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.