Beogram 4004 Type 5526 - Restoration Project - Mechanical & Electrical Restoration

The previous post for this Beogram 4004 restoration project left off after the initial assessment.

This post shows the mechanical and electrical component restoration up to reassembly of the Beogram 4004 before performing the voltage checks.

With the Beogram 4004 floating chassis out of the cabinet, I removed the solenoid assembly and the arm lowering damper assembly.

For the solenoid, all I did was remove the plunger and demagnetize it.  Over time, the plunger becomes magnetized and begins to "stick" a bit when operating.  Obviously, that is not a good thing so demagnetizing the plunger is a good idea in a Beogram 400x restoration.

As I was concentrating on demagnetizing the solenoid plunger, I forgot to take any photos of the actual demagnetization.  Sorry about that...I will get the photos on the next restoration.

A nice picture of the solenoid though :-)

I did better with the tonearm lowering damper assembly.
Here are the components disassembled.

The restoration task here is to clean the damper components, replace the gasket and apply some new silicone lubricant to the plunger mechanism.

Here I have reinstalled the solenoid, the tonearm lowering damper and replaced the record tracking light source with the Beolover tracking light assembly.

I took apart the tangential drive servo motor for cleaning and checking the condition of the vibration damping material around the motor.  As is typically the case, the damping material was beginning to fall apart.

I replaced it with new damping material, cleaned and polished the servo motor pulley.
I also replaced the tangential drive, plastic pulley with a new, aluminum pulley (from dksoundparts).

Another restoration task I performed on the Beogram 4004 tangential drive components was to clean and lubricate the tangential drive spindle, the front guide rail and the rear guide rail.

I also checked the two position sensor board switches (the end switch and the off switch).

At this point in the restoration, while I have the floating chassis components out of the cabinet,  I like to perform some basic mechanical adjustments like the tonearm bearing height, the tonearm counter weight, the cartridge stylus lowering limit, the arm position and the spindle position.

For the tonearm bearing height, the distance from the top platter surface to the top of the sensor arm has to be 23 mm.  That is the Bang & Olufsen specified height for the perfect vertical tracking angle (VTA) on a B&O MMC phono cartridge.

To perform this adjustment I always remove the spindle assembly so the tangential arm sled can slide back and forth on the two guide rails.  That makes things much easier when iterating through measurements and adjustments on the platter bearing.

Other adjustments I do when the sliding chassis component is in this state are with the tonearm counter weight, tracking force and the cartridge lowering limit adjustment.

There are also the tonearm and sensor arm alignment checks to perform.

The top of the tonearm and sensor arms should be the same and the distance between the two arms should be 7.7 mm.

Here is the floating chassis with its components ready to be re-installed into the Beogram 4004 cabinet.

But first, I spent some time doing the electrical restoration work.

Here is the Beogram 4004 main board, PCB 1.

Before photos -

I replaced all of the electrolytic and tantalum capacitors on PCB 1.  I also replaced the two speed trimmers and speed selection relay.

Transistors IC1 (21 VDC rail power), IC6 (solenoid power) and TR3 (fixed arm sensor signal) were replaced and resistor R26 was replaced with a 5 MOhm trimmer.  

After photos -

Here are the Beogram 4004 Output Board (PCB 8) before restoration photos -

Here are the after photos -

Next was the replacement of the Beogram 4004 power supply reservoir capacitors.
I used the DKAudioLover Main Reservoir Capacitor for Beogram 4002 and 4004 (Types 551x/552x) assembly.

To prepare for voltage testing on the Beogram 4004, I re-installed the floating chassis assembly back into the Beogram 4004 cabinet.

That meant reassembly of the Beogram 4004 floating chassis locks.

Tomorrow I will start in on some voltage checks.  After that I need to install a new sensor arm DKAudioLover light source assembly, two DKAudioLover lamp assemblies for the speed indicators and a nice DKAudioLover SyncDrive platter motor assembly.  With a new sensor arm lamp installed I will be able to adjust the R26 5MOhms trimmer for a proper sensor detector level on the collector of TR3.

Beogram 4002 (5513): Tangential Arm Assembly Oil Cleanup and Restoration

This second Beogram 4002 project from Houston left off with cleaning up debris and oil from the inside of the cabinet. I continued the oil cleanup after removing the tangential arm assembly from the floating chassis.

Oil was found everywhere. From the lowest level of the arm mechanics to inbetween switch contacts.
Here is the tangential arm position sensor assembly completely stripped down for oil cleanup.

Once everything was wiped down and as much of the old oil removed I could begin going through the arm assembly restoration and adjustment steps.

I am doing something a little different on this Beogram regarding the lubrication. Up until now I have always used modern available lubricants like silicone grease and synthetic oils when going through a Beogram 4002 turntable project. I spent the last few weeks searching for the lubricant products that are listed in the Beogram 4002 service manuals. I say manuals because B&O changed a few of the lubricant instructions in the various Beogram 400x manuals.

I will start with the tonearm damper. After taking it apart and cleaning the damper assembly I reassembled it using Dow DC 200 fluid for the damper lubricant.

Next was the tonearm assembly spindle and tie-bar shaft reassembly. For the lubrication of those the service manual calls for the following -
On the spindle: Rocol MTS 1000 diluted to an oily viscosity using Esso NUTO H44 or H32.
On the tie-bar shaft number 137: Molykote DX paste (white)

I was able to find some Rocol MTS 2000 and Mobile NUTO H32 for the spindle lubrication. They were not the easiest products to acquire.

The Molykote DX white paste however is easily available. Here is the tangential arm assembly reinstalled on the floating chassis.

At this point of the mechanical restoration I adjust the tonearm lowering damper, tonearm to fixed arm parallelism and calibrate the tonearm counter weight for the tracking force.

This tangential arm assembly and floating chassis are ready to be reinstalled in the Beogram cabinet.

My next step is to prepare the cabinet by installing new Beolover transport bushings (3D printed parts) and install the Beolover replacement reservoir capacitor assembly (another 3D printed part).

After that it will be time for the remainder of the electrical restoration work - capacitor replacements, relay replacements and the Beolover rebuilt platter motor.

Beogram 4004 Type 5526: Finalizing Mechanical Adjustments

As usual with these Beogram 400x turntables it takes a good number of iterations on the mechanical adjustments before I am satisfied that the turntable is correctly aligned and ready to play records again.

The remaining final adjustments on this Beogram 4004 were the platter height adjustment, tracking force calibration, stylus tracking path check, stylus set down limit and the tangential tracking sensitivity.

For the height adjustment of 23mm between the Beogram platter deck and the top of the fixed arm I ran into a problem where the tangential arm assembly wasn't level enough with the floating chassis frame.

I stripped the Beogram chassis down again and moved the set screws for tangential arm assembly height so they could be adjusted from the top instead of underneath the floating chassis. This will save time in the future and not require taking everything apart again if that adjustment needs to be tweaked.

I ran into a second problem which was with one of the set screws on this Beogram. Someone previously had damaged one of the set screws where it could not be removed. I had to use a Dremel tool to drill it out, then re-tapped the hole for a replacement set screw from my spare Beogram 4004 unit.

Once I was passed that issue it was pretty straight forward to adjust the tangential arm assembly, using the set screws, to get the fixed arm level with the chassis.

I re-installed the floating chassis in the Beogram case and adjusted the platter so the top of the platter is 23mm from the top of the fixed arm. Sorry for no pictures but here is a link to some reference pictures from a previous project.

With the deck height set I went about calibrating the tracking force for the cartridge. The way I like to do that is to set the tracking force wheel to 1 gram, then adjust the counter weight and tracking force wheel as necessary so I measure 1 gram with my digital cartridge scale.

Since I haven't put the Beogram deck completely back together I needed a good base for the scale to rest on in order to measure the tracking force. The ridges on the Beogram 4004 platter don't allow room to put the scale under the tonearm so I borrowed a platter from a Beogram 8002 turntable which is completely flat.

I also left the Beogram 8002 platter in place for the stylus tracking path check.

For the stylus lowering limit adjustment though I switched the platter back to the Beogram 4004 platter as the adjustment is to make sure the stylus lowering limit clears the first ridge of the platter.

That is to protect the stylus if the Beogram ever fails to detect that a record is not present.

Everything is looking good so far. The final adjustment I make is the tangential tracking sensitivity. With the platter belt disconnected from the platter motor I can manually rotate the platter. The adjustment is to set the tonearm down on a record track, then adjust the tracking detector so the tangential arm drive motor begins rotating after a couple of (manual) platter rotations. After that the tangential arm motor should move the arm a little bit on every rotation. Obviously the exact results of this check can vary some depending on the record you use for the test. The Beogram service manual calls for a specific B&O test record (3621001) and track (5) that I have never been able to find. So I typically use a couple of old records I have and test the tracking sensitivity on several tracks.

Once the tracking is set I test play the old record and watch the tangential tracking system do its work.

Next step is to connect this Beogram to my listening room amplifier for the first record play test.