Beogram 4002 (5513): Final Adjustments and Test Drive with Freddie Hubbard's Liquid Love

After installing the Beolover 4002 Commander remote control and internal RIAA pre-amplifier it was time to do the final adjustments on this deck and then give it a first spin. First I adjusted the tracking feedback:

The blue trimmer on my tracking sensor LED light source is very helpful for fine tuning the feedback after doing the coarse mechanical adjustment of the sensor housing relative to the sensor aperture.

The next step was to adjust the subclasses and platter height followed by adjusting the arm lowering limit:

The goal here is to adjust the lowering limit the the needle can go below the record but does not hit the ribs of the platter, should the record detection circuitry ever fail. Then it was time to adjust the tracking weight to 1.2g. I usually replace the flimsy circlip that holds the counter weight screw in place

with a M3 nut and a washer:

This allows fixating the counter weight in place in a way that survives the rigors of shipping. Once that is done the weight adjustment mechanism can be calibrated with a digital balance:

Most B&O cartridges are specified for a 1.2g tracking weight, i.e. it is best to calibrate for that weight.

The final step was to replace the original worn keypad with an almost pristine original pad that I recently was able to acquire:

And then it was finally time to put on a record and give this restored Beogram its first spin of its new life! I selected a recently acquire Freddie Hubbard record from 1975, "Liquid Love". This record is among the less highly rated ones of his output, but it is rapidly becoming one of my favorites. Especially the track "Lost Dreams" is quite lovely. Here is an impression:

I always enjoy playing a Beogram with my 4002 Commander remote installed. In case you wondered how the IR signal makes it from the Apple remote to the Commander receiver board: This shows the IR receiver as it protrudes from beneath the plinth when the deck is fully assembled:

Almost invisible (and fully reversible). Beolovely!

Beogram 4002 (5513): Installation of Beolover Commander MkII Remote and Internal RIAA Pre-Amp Board

The owner of the Beogram 4002 (5513) that I am finishing up asked me to install my 4002 Commander remote control as well as my internal RIAA pre-amplifier module. The Commander allows the full control of the 4002 with an Apple remote, while the RIAA gives the Beogram a high level output that can be directly plugged into any CD/DVD/AUX input on modern amplifiers. 

This shows the RIAA board together with the mounting adapter that elevates it above the headers on the output PCB:

This shows the board installed:

It is soldered into the spot where the output relay is located. The RIAA board design includes a second output relay for the non-amplified signal path, i.e. the RIAA can taken out of the signal path by simply plugging the two plugs into the original headers. See here for more detail about the RIAA board design and use. 

This shows the Commander MkII receiver unit on the bench:

The extension to the right is the IR receiver that feeds through in between the plinth and the enclosure to the outside of the deck. The MkII version has an added auto repeat function which uses a red LED (extension to the left) to indicate the auto-repeat status (LED permanently on: One time repeat, blinking: up to 10 plays and off: no auto repeat). This LED is installed beneath the CD-4 indicator in the RPM adjustment panel. This can be seen here:

The Commander board itself just plugs into the keypad connector, while the keypad plugs into a header on the Commander. One of the four screws that hold the main PCB in place doubles to hold the Commander PCB piggybacking on top of the main PCB.

On to the final adjustments and a test drive!

Beogram 4002 (5513): Replacement of Degraded Transport Lock Bushings and Missing Cabinet Guiding Washers

The Beogram 4002 that I am restoring right now came with the degradation-prone orange transport lock bushings. Furthermore, most of the cabinet guiding washers were lost. A number of Beograms came with plastic washers, which have a tendency to crack and leave the building. This shows one of the locations where the washer was missing:

I installed five new 3D printed washers

This is how they look installed:

It is best to get one printed in black to replace the front-center one. If it is white, it can be seen through the crack between the aluminum panel and the plinth. These replacement washers can be obtained via the Beolover Shapeways Store.

To get to the transport lock bushings one needs to disassemble the locks:

Then the degraded locks can be taken out in pieces. It is a good idea to remove the floating sub-chassis to be able to vacuum out all of the pieces of the degraded locks:

They can impede the floating motion of the sub-chassis if they get lodged beneath it. This photo shows the old bushings and the 3D printed replacements:

Each replacement bushing comes in two parts. One is inserted from the bottom and the other from the top:

These parts are also available via the Beolover Shapeways Store. Once the bushings are installed the chassis can be reinstalled. This shows one of the bushings in place in a reassembled lock:

Almost done with this Beogram...on to replacing the corroded DIN5 plug.

Beogram 4002 (5513): Restoration of a Cracked Hood - Another Process Improvement

The Beogram 4002 that is on my bench right now came with a hood that was cracked around the holes where the hood hinge is attached. In this particular case the left side was completely broken out

and the right side had a crack all the way through around one of the attachment holes:

As usual, the first step was to 'save what could be saved', i.e. I glued the cracked parts back on using Weld-On #4 acrylic solvent. This solvent is extremely low viscosity and can be directly injected into a crack where it gets sucked in due to capillary forces. This shows the broken parts fused back together:

If done right, this step already creates a pretty strong bond between the broken parts. The solvent dissolves the plastic at the crack and after the solvent has evaporated the plastic is (in theory, at least) again a homogeneous part. But of course, nothing is as strong as the original cast material after is gets broken into pieces.

Therefore, the best way to finish this repair is to fuse thin patches onto the cracked areas. Unfortunately, these patches need to be very thin. On the inside due to the tight fit of the metal hinge part, and on the outside for cosmetic reasons since the patch needs to 'hide' underneath the aluminum strip that is glued onto the outside areas to hide the screws.

This time I made the patches manually myself from a 20 mil PETG sheet using 3D printed templates, scissors and a hole punch. PETG was necessary, since apparently there are no thin acrylic sheets available. PETG bonds well with acrylic since it is solvent compatible. This shows the hole punch in action on a cutout patch:

In the past I was not satisfied with my hood repair protocol since it was always difficult to clamp the patches properly to the hood all over their contact area. So this time I improved my method by using 3D printed clamping parts that could be directly squeezed together via bolts through the hinge holes. this shows all the used parts for this repair:

The metal parts are necessary to prevent the 3D printed PLA parts to bond with the plexiglass while the glue is squeezed out at the fringes. This shows the parts in action on the left side:

you can see some dissolved plexiglass and Weld-On #16 (higher viscosity since the glued back together hinges are a bit rough, so #4 does not work that well) being squeezed out on the sides. This is great since it essentially 'sinks' the patch a bit into the hinge bulk. This results in a lesser thickness increase, making the repair less intrusive for the optics of the outside of the hood. This shows the process for the right side:

After doing this for both the inside and outside patches (it is difficult to do both at the same time since the solvent bonds quickly) the squeezed out acrylic/PETG can be trimmed with a razor blade:

After letting it cure for 48 hours I bolted the hinge back in:

Once the bolts are in, the aluminum trim needs to be glued back on. I usually use industrial strength 3M 300LSE laminating tape. This is essentially a glue layer on a piece of wax paper. Difficult to handle, but it does not add any significant thickness to the laminated stack. After trimming the tape with a razor blade along the aluminum trim, I took the paper off and pressed the aluminum trim on. Then I fixated everything in place for a day with locking pliers:

I protected the aluminum trim with a thick piece of cardboard. The red part is one of my templates to mark up the PETG sheet for cutting out the outer patches. It distributes the force of the pliers. 

This shows the hinge areas after removing the clamps:

The patches are almost invisible! The 3D printed blocks really helped flattening the patched areas.

Now it was time to finish the hood up with a polishing workout. It had the usual scratches on the top surface:

This warranted an initial sanding step with 320 grit paper to equalize the surface. Then I polished it back in several steps with ever finer grit paper. This shows the surface after the 400 grit wet polishing step:

This is how it looked after the final step:

Pretty shiny, but of course not perfect. Polishing can only do so much, and small imperfections can be seen under certain lighting conditions. But for the usual presentation of the Beogram on a sideboard or similar, this looks pretty newish! So far so good! The final act on this hood was to install new rubber bumpers to ensure that the hood is level when closed. Rubber bumpers also ensure a good sound signature when the hood meets the plinth. This shows a degraded bumper:

I drilled them out with a 2 mm bit:

Then I superglued sections of a 2 mm O-ring into the cavities:

After the glue had hardened, I cut them to length using a 3D printed template:

They need to be about 1 mm in length that the hood is horizontal when closed:

And that was it! This hood is back in business!

Beogram 4002 (5513): Replacement of Sensor Arm Bulb with an LED Assembly

After rebuilding the DC motor of the Beogram 4002 that I am restoring right now it was time to replace the light bulb in the sensor arm. This bulb is critical for the record detection circuit, and replacing it with an LED makes sense since LEDs last much longer than light bulbs. This shows the bulb compartment extracted from the arm together with the flexPCB based LED assembly:

The LED assembly 'mimics' the light bulb in terms of drawn current to be compatible with the light bulb detection circuit. This circuit monitors the current through the bulb, and disables the record detection circuit in case the bulb dies. LEDs draw much less current than the bulbs, and therefore an additional current path needs to be provided on the LED board in parallel to the LED itself.

The LED board folds into the compartment:

After soldering it in, I started the Beogram to see if everything works:

The warm-white LED has enough red emission to render the B&O logo properly red as if it were illuminated by the original incandescent bulb.

The final step of any light source replacement in the sensor arm is to check if the ribs on the platter are properly detected. TR3 amplifies the sensor signal and its collector needs to be at 4V DC when there is no signal (record present). Unfortunately, the circuit design of the 4002 biases the base of TR3 via a single resistor connected to the collector. This makes the working point of TR3 dependent on its current amplification factor, which can vary widely between transistors of the same type. Hence, many Beograms have a too small voltage at the collector of TR3, reducing the signal generated by the ribs on the platter as they go by underneath the sensor. This can be rectified by replacing R26 (1 MOhm) with a 2 MOhm multi-turn trimmer:

I usually install the trimmer first on the solder side to be able to adjust the collector voltage  with the board installed and the turntable on. Once the 4V are set, the trimmer can be installed from the component side:

The final step is to measure the sensor signal at the collector with the platter spinning underneath:

This Beogram passed the test with flying colors: The signal is very close to the prescribed 6Vpp. If the signal is too small, then TR3 is not biased correctly, and if the signal does not go to zero when a rib goes by, then the LED or the bulb is not in the correct location within the bulb compartment of the sensor arm.