Beogram 4004 (5526): Some Odds and Ends, Final Adjustments and a Test Drive with Dave Brubeck

My restoration of the Beogram 4004 that I was restoring in the last few weeks has come to an end. I procured a near-pristine platter, a nicer looking arm cover, as well as a nearly new looking keypad and installed them. I also added springs to the hood screws that prop them up when the hood is taken off. This makes it much more pleasant to install the hood. They often get lost when people open up the turntable and then forget to put them back in when they built things back together. I sourced them from McMaster. Here are a couple impressions:

this is where the springs belong:

I also fixed the cracked veneer at the back of one of the sides of the plinth:

I used a bit of Alene's Tacky glue and a carpenter's clamp to get things back together:

Almost like new:

Beolovely! 

On to the final adjustments. I adjusted the tracking sensor feedback

and then moved on to the arm lowering limit:

When the arm is down, the needle should miss the lower parts of the platter ribs by a mm or so to avoid calamitous events should the record detection system ever fail (due to a dead photosensor, for example). Then it was time to calibrate the tracking weight:

And then, finally, it was time for a first test drive! I selected a recently acquired Dave Brubeck record "Angel Eyes" on the Columbia label (CL2348). I admit, I partially bought it for the cover during one of my strolls through local vinyl stores...;-). This is an impression of the finished Beogram and the angel eyes:

A very nice album, well suited for casual listening on a Sunday afternoon...The Beogram performed admirably, and it may finally be time to send it back to its owner!

Beogram 4004 (5526): Replacement of Convertible DIN7 Plug with DIN7 Socket and an RCA Adapter Cable

Any restoration of a Beogram should include the replacement of the DIN connector to ensure a low impedance signal path on the way to the amplifier. In the case of a Beogram 4004, the DIN connector is a convertible male DIN 7 plug, where the two additional pins can be unscrewed from small sockets. These two pins would carry the remote control signals from a Beomaster 2400, which is designed to control the 'start' and 'stop' operations of the Beogram 4004. An early form of Beolink, so to speak. But of course, if one does not connect to a 2400, these pins are not needed, hence the convertibility. This shows the plug with the empty two sockets at the ends of the 5 pin half-circle:

This type of plug is no longer available, and so I resorted to replacing it with a DIN 7 female socket, which then connects to a jumper cable with the desired number of pins or RCA termination. In essence this approach converts the Beogram 4004 output scheme to that found in the later Beogram 800x models, who have a DIN 7 socket mounted in the back of their enclosures. That way one can connect with both DIN 5 and DIN 7 jumper cables to a non-B&O or B&O amplifier.

Even cable mount DIN 7 sockets are difficult to find these days, but Steve at soundsheavenly.com can provide them. Here are a couple impressions: This shows the socket soldered on:

and with its shield in place:

And finally with a DIN 5 to RCA adapter cable:

Beogram 4004 (5526): Replacement of Sensor Arm Bulb with a LED Fixture

The final incandescent bulb to be replaced with a LED in the Beogram 4004 (5526) that I am restoring right now was the one in the sensor arm. It is the most difficult one to replace due to the tight space and the requirement that it is positioned perfectly to yield a good sensor signal. I removed the original bulb

and then implanted the LED assembly. This shows the part, which I recently developed in comparison with the original bulb:

The flexPCB based LED fixture folds precisely into the bulb compartment. This shows how I soldered it in:

The red wedge holds the LED in the place where the filament of the bulb was located. This is important that the optics in the arm focus the light into a spot on the platter where the light sensor can 'see' it.

Once the LED assembly was installed, I upgraded the detection circuit with a 2M 25-turn trimmer that allowed me to precisely calibrate the working point of TR3 (which amplifies the sensor signal). TR3 needs to be adjusted that the collector is at 4V DC when no signal (record present) comes from the photosensor. In order to adjust the trimmer with the board powered up, I temporarily installed it on the solder side of the board so I was able to adjust it:

After the adjustment, I removed the trimmer and inserted it from the component side and soldered it in place permanently:

It perfectly fits in the space of R26 that it now replaces. After this was completed, I measured the sensor signal at the collector of TR3 to make sure everything was up to spec:

The Vpp signal should be between 5-6V in order to ensure reliable operation of the record detection mechanism. A test with no record and spinning platter revealed that the the arm would not drop, i.e. the mechanism was working.

Beogram 4004 (5526): Restoration of DC Motor and RPM Stability Test

After restoring the PCBs and implanting LEDs in the RPM trimmer panel it was time to rebuild the DC motor of the Beogram 4004 (5526) that I am restoring right now. 

The first step is to extract the motor:

Then a complete disassembly allows getting to the bearings:

The bearings are the two small donuts up front center. Immersing them into motor oil and pulling a vacuum draws out the air that is in the pores of the oil-depleted Oilite brass bearing material:

Every air bubble that leaves the bearings enables an equal volume of oil to enter and replenish the bearing. After about 12-to-24 hrs the process usually stops and the bubbling ends, indicating that the bearing is full of oil again. Then the motor can be reassembled and a RPM test performed. I usually do this with the BeoloverRPM device that I developed a while ago. It allows logging the RPM every few sec and it transmits the measurement via its serial port to a connected computer where the RPM can be graphed against time. This shows the result of a 24 hrs run of this motor inserted into its Beogram 4004:

This is as stable as these DC motors get. The small fluctuations are a result of the analog control system reacting to temperature fluctuations and other external influences.

Beogram 4004 (5526): Replacing the Incandescent Light Bulbs in the RPM Trimmer Panel with LEDs

Before one can test the RPM stability of the DC motor in a Beogram 4004 (5526) the incandescent light bulbs in the user accessible RPM trimmer panel need to be replaced with LEDs. This lowers the heat load on the trimmers, which in turn increases their stability over time.

This shows the back of the RPM trimmer panel after removing it from the unit:

After removal of the covers the light bulbs can be accessed:

This shows the Beolover LED replacements in comparison with the bulb assemblies:

They are drop-in replacements for the bulbs:

After installation the covers can be replaced and it looks like nothing ever happened:

This is how the LED replacements look in action:

On to the DC motor restoration!

Beogram 4004 (5526): Rebuilding the Electronics

After removing the sub-chassis and rebuilding the transport lock bushings in the Beogram 4004 that I am restoring right now, it was time to focus on the circuit boards and replace the electrolytic capacitors and rebuild the platter motor control circuit. Here are a few impressions:

This shows the main PCB in its original condition:

And after replacing the capacitors with modern 105C rated Japanese made electrolytic capacitors and a new RPM relay and new 25 turn RPM trimmers:

This shows the RPM components:

And a detail picture after installation:

The RPM trimmers need to be installed upside-down that their adjustment screws poke through the circuit board so that one can adjust them while the deck is running.

I also replaced the main reservoir capacitor. This shows the original unit:

And the new one with a 3D printed adapter that it fits into the original mounting clamp:

On to the output board, which on a 4004 also contains a circuit to allow remote control via a Beomaster 2400:

I replaced the output relay and the capacitors, and also installed a switch that allows connecting signal and system grounds if there are humming issues (they often occur when using RCA plug adapters without chassis ground breakout):

That's it for the PCBs. On to the RPM trimmer LEDs.

Beogram 4004 (5526): Installation of New Transport Lock Bushings

When taking out the main PCB for restoration it is a great moment to also repair the transport lock bushings in Beogram 4002/4004 turntables if they need replacing. The 4004 that I am currently restoring had the orange bushing type that usually is degraded at this point in time. This is the typical look when they start to go:

A closer look after removing the top plate of the lock:

It is a great idea to take the sub-chassis out to clean out all of the fragments. They can be lodged under the sub-chassis impeding its free motion during record play, which negates the vibration insulation afforded by the leaf spring mechanism. Luckily, it is fairly easy to take the entire chassis out in the 4004 since it is only connected by wire-to-board connectors. So after removal of the three transport lock top plates it can be lifted out:

A typical 'find' underneath it:

This shows the chassis solo:

Once it is out it is easy to remove the bushing fragments:

and insert the Beolover replacement bushings, which are available via the Beolover Shapeways store (two parts are needed per bushing since they are designed as two parts which insert from below and from the top):

first the bottom part is inserted:

and then completed with the top part:

After doing this for all three locks it was time to put the chassis back in:

This shows one of the bushings after reassembling the locks:

On to the electronics!

Beogram 4004 (5526): Restoration of Arm Lowering and a New Aluminum Pulley for the Carriage

The first step of any Beogram 400x restoration is usually rebuilding of the arm lowering mechanism and getting the carriage to move properly again. The owner of the Beogram 4004 (5526) that I am currently restoring already cleaned and re-lubricated the arm lowering mechanism, but the linkage between the damper and the arm itself was lacking the retaining washer and the small spring that holds the linkage in place. So I needed to remove the sensor arm to repair this issue:

I installed a 3 mm retaining washer and a nylon washer underneath to reduce friction:

After putting the sensor arm assembly back in I adjusted the arm parallelism:

One more thing was needed: A lovely new aluminum pulley provided by Nick (use the contact form or send me an email if you wanted one from him - I'd be happy to get you in touch). These pulleys are a great improvement relative to the often wobbly original plastic pulleys. This shows the original pulley:

and the shiny replacement:

On to repairing the transport lock bushings...