our keypad restoration service.

After this visual inspection, I removed the aluminum plates and the platter:

I found some 'well-known parts': A new Beolover Tracking Sensor LED Light Source (Beogram 4002 and 4004) and a new machined aluminum pulley had been installed at some point:

The DC platter motor had a non-spec pulley installed. This one has the wrong shape since it is cylindrical and lacks a crown that keeps the belt centered while the motor spins:

If I can successfully restore this motor, I will fit it with a properly crowned Beolover DC Platter Motor Pulley for Beogram 4002 and 4004.

As found in most, this Beogram 4002 had also completely lost its transport lock bushings:

This will be fixed with a set of Beolover Transport Lock Bushing Set for Beogram 4000, 4002, and 4004.'

At this point, I plugged the unit in and pressed START. The carriage came alive, and the platter motor started running with a shriek. A clear sign that its shaft bearings are in urgent need of reinfusion with oil under vacuum. The carriage found the LP setdown point and the solenoid engaged. All good lifesigns!

When I pressed STOP to return the carriage, there was no reaction. I had to use the ">" button to manually drive it back. This may indicate a dead transistor in the electronic switch, or a very oxidized switch terminal under the STOP key. We will see.

In summary, I think this Beogram 4002 is a good starting point for a restoration to like-new condition. Stay tuned for updates on this project!

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!

Beogram 4002 (5513): Restoration of the Platter Motor, PCBs, and RPM Panel

Recently, a customer in California sent me the DC platter motor, along with the PCBs and the keypad assembly, of a Beogram 4002 (Type 5513) for restoration. I was given the additional information that the Beogram would blow fuses whenever plugged in.

As usual, I began with the platter motor. The oil infusion of the bearings under vacuum can take up to 3 days, so it was the perfect starting point for this project. This shows the motor as received:

I took it apart to extract the shaft bearings:

The bearings are the two small donuts on the black pad upfront. I submerged them in synthetic oil and pulled a vacuum. Immediately, strong bubbling started:

The bubbling is indicative of air being drawn from the pores of the Oilite bearing material. As the air goes out, the oil goes in! When the bubbling stops, the bearings are replenished and can be used again. While this process was underway, I focused on the main PCB. This shows it in its as received condition:

Here is a detail shot of the 'RPM section' with the original Siemens RPM relay and the RPM trimmers:

Due to the 'blows the fuses' warning I was given, I installed the board in my bench 4002 to see what was going on. I hooked the board up to power using a bench supply instead of the Beogram transformer. This allows ramping up the voltage slowly while watching the current meter. Indeed, already at a voltage below one volt, the current of the bench supply was maxed out, and the current limiter prevented worse things from happening.

The culprit for the short circuit was found quickly: When I removed the screw that holds one of the two Darlington power transistors that are mounted on the solder side, it became apparent that the screw was missing its insulator sleeve and the mica sheet under the package was also absent:

The sleeve and mica sheet prevent contact between the collector of the transistor and ground (via the PCB mounting post that is used for heat dissipation from the transistor in this design). Without these insulators, there is a direct short circuit between the 21V power rail and ground, i.e., the fuses will blow immediately when the Beogram is plugged in. The other Darlington was also missing the bolt insulator:

Someone clearly did not appreciate Ohm's law!...;-).

While the board was still mounted, I replaced the two Darlingtons. This shows 1IC1, which regulates the 21V rail:

I usually replace the original TIP120s with their higher current cousin, TIP102. For some reason, modern TIP devices need some additional capacitance (the yellowish component in the above picture) at their emitters in this circuit configuration. Otherwise, they can develop a high-frequency oscillation superimposed on the 21V rail, which can fool the record detection circuit into believing there is no record on the platter. This subsequently disables the arm-lowering circuit even if there is a record on the platter.

This shows the new TIP107 that replaces the original TIP125 that serves as 1IC4 to control the arm-lowering solenoid:

Then I removed the board and inspected the component side. Immediately, I saw that one of the four H-bridge pnp transistor cans had been replaced with a non-spec type:

A closer look revealed it was a S9012, a pnp transistor rated for 500 mA collector current:

The original BC143 types are rated 1 A. 500 mA may work for some time if the carriage mechanism is in top shape and there is not much mechanical resistance. Then the carriage motor runs reliably below 500mA. 

I replaced all the electrolytic capacitors and the power transistors. This shows the restored board together with the extracted original components:

The Siemens relay was replaced with a Beolover Siemens Relay Replacement for Beogram 4000, 4002, and 4004, and the RPM trimmer received an upgrade with modern 25-turn precision encapsulated trimmers for more exact adjustment:

Next, I focused on the output PCB. This board had been modified by a previous owner of the Beogram:

The circuit on this board delays the output relay so it only opens after the needle has hit the groove:

I replaced the output relay and the electrolytic capacitor that determines the delay:

The picture below shows the RPM panel that is mounted above the keypad. It contains two incandescent bulbs that I usually replace with LEDs. The panel is shown flipped on its back, revealing the two bulb covers:

I removed the covers. This shows the bulbs still installed:

The two small green PCBs are the Beolover RPM Panel LED Backlights for Beogram 4002 and 4004 (Types 551x/552x). The boards are directly soldered to the terminals that connect the wires of the bulbs:

This shows one of the boards installed in detail:

The PCBs do not obstruct the bulb covers, which can be reinstalled after the boards are in place:

Next, I calibrated the DC bias of the sensor arm transistor (1TR3) to yield 4V at its collector:

Then I moved the bias trimmer to the component side:

Whenever work is done on the record detection circuit, it is a good idea to measure the sensor response. This oscilloscope trace was measured at the collector of 1TR3 with the sensor over the empty rotating platter:

Each dip corresponds to a platter rib passing under the sensor. The amplitude of the signal is about 6.3V, a perfect result. This record detection circuit is in good shape!

Meanwhile, after about 48 hrs the bubbling around the motor bearings had stopped. I extracted the bearings from the oil:

I reassembled the motor and installed all the components for testing in my bench Beogram 4002. I ran a 24-hour RPM stability test with the BeoloverRPM device:

The BeoloverRPM has two operational modes. In 'slow' mode, it measures the RPM in 10-second intervals and relays the measurement to a serial port of a computer. This allows graphing the RPM over long periods of time using Excel or similar software. This shows the result of a 24 hrs measurement:

This result is pretty much as good as it gets with the DC motor Beogram 4002. 

In the 'fast' mode, it transmits an RPM measurement every time a platter rib passes under the sensor. This yields high-resolution graphs that show short-term RPM changes ("wow and flutter") in detail. This graph shows a measurement covering about 35 turns of the platter, representing a run time of a little more than 1 min:

The zig-zag pattern is a measurement artifact that originates from small spacing variations between the platter ribs of my bench Beogram. All Beogram platters have such variations due to manufacturing imperfections. This generates a repeating pattern every 24 measurements (there are 24 ribs around the platter), which is superimposed on the real RPM changes that are introduced by the feedback system that keeps the motor RPM stable over time. This real RPM change is essentially the sine-wave-like pattern that modulates the zig-zag pattern. An evaluation of the wavy component yields a wow and flutter estimate of about 0.1%. This is 2x of the 0.05% stated in the specs list in the service manual.

    This difference is most likely systematic due to the entirely different way wow and flutter were measured in the 1970s when these Beograms were produced. Back then, the measurement was carried out with a 1 kHz tone on a test record. In these measurements, deviations from the 1kHz center were measured with an analog spectrum analyzer and then converted into a wow and flutter number. It should be pointed out that this discussion is pretty academic since humans typically start recognizing frequency fluctuations above the 0.7% threshold, i.e., the RPM fluctuations of this Beogram are well below this threshold, whether the number is 0.05% or 0.1%. This motor is definitely ready for duty again!

This concluded my work on the received parts, and I will soon send them back to my customer in California.