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 4004 Type 5526 - California Project - Floating Chassis and Circuit Board Restoration

The previous post for this Beogram 4004 restoration finished up the initial disassembly and cleaning of Beogram.

In this post I finished up the mechanical restoration tasks and the restoration of the circuit boards to the point I was able to test some basic functions of the Beogram 4004.

Power circuitry, tangential arm control and the platter motor are now working.

Here is a photo of the initial start play test.

To get to this point I had to complete the tangential arm assembly restoration.

A lot of that was taken care of in the previous post for this restoration.

Continuing from there I disassembled and cleaned the tonearm lowering damper, then lubricated it with some PMX-200 silicone liquid and replaced the gasket of the piston.

While the floating chassis was still out of the cabinet by itself, I like to do as many of the mechanical adjustments and electrical tasks that are possible in that state.

The following photo shows the replacement of the platter detection sensor lamp with the DKaudiolover.com LED lamp assembly.  The photo also shows the adjustment of the arm to arm distance (7.7 mm) and the new locking nut on the tonearm counter-weight.

I was also able to check and adjust the Beogram 4004 vertical tracking angle (VTA).
That is the angle that the stylus contacts the record groove.
With the Beogram 4004 turntables, that angle is defined in the service manual as the adjustment of the top surface of the sensor arm to the top surface of the platter.
That distance is to be set at 23 mm.

On the Beogram 4004 turntables, the platter to arm height for the VTA is adjustable because the platter height can be moved.

The Beogram 4004 platter assembly sits on a platter bearing.
The platter bearing has threads and a locking nut so the platter bearing can raise or lower the Beogram 4004 platter.  Thus altering the VTA.

Also of note, there are three adjustment screws on the platter bearing assembly that affect the tilt of the platter.

Ideally none of these require adjusting but they can be re-adjusted if necessary.

In the case of this Beogram 4004 the 23 mm platter to arm distance was good.

Next, I adjusted the arm lowering limit and the tracking weight calibration.
I adjusted the tracking weight at the zero position with the counter-weight screw.
Then checked and set the tracking weight for 1.2 grams.

For the electrical restoration of PCB 1 (main board) and PCB 8 (output board) I replaced the electrolytic and tantalum capacitors with new capacitors.  On capacitors with values of 4.7uF and less, I switched to non-polarized WIMA MKS capacitor types.  On values greater that 4.7uF I used new electrolytic capacitors.

Here is PCB 1 after replacing the capacitors.

PCB 1 contains the motor control, sensor detection and control logic (done with analog circuitry).

For the platter sensor reliability we always change the fixed resistor 1R26 to a trimmer resistor so the platter sensing signal can be dialed in better during calibration.  We also check the 1TR3 gain to see if it is at a high enough value (typically greater than 500).  In this case, the gain was below 400 so I installed a new transistor for 1TR3.  It has a gain of around 700.

I mounted the new trimmer for resistor 1R26 on the trace side of the board.
That is just temporary so I can easily set the value before moving it permanently to the component side of PCB 1.

I also changed out the two speed adjustment trimmers (one for 33.33 RPM and one for 45 RPM) to multi-turn type trimmers as well as replacing the speed select relay to a DKaudiolover.com relay assembly.

I changed the two Darlington pair, power transistors, IC1 and IC4, to new transistors (TIP102 and TIP107 respectively).
IC1 requires an added filter capacitor to lower the ripple current on the 21 VDC supply.
If there is too much ripple on this 21 VDC supply voltage, the control logic of the Beogram 4004 can behave unreliably.  I will check what the 21 VDC voltage looks like on the oscilloscope later.

Last, I replaced the capacitors, audio muting relay (another DKaudiolover.com relay) and added a grounding switch to the output board, PCB 8.

Because phono audio signals can sometimes produce a hum in the signal due to different types of phono amplifiers the Beogram is connected to, the grounding switch allows a quick option to connect or disconnect the Beogram's signal ground from chassis ground on the phone cable connection.

At this point the restored Beogram 4004 parts were ready to be assembled together to check the restoration progress.

It was time to put the floating chassis back into the cabinet.

Here again, is the cleaned up cabinet base.  It is all clean but the outline of stain from whatever the spilled liquid was in the Beogram is still visible.

The three mounting and chassis locks for the Beogram have to be installed first.

The Beogram floating chassis contains the platter and the tonearm assembly so those components move together if there is any vibration or bump against the cabinet while playing a record.

To prevent the chassis from floating during transport, Bang & Olufsen engineers created a locking mechanism that tightens down and prevents the chassis from moving.

The way it works is the Beogram chassis is suspended on three leaf springs so the chassis is isolated from the cabinet base.

The lock for the chassis is a screw with two sections.  The upper section and lower section are threaded in opposite directions so when the screw turns, the locking nuts close together (for locking) or open up (for unlocking).

This picture shows the two sections of the transport lock screw and the two different locking nuts.
The top and bottom nuts are threaded differently so they must be installed to their respective ends.

The washers for the chassis locking mechanism are convex on one side.  I have noted in the photos their orientation.

Here are the stages of installing the Beogram 4004 floating chassis beginning (upper left photo)
with the underside of the floating chassis lock assembly in place and ready for the Beogram floating chassis to be installed.

That is followed by the installation of the floating chassis and then the topside of the lock assembly.

Also part of the cabinet reassembly was the 4000uF reservoir capacitor for the AC power for the Beogram.

For that component I used the new DKaudiolover.com Beogram 4002/4 capacitor assembly.
Very nice.

I then soldered the arm lowering solenoid and DKaudiolover.com tracking sensor lamp assembly to their respective solder pads.

The last restored components I installed were the tangential arm spindle, pulley for driving the tonearm assembly.

That brings me back to the first photo in this post showing the first start play test of this Beogram 4004.

I am very pleased with the restoration so far.

The next step is to calibrate and move the platter detection circuit 1TR26 trimmer to its permanent position on the component side of PCB1 and calibrate the record tracking sensor.
I will also measure voltages and signals with the oscilloscope.

Beomaster 4400 - Australia Project - Reassembly and Power Check

Since the last update I finished the capacitor replacement tasks on this Beomaster 4400.

In addition to that, I replaced four incandescent lamps for the front panel. Those were the Overload Indicator, Power On and the two Tuning Indicators.

I cleaned the front panel along with applying some Deoxit to the four slide controls - Volume, Bass, Treble and Balance.

I also reattached the Beomaster 4400 heatsink assemblies with new SIL Pad thermal conductive material on the power transistors.

Here are the before and after photos of the IF Section PCB (PC 2).

Next is the Stereo Decoder and Indicator Circuit PCB (PC 3).

Last is the Pre-Amplifier PCB (PC4).

The next few photos show the indicator lamp replacement in the Beomaster 4400.
The front panel indicator lamps consist of a plastic base with contacts for the power wire and ground, a slot for mounting the lamp fixture (onto a bayonet on the front panel) and a socket for a 60ma-80ma lamp.

It takes a bit of patience and care to replace these lamps.

Here is the Overload Indicator lamp.

Here is the Power On lamp.

Here are the two Tuning Indicator lamps.  The flexible wire that connects power to the two lamp fixtures makes removal and insertion a little tricky.

The front panel controls cleaned up good after the Deoxit treatment on the slider controls.

The next two pictures show the Beomaster 4400 with it's circuit boards re-installed.
The photos show the SIL Pad thermal conductive material behind the transistors mounted to the heatsinks.

This is the point during the restoration where I can test that the Beomaster 4400 has electrical power.

I first plugged the Beomaster 4400 to my Dim Bulb with Variac tester.
That allows me to check that there isn't anything shorted that will draw a bunch of power and damage other electrical components.

With the Beomaster 4400 plugged into the tester, I turn the Beomaster on, then start applying AC with the variac.  I monitor the current draw of the Beomaster as well as the light bulb of the tester to see if any problems begin to appear.  That allows me to stop and shut power down if I see the beginnings of a problem.

The Beomaster 4400 powered up clean without any issues.

Assured that no shorts exist I plugged the Beomaster 4400 into a normal AC socket.

My first step was to check the power supply voltages.  I measured the +15 VDC voltage regulator output, the +35 VDC supply, the two +24 VDC, +33 VDC, -12 VDC supplies and the +-35 VDC rail voltages for the power amplifier.

Here is the +15 VDC check

Transistors 5TR3 and 5TR4 regulate +24 VDC to the Right channel tone controls and Left channel tone controls respectively.

There is a 35 VDC regulated voltage to the IF Section (PC 2).

After the the Beomaster 4400 volume and tone control circuits there is a Bessel Filter circuit just prior to the output amplifier.  That circuit uses a -12 VDC reference voltage.

The output amplifier circuits have rail voltages of +-35 VDC.

The last voltage check I made was the 33 VDC regulator circuit on the preamplifier board.

The voltage checks were all good so I performed the No-Load Current Adjustment for the Left and Right channels.  The service manual says to adjust the respective channel trimmers for 10mV to 15mV across each channel's emitter resistors.  For now I set them to 10mV.

This Beomaster 4400 is ready for some performance testing.  I will setup some of those tests for the next post.