Beogram 4002: Restoration of DC Platter Motor

I recently received a Beogram 4002 DC platter motor from a customer in France for restoration. His Beogram had the usual randomly occurring RPM variations. Something that will most likely be fixed by re-infusing the dry motor shaft bearings with oil under vacuum. Most of these motors have bearings that lost all of their stored oil, and this causes the shaft friction to increase significantly.

This shows the motor as received:

I disassembled it to extract the shaft bearings:

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

The bubbling indicates that air is being drawn from the pores of the Oilite-bearing material. The leaving air is successively supplanted by oil in a diffusion process. The process has completed when the bubbling stops. In this case, this happened after about two days. At that point, I extracted the bearings from the vacuum chamber:

Then I reassembled the motor with a new Beolover DC Platter Motor Pulley for Beogram 4002 and 4004 and installed it in my bench Beogram 4002 for testing with the BeoloverRPM device:

The BeoloverRPM is able to log the RPM in 10s intervals into a serial port of a computer over long periods of time. This allows precise detection of intermittent RPM deviations that otherwise would be difficult to detect. This is the graph I measured after about 24 hrs:

This flat curve is 'as good as it gets' with Beogram DC platter motors! This motor is ready for duty again! It is time to send this motor home to France for another tour of duty in its Beogram 4002!

 

Beogram 4004 (5526): Upgrade With a New Beolover Carriage Motor and the Commander Remote Control System

I just sold a fully restored Beogram 4004 (Type 5526) that I offered via my store to a customer in California. Read here about the work done on this unit. My customer decided to get the unit upgraded with a new Beolover carriage motor and the Commander remote control.

The new carriage motors run much quieter than the original ones, and the Commander allows full control of all functions with an Apple remote. The Commander also adds auto-repeat functionality.

I put it on the bench and removed the aluminum panels. This shows the original motor still in place:

I extracted the motor, opened up the enclosure, and inserted the new Beolover carriage motor:

This shows the new motor installed:

Then I removed the keypad assembly to install the Commander remote control. Since this was a 4004, the Commander gets its power from the output PCB that is located under the keypad:

I plugged the Commander board into the keypad header on the main board and put the power breakout adapter into the keypad header on the output board. Then I connected the Commander with the white harness to the small jack on the breakout adapter: 

Here a detail shot of the power connection:

Then I plugged the keypad back in and bolted the autorepeat indicator in place with the main keypad mounting screw:

This concluded my work on the upgrades. Now I will play this Beogram a bit, and then it will be time to send it to its new owner.

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 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.