Beogram 4000: Glueing a Delaminated Platter Back Together and Installation of New Cabined Guidance Washers

The Beogram 4000 that I am restoring right now unfortunately had suffered some transport damage due to the inept packaging job of the ebay seller. Since he did not take out the platter, it bounced around and in the process delaminated into two parts. This shows the bottom and top parts of the platter:

It is interesting to have a peek inside the platter assembly. It appears that the lower part of each platter, which provides the main weight of the assembly, was individually balanced, similar to what is done with car wheels after putting on tires. They did that by drilling out small portions of the materials on the too heavy side of the platter (you can see the red pen mark from the balancing process next to the drill pattern):

It is also clear from the markings on each of the ribs of the lower platter that both parts were glued together. Inspired by this finding I used a slow curing epoxy glue, which I applied next to the original glue spots:

Then I placed the top part off the platter and aligned it as good as I could. A 4002 platter served as weight to secure both halves in place while the epoxy cursed for 24 hrs:

In the meantime, I replaced the old cracked cabinet guidance washers with new 3D printed ones. This shows the original center washer at the front of the enclosure:

This one is a strange design aspect of the 4000...it seems to be a flat Teflon washer that has no guiding feature. This one is best replaced with a 3D guidance washer printed in black, since white ones are visible from the front through the crack between the cabinet and the aluminum panels:

This shows the complete set of five 3D printed guidance washers:

They are available through the Beolover Shapeways store (see link under 'pages' on the right).

Beogram 4002: DC Motor Restoration and Dependence of RPM Performance on the Value of C10

I recently received two DC motors for restoration that were extracted from Beogram 4002 units that Sonavor is currently rebuilding. This shows one of the motors:

The first step for motor rejuvenation is performing an oil infusion of the brass sleeve bearings which are usually running try after 35+ years of operation. This requires a complete disassembly of the motor:

The bearings are on the black pad in the front. Their oil infusion requires placing them under vacuum while immersed in oil:

The air bubbles emerging from the pores of the bearings signal that the infusion process is progressing. As the vacuum draws the air out, oil replaces the air in the pores and the bearings regain their ability to form an oil film around the motor shaft. After 24-48 hours this bubbling typically stops and the bearings can be extracted for reinsertion into the motor. This shows the bearings in place:

Once the motor is back together it is time to give it a 24 hrs stability test with the BeoloverRPM device which allows the logging of the RPM over extended periods of time. This shows it in action:

The BeoloverRPM is available to other enthusiasts. Just send an email or use the contact form on the right if you are interested.

For a while now I am trying to figure out how to get these DC motors running with the highest stability. Since their control system is fully analog, factors like friction and temperature can significantly alter the stability of the system. Especially capacitor C10 which governs the feedback response of the system has a strong influence on the RPM stability. Over time B&O changed the C10 value between three values: 0.33uF, 0.47uF and 10uF. Our research has shown that most motors have a 'preferred' value for best performance. Which one can only be determined at this point by testing them with different values and then selecting the best. I did this for these two motors. This are the graphs that were measured:

The top two graphs show the RPM performance of both motors with 0.47uF installed for C10. Especially the red curve (motor #1) has some pretty big spikes to higher RPM, indicating that the feedback tends to over compensate the system and under certain conditions the RPM spikes. The same motor run with 10uF in place showed a perfect curve as shown below (light red). Motor #2 also benefitted from 10uF, but not very significantly. It already performed fairly well with the 0.47 uF value soldered in.

At this point it is a mystery why some motors react different from others. They show the same coil resistance and draw the same current etc...i.e. they are virtually identical in all measurable values. My speculation is that these performance variations may have to do with mechanical friction in the motors, which by itself is a damping factor that acts on the control system's transfer function. Until we understand this a bit better, I guess the best approach is to simply determine the best value empirically and enjoy some nice vinyl records!

Beogram 4000: Upgrade of Signal Path with New DIN5 Plug and a Grounding Switch

As usual the original DIN5 plug on the Beogram 4000 that I am currently restoring was badly oxidized. This shows the original plug:

I replaced it with a new all-metal plug that has gold coated terminals:

Another useful upgrade of the signal output of any Beogram is the installation of a switch that allows connecting signal and system grounds. This is a useful feature if the Beogram is ever to be used with a DIN5 to RCA adapter. Since RCA cables do not carry the system ground, connecting it to the signal ground on the Beogram often eliminates humming. This shows the output terminal assembly of the Beogram 4000 in its original condition:

This open layout makes it very convenient to add a switch:

The shown switch position connects the two ground. Flipping the switch would open the connection.

Beogram 4000: Replacement of Sensor Arm Light Bulb with an LED

The final incandescent bulb to be upgraded with an LED in the Beogram 4000 that I am restoring right now was the one in the sensor arm. This LED is the most difficult to replace due to the compact dimensions of the compartment in which it is located. This required the design of a flex PCB based solution since this LED not only needs a current limiting resistor, but also a current bypass to simulate the presence of a light bulb drawing a much more significant current than a modern LED. This current is used by the control system to detect if the light bulb is working, i.e. the LED setup needs to draw a similar current. This shows the bulb compartment pulled out of the sensor arm:

I removed the bulb. This shows the bulb together with the already folded LED assembly:

Then I installed the flex PCB into the bulb compartment. This shows it powered up:

The warm-white LED emits enough red photons to properly light up the B&O logo like the original bulb.

Whenever the sensor arm light source is replaced the record detection circuit needs to be tested to make sure the absence of a record is properly detected. This shows the signal measured at the collector of TR14, which amplifies the sensor response for the control system:

It is as specified in the manual, having an amplitude of about 2V spanning from 0.2 to 2.2V. All good in the sensor department!

Beomaster 8000: From One Beomaster 8000 Project To Another

Having just shipped back the most recent Beomaster 8000 and Beogram 8000 restorations to their owner I find myself continuing on with another Beomaster 8000 restoration project. Maybe 2018 will be the year of the Beomaster 8000. At least on the sonavor workbench :-).

As a Beosystem 8000 owner myself I understand these fellow owners wanting to have a fully working system again.

This works out good for me because my workbench is already in the Beomaster 8000 mode. I have the parts ready, the work bench ready and the test bench ready so it is time to begin.

First though, this Beomaster 8000 arrived in the best shipping box I have ever seen. It is not a Bang & Olufsen original box. It is better. I haven't ever seen a kübox shipping box before this one. It is very well designed and for the Beomaster 8000 well worth the cost I think. The Beomaster is a really heavy receiver. It benefits from a really sturdy shipping box to ensure safe transit. 

Another cool packing product the owner used on this shipment was Sealed Air Instapak cushioning. These are various size bags with foam cushioning that is activated during the packing process so the expanding foam molds itself to the item being protected. The shipping box limits the foam bag expansion so the bag forms itself to the space between the Beomaster and the shipping box.

Inside the shipping box was another nice Beomaster 8000. 

The cosmetic condition of this unit is pretty good. I don't see anything broken so far. There are some surface scratches though and as usual the flat, metal spring clips for the center bar are not a complete set.

This Beomaster was manufactured around the same time as the previous Beomaster 8000 project. Like that one this Beomaster has the later, improved microcomputer box that is easy to open up.

The restoration on this Beomaster will also be pretty much the same scope as the previous Beomaster 8000 project.  Electrolytic capacitors will be replaced with new high quality capacitors that are rated up to 105°C. Most capacitors 4.7uF and lower will be replaced with WIMA MKS polyester capacitors. The old LF353N audio OpAmps will be checked and likely replaced with new ones. The old, dry heat sink compound will be cleaned off and and replaced with SIL-Pads. The Beomaster display panel will be reworked with new light sources installed. The volume and tuning wheel sensors will be checked and probably replaced with new emitter and detector devices as I have been running into a number of these with failing sensors.

Enough talking about the project. It is time to get started.

Beomaster 8000: Wrapping Up Loose Ends & Buttoning Back Up

Over the weekend I finished up a few loose ends on the Beomaster 8000 project and finished the reassembly of this fine receiver.

Because earlier in the project I had found a fault in the rotary encoder sensor assembly for the volume dial I didn't feel comfortable leaving the rotary encoder sensor assembly for the tuner dial in its original state. If the sensor went out in the volume control then the same parts in tuner dial might be due. It is an easy replacement so it is better to do that than risk the sensor failing later.

Loose wiring and bad connectors are one of the biggest problems on the Beomaster 8000. Another common issue is the two ribbon cables that connect to the control keypad board start to come loose over time. That can result in strange behavior. These cables are still working good so I will just add some black hot glue where they are coming loose.

But first the tuner dial rotary encoder sensor update.

I replaced both sensors and the emitter then put the sensor assembly back in place with the re-glued ribbon cables. I also added a dab of hot glue where the small volume and tuner sensor boards attach to the dial. That insures they won't work out of position during shipping.

Earlier in this Beomaster restoration I had to make a mechanical fix of the tone control & filter panel because it had a crack in it. During this reassembly I discovered that one of the mounting screw tabs of that panel was also cracked. Another fix requiring some epoxy.

I had to let the epoxy cure for a few hours but eventually I was able to return to the Beomaster reassembly tasks.

The reattachment of the tone control & filter panel door takes some careful maneuvering to get back in place.

The hard part is done. Next is to add the display cover and heat sink cover.

Then a couple more trim pieces and this Beomaster is finally all back together. It is now ready for some final play testing.

What a nice receiver. I couldn't wait to try it out with its Beogram 8000 I restored earlier so I cleared some space on my largest workbench. A little messy but I was also able to fit in a Beocord 9000 and connect the Beomaster to a pair of S70 speakers. I also have a remote control for the system and it works beautifully.

I will continue this integration test for a couple of days and start preparing the shipping boxes for this Beogram and Beomaster to return to their owner.

Beogram 4000: Restoring the Carriage Position and Solenoid Driven Switches

After rebuilding the keypad cluster of this Beogram 4000 it was time to see to the remaining mechanical switches that control the Beogram's performance. There are two clusters, one beneath the carriage where the switches determine the position of the tonearm, and the other next to the solenoid. The solenoid activated switches are responsible for the activating the tracking mechanism, opening the outputs when the needle is in the groove and to regulate the solenoid power down once the arm is lowered.

This shows the carriage position switches. For getting to them it is best to drive the carriage inwards and remove the red position indicator assembly. Then the board is fully accessible:

After unsoldering the two leads that power the carriage motor and removal of two screws the board can be pulled up and turned around:

Some oxidation is visible on the back of the terminal tabs. For some reason the carriage position switch terminals are usually less oxidized than the other switches under the keypad and next to the solenoid. I removed the terminals

and coated them with gold:

Then it was time to solder them back in and clean the plastic plungers that activate the switches from 40 year old hardened grease. Then I turned my attention to the switches next to the solenoid. The single switch assembly that controls the solenoid power can be directly accessed after removing the two screws that hold it in place:

I extracted the terminal and then removed the assembly that holds the output and tracking activation switches:

This assembly needs to be taken apart while not ripping the thin wires off that are connecting the switches to the control system:

Once this was done I extracted the three terminals. This shows all four terminals as extracted:

'Beautifully' oxidized, I'd say! I brushed the oxide off with 2000 grit paper and a fiber glass brush and then coated them with gold:

That looked much better! I put everything back together and gave the system a first test...Good news: so far everything seems to work...the carriage is now setting down the arm at the 12 inch point and the solenoid actuated properly. A significant milestone has been reached in this restoration!