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Beogram 4002: Restoration of DC Motor Video Published - Check It Out!

By popular request (really, I got quite a few emails about this!...;-), I finally completed my Beogram DC motor restoration video! It demon...

Tuesday, July 7, 2020

Beogram 4002 (5513): Completing the Restoration

In summer 2019 I restored the DC platter motor of a Beogram 4002 located in Virginia. Recently, I received the entire unit for an overhaul. The restoration of the arm lowering mechanism had already been done, and I found it in good condition. So I focused one the remaining aspects of the restoration.

I began by restoring the main PCB. This shows it in its original condition:
I replaced all electrolytic capacitors and installed a new RPM relay as well as new 25 turn RPM trimmers:
My next focus was the record detection circuit. I now always replace TR4, the transistor that is responsible for amplifying the sensor signal, with a modern high-gain type (2N5089; Newark 33C8280) since in several recent restoration projects I found this transistor to be out of spec, usually with a too low gain. And this is dangerous for the needle, since the record detection circuit goes 'blind' if this transistor stops amplifying properly. This shows the original TR4, a BC183C:
I replaced it and also installed a 25 turn 5 MOhm trimmer as bias resistor. The circuit is pretty basic, and uses only one resistor between collector and base for biasing the base. When installing this trimmer, it is necessary to put it first on the solder side of the board that one can adjust it with a plugged in board:
The manual prescribes a collector voltage of 4V. After adjusting the voltage, I installed the trimmer next to the new transistor on the component side:
And that concluded the restoration of the main PCB:
The next step was to replace the main dual capacitance reservoir capacitor with two modern single capacitors held in place by a 3D printed fixture:
Then I took out the keypad to get to the output PCB:
Here I replaced the output relay and the capacitor that defines the time constant of the relay action. I also added a (red) switch that allows connecting system and signal grounds in case there are hum issues:
While the keypad was out, I also removed the RPM trimmer panel to replace the light bulbs with LED boards. this shows the panel with the original light bulbs installed:
and here with my plug-in ready LED boards
This shows the panel in action:
The LED boards are based on red-green LEDs that are tuned to give an incandescent glow. The red component ensures that the red indicators are properly illuminated. If one uses orange LEDs, the indicators appear grayish, since orange LEDs do not emit red photons.

My next focus was the replacement of the light bulb in the tracking sensor. The picture shows the original black bulb housing in place:
This shows my replacement part in comparison to the original assembly:
The LED is in the same place as the filament of the original light bulb. This shows the LED assembly installed during the calibration procedure of the tracking feedback:
The blue trimmer is very convenient for fine-tuning the tracking feedback by adjusting the light intensity of the LED.
This Beogram still had the original plastic pulley, that are prone to crack and fall off:
I replaced it with a precision turned aluminum pulley that was supplied by another B&O enthusiast from Vienna:
Looks awesome! If you wanted one for your Beogram, I'd be happy to get you in touch with the source. Just send me an email or use the contact form on the right.

Another often degraded plastic part in this Beogram 4002 vintage are the transport lock bushings. If they look 'orangish', chances are that they are crumbling. This Beogram was no different:
I removed all three:
And replaced them with SLS printed nylon bushings that come in two parts, one to be inserted from the bottom
And one from the top:
This shows the one on the left side installed:
And with the top retaining plate bolted back in:
After rebuilding the transport locks, I went after the last remaining incandescent bulbs of this Beogram, the one in the sensor arm:
I usually replace them with an LED circuit on a flex-PCB that folds into the small bulb compartment, and that draws a current similar to the original bulb. This current tells the circuit that indeed a light source is in operation. This shows the assembly installed:
The LED is a 'warm-white' LED that has a red emission component that preserves the natural look of the B&O logo at the end of the sensor arm:
Whenever replacing the light source in the sensor arm, it is advised to check the sensor signal at the collector of TR4:
The signal needs to go all the way down to 0V and have an amplitude larger than 5V. This sensor circuit fully matches these requirements, and therefore is good to go.
The remaining tasks were to replace the old corroded DIN5 plug
with a new all-metal gold plated type:
And to do the adjustments. The first step is usually to balance the sub-chassis, adjust the platter height and the arm distance. Then the arm adjustments need to be made.

Before calibrating the tracking weight I replaced the circlip that holds the counterweight adjustment screw in place with a M3 nut and a washer:
This allows locking the calibration in place after the tracking force is properly adjusted:
Another important adjustment is the arm lowering limit:
This is the last resort protection for the needle if the record detection circuit would ever fail and allow the arm to be lowered on a rotating empty platter. The limit needs to be adjusted that the needle misses the lower areas of the black platter ribs. These lower areas are strategically placed where the set-down points for 12", 10" and 7" records are.
Finally, I adjusted the RPM with the BeoloverRPM device:
And then it was time to take this restored Beogram for a first test spin. I selected a recently acquired vintage record by Ramsey Lewis, "Tequila Mockingbird", which he recorded in 1977 on Columbia Records (JC 35018). I love the inner sleeve where Mr. Lewis shows off his braces...ahh the 70s!!...;-):
It is rapidly becoming one of my favorite 'easy listening' records. Perfect for an afternoon while restoring a Beogram! Of course this record was ultrasonically cleaned with a CleanerVinyl Pro Ultimate Kit on an Elmasonic P60H dual-frequency cleaner prior to listening. It now sounds pretty much like a newly pressed record. Beolovely!
I will now play this Beogram for a few more days and if nothing else comes up, it is time that it travels back to Virginia!

Friday, July 3, 2020

Beogram 4002 DC Platter Motor Restoration

I restored another Beogram 4002 DC platter motor for a returning customer. I guess one Beogram is just not enough for a real B&O aficionado!..;-). This shows the motor:
It made the typical dry bearing noises when I bench tested it. I took it apart to get to the bearings:
The bearings are the two small donuts on the black pad. I immersed them in motor oil and pulled a vacuum. Immediately vigorous bubbling started indicating 'thirsty' Oilite bearing material:
After about 2 days the bubbling stopped and I extracted the replenished bearings from the oil:
I put the motor back together and installed it in one of my Beogram 4002s for a 24 hrs RPM stability test with my BeoloverRPM device:
The BeoloverRPM allows logging the RPM in 10s intervals for long periods of time. Perfect for detecting intermittent RPM issues. This is the curve I measured for this motor:
This is pretty much as good as it gets with the DC platter motor! Time to send this motor to its new Beogram home!

Tuesday, June 30, 2020

Beogram 4002 Type 5513: Houston Beogram #3 Ready for Action Again

The part of the Beogram 4002 restoration I like the most has arrived. All of the tasks are complete except one final series of fun record playing tests in my office. I like to hook the Beogram up to one of my favorite systems and listen to records while I work at my desk. It is so much more enjoyable than watching television....and someone has to do this job ;-).

I am really pleased with this Beogram. There is something wonderful about knowing that this turntable has had a thorough going over.  It is all clean inside.  Beolover did a great job of restoring the platter motor.  There is comfort knowing that all of the control signals have been checked and adjusted to be at the correct levels. 

We didn't do a full cosmetic restoration like on some Beogram units. This one is in decent shape. At some future date the owner might want to invest in a dust cover polishing and a new coating on the control button panel. But for now it is looks great and is performing like a Beogram 4002 should.

Beogram 4002 DC Platter Motor Restoration

A Beogram 4002 DC platter motor recently arrived from Washington State for a restoration. This shows the motor as received:
After a quick bench test for life signs, which yielded the typical rough running noise caused by dry bearings, I took the motor apart to get to the bearings:
the bearings are the two small donuts on the black pad up front. I immersed them in motor oil and pulled a vacuum:
Immediately, vigorous bubbling started from the bearings, indicating that air was drawn from the porous Oilite brass bearing material into the vacuum. This air extraction makes room for oil inter diffusion into the material. This is how Oilite bearings provide lubricant to the shaft. But over time the oil gets depleted, and then it is time to replenish it. After about 72 hours the bubbling stopped, which means that the pores are filled again. I extracted the bearings:
and reassembled the motor to give it a RPM stability test in one of my 4002s with the BeoloverRPM device, which allows logging the RPM in 10s intervals over extended periods of time. Ideal for detection of sporadic RPM variations:
This is the curve I measured over about 24 hrs:
This is as good as it gets with the Beogram 4002 DC motors. Time to send this motor back to Washington State!

Sunday, June 28, 2020

Beogram 4002 Type 5513: Service Manual Checks and Sensor Adjustment for the Third Beogram from Houston

Today I moved the Beogram 4002 from the work bench to the test bench.
This project is heading into the final stretch of restoration tasks.

I went through service manual checks (and adjustments) as well as adjusting the three main sensors in the Beogram: The record detection sensor, the arm position sensor and the tracking sensor.

For the record detection sensor I followed Beolover's instructional video. I had already installed the adjustment trimmer where I could set the baseline 1TR3 collector voltage. That is the DC voltage at the collector when the Beogram is on and the detector is not picking up any signal from the rotating, empty platter.

For the non-rotating platter scenario the 1TR3 collector is adjusted to about 4 VDC. This is also the voltage the collector should measure if a record is present on the platter.

While set up with the DMM I measured and adjusted the tangential arm position sensor for 5 VDC at the collector of the 4IC1 device (when the sensor lamp is shining through a clear section of the position scale).

Now that those adjustments are made I moved the trimmer for the record detection circuit to the component side of the main board where it belongs. Then I set the Beogram up to measure the 1TR3 collector with my oscilloscope when the record detection circuit is reading an empty, rotating platter.

I measured the expected signal. It is actually a little higher than other Beogram 400x units I have restored. It peaks at around 8 volts and drops down to zero volts as the sensor reacts to the sensor lamp hitting the empty Beogram platter.

Now that the detection circuit adjustment trimmer is moved out of the way and over to the component side of the main board I can take care of the various service manual adjustments.

I used my usual gauge to check and adjust the platter to fixed arm height of 23mm.

Next, I adjusted the tonearm set down limit so the MMC stylus sits about a half a millimeter above the low section of the platter rib.

I also performed the usual check for the tonearm length and parallelism of the arm assembly by checking that the stylus travels a straight line from the edge of the platter to the center.

The tonearm tracking force was calibrated to 1.0 gram and I checked that the 1.2 gram position of the knob also measures 1.2 grams on the scale.

After those adjustments I was finally able to adjust the tracking sensor sensitivity. No photos of that as you really can't capture the setting with a still photo. Details of the adjustment procedure can be seen in this Beolover video.

Next were the calibration of the platter speeds: 33⅓ RPM and 45 RPM.

The final adjustments were for the height of the floating chassis to the Beogram deck so the platter surface was level with the deck.

This Beogram is almost ready for some listening tests. All I have left is to reattach the cabinet trim and the dust cover.