Beogram 4002 DC Motor Restoration

I recently received two Beogram 4002 DC platter motors from Michigan for restoration. In the following I will show the process for one of them. The other received the exact same treatment. This shows motor #1 as received:

I disassembled the motor to extract the bearings for oil infusion under vacuum:

The bearings are the two small donuts up front on the black pad. I immersed them in motor oil and pulled a vacuum:

Immediately bubbling started indicating that air was drawn out from the porous bearing material to make room for oil inter diffusion. After about 72 hrs the process stopped and I removed the bearings from the oil:

Then I reassembled the motor and installed it into one of my Beogram 4002s for testing with the BeoloverRPM device:

the BeoloverRPM device allows logging the RPM over extended periods of time. Perfect for detecting elusive intermittent RPM changes. This graph shows the two curves I measured for motors #1 and #2:

These curves are as good as it gets with the Beogram 4002 DC motors. Motor #2 (blue) is slightly more 'unruly' than #1. In my experience some motors can take a while to settle after restoring them, and I think after playing a stack of records, it may well get as stable as #1. At any rate the fluctuations are well below what humans can detect, i.e. these motors are both ready again for business.

Beogram 4002 Type 5513: Return to the workbench for a new phono cartridge mount

With the third Beogram 4002 Type 5513 delivered to Houston the number two Beogram came back to my workshop. It is suffering from a broken phono cartridge connector on the tonearm.

This type of problem is common on the Beogram 4000 turntables (as they are the oldest in the series) but is not unheard of in the Beogram 4002 Type 5513.  I ran into a faulty phono cartridge connector on a Beogram 4002 Type 5513 back in 2017.

This problem would be a huge problem for an owner and require stealing a good connector off another Beogram turntable if it weren't for Beolover having a replacement part for it.

I will use the Beolover replacement part to repair this Beogram 4002 turntable.

First off I need to prepare the Beogram for the new phono connector.

That means removing the tonearm by unscrewing the two mounting screws that attach it to the tonearm base assembly.

The aluminum tonearm tube pulls out to expose the phono wires and a small transfer board. The transfer board is where the color coded wires from the phono connector connect to the very thin wires that take the signal through the tonearm base.

I am using a small mirror in the two photos below to show the top and bottom sides of the wiring transfer board.

After desoldering the phono wires from the board the tonearm assembly can be removed.

I performed the usual boiling water to ice water trick to loosen the glue that holds the tonearm cartridge connector inside the aluminum tube.  That let me push the connector out of the tube so it can be repaired.

Unfortunately I don't have the Beolover replacement phono connector in my stock of Beogram parts so I quickly ordered one.

In the meantime....continuing the repair preparation, I turned the tangential arm assembly over so I can easily get to the wiring board.  When the replacement phono cartridge connector arrives I will install new phono wires from the new connector to the transfer board.

It shouldn't take long to reattach the wires and this Beogram will be ready to go again.

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!

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!