Michigan Beogram 8002 Floating Chassis Components Restoration

I began the restoration of this Beogram 8002 turntable with the floating chassis components.

The main reason for that is two broken parts I discovered during the initial assessment.
I wanted to tackle those two (key) problems first because I wanted to make sure they could be properly fixed.

For the spindle nut with a broken guide wall for the bracket that connects it to the tangential arm assembly...I decided to go with a spare (or donor) spindle nut from my box of Beogram 800x turntable parts.

In the case of the broken tab that secures the Beogram 8002 position sensor assembly...I had to design a 3D printed part that would properly secure the broken tab and still allow the tab to let the sensor assembly board be removed.

It took some modification of my initial design but I finally achieved what I was after.
The 3D part glues onto the molded plastic that comes with the Beogram floating chassis.

The broken, plastic tab is also glued to the 3D part and the area of the chassis it broke off from.

The ends of the 3D part wrap around the chassis base on all four sides to provide strength.
The end closest to the servo motor has to have a slot for the sensor assembly.
The 3D part wall on the spindle side had to be made smaller than I originally designed it to leave room for the sensor wheel and to attach/remove a rubber belt.

Here is another view.

While I had the floating chassis components where they are still easily accessible, I decided to perform a few Beogram 8002 adjustments that involve the tangential arm assembly.

To do this I removed the spindle assembly and just left the arm assembly on the two rails.

This allowed me to manually slide the tangential arm assembly wherever I wanted to without manually rotating the spindle (which gets old fast).  I also didn't want to wait until the electronics were completed and working...then take the arm assembly out again.

With this setup I adjusted the height of the fixed-arm (sensor arm) relative to the top of the platter.
The distance per the service manual is 19.5 mm (different than the Beogram 8000 and Beogram 400x turntables).

That adjustment screw is shown in blue text in the above photo.

With the fixed-arm height set per the service manual the next adjustment is to make the top of the tonearm match the top of the fixed-arm.

The adjustment screw for the tonearm height is underneath the tangential arm assembly so you can see why I want to get it out of the way first and not come back to it.

I am not showing the phono cartridge tracking force calibration here but I did do an initial calibration of the tracking force counter-weight, phono cartridge and force selection slider while I had the floating chassis components apart.  I will do a final check later when the Beogram is assembled for testing.

Next, I cleaned and applied rubber cleaner/treatment to the two damping rubber inserts on the rear tangential arm rail. 

Note that the rubber dampers are only on the rear rails of Beogram 8002 turntables used with 60 Hz line voltages.  They aren't necessary where the line voltage is 50 Hz.

The last floating chassis component tasks I worked was to replace the audio muting relay and the two capacitors on the +5 VDC regulator.

Here is the muting relay replacement.
Note that the Beogram 8000 has a different muting relay.

Here are the only two floating chassis mounted electrolytic capacitors that get replaced.

The next post for this Beogram 8002 project will focus on the main electronics restoration work.

Beogram 4004 (5526): Full Functional Restoration (Exciting: Melted Platter Motor Spark Snubbers!)

This post discusses the functional restoration of a Beogram 4004 that I received from a customer in New York a while ago. My initial assessment of this unit is posted here. 

This shows the Beogram in 'service position' with the aluminum covers and platter removed:

As usual, I started with the DC platter motor since it takes a few days to get the bearings re-infused with oil. In this particular case the motor was also interesting since I never had a completely seized motor on the bench before. This shows the motor after removal:

I opened it up and found that the spark snubbers that are soldered to the rotor between the three coils had completely melted, and that essentially cemented the rotor to the magnetic stator mounted on the inside of the enclosure:

I was finally able to scrape enough of the melted casings off to be able to liberate the rotor from the enclosure:

Completely blackened spark snubbers:

They must have all short circuited together. Pretty rare, I would say. Usually, one of them dies and that causes the motor to run very unevenly. I examined the brushes:

They were quite blackened, indicative of high currents flowing. I removed the spark snubber fragments:

Then I proceeded to get the bearings out for oil-infusion. They are the two small donuts on the black rubber pad:

I immersed them in synthetic oil and pulled a vacuum. Immediately strong bubbling started:

After a few minutes it got so strong that the oil foamed up and made a mess in the vacuum chamber:

Definitely a remarkable motor. I am saying this after having restored probably about 150 of them by now...;-).

While the oil infusion was carrying on, I focused on the rest of the restoration work. The next step was to restore the mechanical systems on the carriage. This shows the setup in original condition:

I removed all the moving parts of the arm lowering mechanism and the carriage translation system:

This shows the removed components ready for the ultrasonic barth:

I also removed the solenoid since they often have magnetized plungers:

I took the plunger out and tested its magnetism with a M3 steel set screw. Indeed, the plunger attracted it signaling that it needed de-magnetization:

I treated it with my tape head de-magnetizer and it stopped attracting the screw:

All good in the solenoid department again! Magnetized plungers usually lead to delayed arm raising, which can result in the needle dragging across the record during the automatic carriage return at the end of playing a record. With a $800 rebuilt cartridge on the arm this can be a bit disturbing!...;-).

There is one more moving part that often gets stuck due to hardened lubricants, which is the damper-to-arm-linkage. It is tucked in-between the tone and sensor arm assemblies. Its pivot point is on the sensor arm assembly. One can see the end of the linkage stick out from the v-cut in the small metal piece that is bolted to the counter weight:

I removed the sensor arm assembly and extracted the linkage:

Of course the small copper plate that is double-sided-taped to the assembly came loose after poking it a bit with my tweezers. After re-installing the linkage, I cleaned the degraded tape off the little plate and epoxied it back into place:

Another item to be done on the carriage assembly is to replace the incandescent bulb in the tracking sensor with a Beolover LED replacement. This shows the original setup:

Removal of the bulb housing reveals the tracking aperture:

This shows the original bulb setup (left) next to the Beolover Tracking Sensor LED Light Source (Beogram 4002 and 4004):

In the meantime the ultrasonic cleaner had done a nice job on the extracted parts and they were clean and shiny again:

As usual I put in a new damper gasket before re-assembly:

Then I put everything back into place:

Before I installed the new pulley I realized that the carriage motor sat completely loose in its enclosure:

This usually indicates that the foam damper piece inside the enclosure has degraded completely. I extracted the motor assembly:

Indeed the foam had turned into a powdery mess:

I cleaned the mess up

and installed two EPDM rubber rings as vibration dampers:

Then I put the motor back into place

and installed a new precision machined Beolover Aluminum Carriage Pulley for Beogram 4002 and 4004:

This concluded my work on the carriage. On to restoring the circuit boards. It is good practice replacing the two Darlington power transistors mounted on the solder side of the main PCB first, while it is still installed. This shows 1IC1, originally usually a TIP120 type:

1IC1 regulates the 21V power rail of the turntable. I usually replace it with a higher current rated TIP102 hoping it will last longer. I also add a 100nF capacitor between emitter and ground (yellow) to quench a high-frequent oscillation that frequently occurs when using modern TIP devices in this circuit:

After replacing 1IC4 with a TIP107 it was time to remove the board to access its component side. This shows it in its original condition:

This shows the 'RPM section' in more detail:

I replaced all electrolytic capacitors, power transistors, RPM relay and trimmers, as well as the sensor arm transistor 1TR3, which is often out of spec imperiling proper funcitoning of the record detection circuitry. This shows the restored board along with the replaced components:

A detail shot of the rebuilt RPM section with new 25 turn encapsulated RPM trimmers and a new Beolover National Relay Replacement for Beogram 4002 and 4004:

Beolovely! On to the output PCB, which in the case of a Beogram 4004 not only contains the muting relay for the output channels, but also the remote control circuitry that allows control of the turntable via the remote of a Beomaster 2400. This shows the board in its original condition:

A detail shot of the muting relay circuitry:

Visual inspection yielded a shorted and burnt out 8C14 capacitor, which probably explains some of the operational issues I saw during my intial testing of the unit:

This type of failure is a frequently encountered issue with Ta electrolytic capacitors. They tend to short out in a fiery manner. I replaced all the electrolytic capacitors and the output relay:

Here a detail shot of the rebuilt muting section:

The red component in front of the output jack is a switch that I implemented allowing connecting system and signal grounds. Usually connecting the two is a reliable remedy for quenching hum issues when connecting the Beogram to non-B&O equipment.

There were still three light bulbs left to be replaced. Two of them were in the RPM panel above the keypad to back-illuminate the user accessible RPM trimmers. This shows the panel removed and turned upside-down:

The bulbs are behind two covers that can easily be removed with a screwdriver:

I removed the bulbs and replaced them with a set of Beolover RPM Panel LED Backlights for Beogram 4002 and 4004 (Types 551x/552x):

They solder directly to the solder points of the light bulb and essentially function as extensions of the original circuit board:

The LED assemblies do not interfere with the bulb covers, which can be replaced for an original look:

The last bulb is in the small compartment at the end of the sensor arm. This shows it pulled out with the bulb still installed and the Beolover Sensor Arm LED Light Source (Beogram 4002, 4004 and 4000) with alignment aid next to it:

I removed the bulb abd implanted the LED assembly:

Then I removed the original reservoir capacitor

and the floating chassis. At that point the enclosure was finally empty:

I vacuumed all the debris from the degraded transport lock bushings out:

This shows the cleaned out enclosure:

Then I started replacing all the components. First, I put in a new Main Reservoir Capacitor for Beogram 4002 and 4004 (Types 551x/552x). Beogram 4004 are usually fitted with a single capacitance reservoir capacitor, i.e. all that I needed to do was soldering the black and white leads to the correspondingly labeled PCB terminals:

At this point I also checked the fuses in the fuse box. I found two 1.5 Amp fuses which are much to strong for this design:

I replaced them with proper slow (T) 250mA fuses as specified on the fuse cabinet lid:

Then I set out to install the floating chassis. Before doing so I needed to install new transport lock bushings. This shows one of the empty orifices that had lost its bushing:

This shows a set of new Transport Lock Bushing Set for Beogram 4000, 4002, and 4004:

They are easily installed since they come in two halves, one of which is inserted from the bottom and the other from the top:

After installing all three bushings it was time to put the floating chassis back into its place:

After installing the PCBs and the keypad it was time for adjusting the bias of the sensor arm transistor to get 4V DC at its collector:

After the adjustment I moved the trimmer over to the component side:

Then I tested the control system of the Beogram. After pressing start the carriage completely ignored the LP setdown point and proceeded towards the center of the platter. This suggested a problem with the carriage position sensor. It is situated on the PCB underneath the plexiglass 'ruler' that is bolted to the carriage assembly. After removal of the ruler assembly the board can be inspected:

Instead of spending time diagnosing the system I decided simply installing a Beolover Carriage Position PCB for Beogram 4002 and 4004 (Types 551x/552x). It is a direct plug-in replacement for the original board:

This shows the board installed:

It features a modern monolithic IR interrupter as well as new SO and ES switches. The board also features an integrated diagnostic feature where a LED can be activated with a switch for signaling successful sensing events. With the new board in place the LP setdown point was properly detected, so all good now in the carriage position sensing department!

Then it was time for doing the mechanical adjustments to get the platter parallel to the arms and at the correct height. Then I adjusted the leaf springs to get the platter flush with the surrounding aluminum panels. Only when this is properly done the tracking weight, arm lowering limit and tracking feedback can be adjusted.

First I replaced the flimsy circlip that holds the counterweight adjustment screw in place

with a M3 square nut and a washer:

This allows locking the tracking weight calibration in place so it survives transportation. I adjusted the weight to get the proper 1.2g at a weight dial setting of 1.2:

The dial is notoriously imprecise across its range, therefore it is best to adjust the weight in a way that the dial is accurate in the range of the typical tracking weight recommended for B&O cartridges. After setting the tracking weight I did the tracking feedback adjustment: 

The next step was reassembling the platter motor and installing it for testing. The bubbling from the bearings had stopped at this point and so I extracted them from the oil:

I installed new non-polar TVS devices in lieu of the burnt spark snubbers. This shows them prepared for installation on the black pad:

I soldered them between the three solder poles of the rotor:

If you try this at home, make sure the TVS packages are mounted below the commutator.

Then I put the motor back together and installed it in the Beogram. The next step was the performance of a 24 hrs RPM stability test with the BeoloverRPM device:

In its 'slow' mode the BeoloverRPM allows logging the RPM in 10s intervals, which is a great way to confirm any RPM inconsistencies that would otherwise be difficult to detect by just listening to records. This is the curve I measured after about 24 hrs:

This is pretty much as good as it gets with DC platter motors. 

Next, I ran the BeoloverRPM in its 'fast' mode to get a reading on 'wow and flutter', i.e. RPM changes on a short time scale. This shows the BeoloverRPM in action in fast mode:

In the fast mode a RPM measurement is recorded each time a platter rib passes under the sensor. This generates high-resolution RPM data that looks like this:

This graph covers about 40 platter rotations, or about 80 sec. of runtime. The interesting pattern is a convolution of real RPM changes and a measurement artifact that is a result of the very slightly irregular spacing of the platter ribs around the platter. On closer inspection, the zig-zag pattern is repeated every 24 measurement points (there are 24 ribs...) and can be regarded as a 'fingerprint' of a particular platter. It turns out that each Beogram platter has a distinct pattern due to manufacturing tolerances when the slots were machined for the black rubber ribs.

The overlaid wavy pattern, however, reflects real RPM changes that are introduced by the feedback based control system that keeps the motor RPM constant. An evaluation of this wave pattern yields a wow and flutter percentage of about 0.1%. The service manual lists 0.05% as the spec for the DC platter motors, but this 2x difference may well be related to the different way this was measured in the 1970s in absence of modern microcontrollers. So we can conclude this motor is ready for duty again! Pretty amazing considering its bad condition when I opened it up!

My customer wanted a Beolover Commander Remote Control for Beogram 4002 and 4004 installed to protect the keypad from further deterioration. The Commander enables full control of the Beogram with an Apple remote. It also adds auto-repeat functionality. The installation is easy, no soldering required. The Commander plugs directly into the keypad jack. This shows the keypad still plugged in normally:

I removed the RPM panel, which revealed broken out plexiglass fixtures that hold it in place with spring clips. Left side

and right side:

Luckily, these days there are reproduction parts available from the dksoundparts store in Denmark. This shows the new parts on the left and the old parts on the right with the spring clips already removed in the center:

I installed the spring clips in the new plastic parts

and then bolted the parts into the keypad assembly. This shows the parts installed on the left

and the right side of the keypad:

Then it was time to install the Commander. Since this Beogram is a 4004 model, the Keypad gets its power from the output PCB via the harness below the keypad:

The Commander board needs to get power via this connection, too, and therefore the 4004 breakout board needs to be installed:

The white wire harness originating from the breakout plugs into the Commander board, which is installed on the keypad jack on the main PCB:

Then I cleaned the aluminum panels and platter and finally it was time to give this fully restored Beogram 4004 a first test spin. I selected one of my favorite records, "Feel" by George Duke. He recorded this album for MPS records in 1974 (MC 25355). A perfect match for this lovely Beogram! Of course this album was cleaned ultrasonically using a CleanerVinyl ProXL setup.

Beolovely! I will now play this Beogram a bit more to make sure there are no intermittent issues and then it will be time to send it back to is owner!