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Beogram Commander Remote Control: Maybe This is the Final Version!..;-)

This is a follow up to my recent post about the redesigned Beogram Commander remote control board, which now works in both (DC-motor) Beogr...

Wednesday, November 23, 2022

Beogram 6000 (5505): Installation of AC-Motor Version of Beolover Commander Remote Control

This post discusses the installation of the AC-motor version of the Beolover Commander Remote Control into a Beogram 6000 (Type 5505) that I just restored. These are the links to the initial three posts that discuss the initial condition of the unit, its functional restoration, and the restoration and exploration of the CD-4 channel pre-amplifier.

This Beogram 6000 has an original keypad that is in almost pristine condition:

An ideal case for installing the Beolover Commander! I developed it mainly as a way to protect the Beogram keypads. They tend to loose their coating if they are used with direct finger contact. So the best way to protect them is to not use them! The Commander allows full control of the Beogram without ever touching the keypad again. It even adds some more functionality: It has a programmable auto-repeat function and adds the 'spin the platter for record cleaning' that is a standard feature in later DC motor Beograms, but is absent in the AC motor versions.

This shows the the Commander system for the AC motor Beogram 4002 versions:

The Commander remote module is controlled via a paired Apple remote. The pairing function can be cancelled if so desired, or necessary for integration of the Commander into a larger remote controlled system. 

This is a summary of the Commander functions:

The main difference between the DC and AC motor versions of the Commander is that there is no keypad connector in the AC Beogram versions since their boards are mostly wired directly together. This means a connector needs to be installed on the keypad PCB before the Commander can be plugged in.

So the first step is the installation of this adapter. It is shown here:
The first step is to remove the keypad, flip it over, and then slide the PCB out. This is how the keypad looks flipped around: 

Unfortunately, the above picture shows the PCB already slid out partially. In its 'fully in' position, the alignment tab catches the machined groove in the aluminum profile to hold the PCB firmly in the proper position:
This tab is spring loaded, i.e. you can simply pull it up with your fingernails, and then slide the PCB out:

Before moving on with the process, it is a good idea to put the keypad into a secure location to make sure it does not get scratched accidentally.

For the installation of the adapter the PCB needs to be flipped over

On the left side of the PCB there are the wire terminals. This shows them magnified:
This is where the adapter needs to be installed. The first step is to create a 'corridor' free of solder through the center of all the wire tabs as shown here:
There are some wires that connect at the back end of these terminals as shown here:
Usually, there is no other way than to remove the solder from these wires when creating the flat area for soldering the adapter in place. After installation of the adapter these wires will need to be soldered in place again.
This shows the adapter soldered onto the terminals. It needs to be vertical relative to the PCB and the end of the white socket needs to be about flush with the boundary of the PCB. Like so:

I usually tack the adapter to the PCB on two of the terminals and make sure it is well aligned. Then I solder the remaining pads together. It is difficult to remove the adapter once it is fully soldered in. So better make sure it is in the right place before putting all that solder down.

The next step is the installation of the Commander board. This shows it from the bottom:
The part that connects to the main PCB is the narrow tab on the right side. The raised edge on the far right end aligns the board with the edge of the main PCB. The bolt hole on the left side is used to bolt it onto the main board using the threaded hole that is used for the right PCB screw of the main board. It is located between the two blue trimmers I installed for adjusting 33 and 45 RPM.
This shows the Commander board in place. The original PCB screw needs to be replaced with the included M3x14mm screw due to the added thickness of the Commander board.:
It is important that the black remote receiver is fed in between the the plinth and the enclosure next to the front alignment feature of the plinth.
Once the board is bolted in, the keypad can be connected with the included white jumper:
This shows the connection to the Commander board in more detail 
and this the connection to the adapter board
It is important to note that the installation of the white jumper needs to be done carefully, since it is easy to bend the filigrane contact pins inside the sockets. In other words, the connectors need to be aligned properly before they get pushed in. This shows everything from the top:
Now the keypad PCB can be slid back into the keypad profile:

The final step of the installation is mounting the auto-repeat indicator PCB under the screw that holds the keypad in place. Since this is a Beogram 6000 which uses the CD-4 indicator integrated in the RPM panel, I had to modify the little PCB by cutting out a corner with sheet metal shears. This opened a path for the light emitted from the CD-4 indicator LED under the keypad.

After this I put everything back together and tested the Commander system. I selected one of my favorite Bob James albums, 'Lucky Seven' from 1979 (Tappan Zee Records, Columbia, JC36056). Of course this album was thoroughly cleaned with a CleanerVinyl ProXL setup using a multi-frequency ultrasonic cleaner before listening! This shows the Beogram 6000 in action together with the nice cover of this album: 
Beolovely! Soon it will be time to return this Beogram 6000 to its owner in the UK.

Thursday, November 17, 2022

Beogram 6000 (5505): Full Functional Restoration Pt.2: Exploration and Restoration of CD-4 Pre-Amplifier

This post is the second installment of my report of the restoration of a Beogram 6000 Type 5505 with AC platter motor. The first part can be found here

What distinguishes a Beogram 6000 from a Beogram 4002 is that it has a CD-4 capable quadraphonic pre-amplifier board factory installed. In many Beogram 4002 such a board could be installed at a later point. CD-4 is mostly interesting from a historical point of view, since this 4-channel format never really took off, and there are not many CD-4 vinyls in circulation.

However, the 6000 has an on-off switch for the CD-4 detection feature, and in off position this pre-amplifier becomes a standard RIAA pre-amp for stereophonic records. This allows connecting a 6000 directly to any standard high-level line input. Many modern receivers do not have a dedicated Phono input anymore, and so getting a 6000 is an interesting option if a classic and/or internal pre-amp design is preferred.

This shows the CD-4 board installed after removing the keypad:

Now that is a pretty 'complex' board! It even has a little board piggy-backed on the part that is located above the keypad. Nowadays a circuit with such functionality would be a single chip with a few external passive components and a power supply. 

Let's have a brief look at the circuit diagram first, the discussion of the restoration follows below. I made an annotated version while trying to understand 'what is what', and which parts are important for the use as RIAA stereo pre-amp.

Here we go: click on the pic and you should be able to see the high-res version and be able to read my comments. Be aware that the comments reflect my 'current state of knowledge' about this board, and should therefore be taken with a grain of salt.

The purple marked/annotated parts are the essential components of the CD-4 detection and demodulation system. The green path is the RIAA stereo signal path through this board. An introduction to CD-4 published in 1973 by JVC can be found here.

In a nutshell, the CD-4 format uses a bandwidth of ~20 to 40kHz to carry two stereo signals, front and rear, which each need ~15kHz bandwidth for high fidelity. It is obvious that a faithful reproduction of frequencies as high as 40kHz requires a high-quality cartridge with a low mass cantilever. The MMC6000 cartridge was dedicated to this format. It has a beryllium cantilever. I think a later MMC20CL with sapphire cantilever could probably also be used. But not sure.

Since we only have one groove, but two sets of signals the signals are encoded as 'sum signal' Front+Rear (F+R) in the audible part of the bandwidth and 'difference signal' Front-Rear (F-R) in the >20kHz range. The F+R signal is pre-emphasized in accordance with the RIAA curve and essentially 'put into the groove' like a conventional stereo signal. For this reason CD-4 records are compatible with standard stereo players. One just does cannot distinguish the rear channels.
The F-R signal, in contrast, is not pre-emphasized, and it is superimposed to the F+R signal as a frequency-modulated signal around a 30kHz carrier tone. Sort of like a FM radio signal, just with a carrier that is much closer to the modulated audio signal. Due to the high-frequency bandwidth of the F-R signal it is much more affected by noise from the vinyl surface and preamp etc...This made it necessary to use noise-suppression for this signal. This is done with a system that works similar to Dolby used on tape decks. JVC called their system ANRS. The principle is similar to the Dolby systems: the volume range is compressed for recording, and then decompressed during play. This reduces the noise level for low-volume sections.

Let's see what happens with the signal from the cartridge in the circuit:

The diagram shows only the left channel, as well as the circuitry that is used by both channels. The signal from the cartridge enters the circuit via the coupling capacitor 6C2 into the opamp 6IC1. There it receives a 40-50dBV boost and is also RIAA de-emphasized in the low frequency range via the filter 6C1 and 6R5 in the feedback circuit. This does not affect the high-frequency F-R part of the signal, therefore it can be done for the entire signal right in the opamp. 

After the opamp, however, the signal gets split up into F+R and F-R.

1) F-R:
After the opamp the signal goes through a band-pass filter to get rid of F+R and then enters a demodulation circuit (annotated purple) that works similar to a FM radio receiver followed by the ANRS noise reduction decompressor. At the end of the process the F-R signal is reconstituted in the audible spectrum ("B" in the diagram) and enters the "matrix" where it is combined with the F+R signal and then F and R are spit out separately. The matrix does this by adding the F-R signal to F+R and also  the inverted (180 deg phase shifted) F-R = -F+R signal to F+R. So we get F+R+F-R = 2F and F+R-F+R = 2R. All of this of course in stereo. So at the end we have the front channels FR and FL, and the rear channels RR and RL.

2) F+R:

After the opamp, the signal is also sent through a low pass 6R7/6C4 which does the second half of the RIAA deemphasizing. This path is marked green. The signal then goes through the decoupling capacitors 6C31 and 6C32. In between the two capacitors the signal is diverted into a filter formed by 6L4/6C33/6R47 which essentially removes any trace of the F-R signal, and then feeds the F+R signal into the matrix for reconstitution of separate F and R channels.

What happens with a conventional stereo signal?

If there is only a stereo signal from a conventional record, the signal is routed further along the green path, which basically sends the signal unmodified to the output socket. Of course it also goes through the filter and the F+R section, but in the case of regular stereo the matrix signal is stopped via the diode switch es from reaching the output socket - see below.

How does the circuit make sure that a regular stereo signal does not get messed with in the matrix circuit?

This is basically done by the 'diode switch' comprised of the diodes around the matrix. Depending on how these diodes are biased the signal either travels the green path or the decoded CD-4 signal gets routed to the output socket.
The diode switch is controlled by the "frequency-to-DC-converter" (blue frame on the left) and the Schmitt trigger circuit (red frame next to it). Basically, the frequency-to-DC-converter produces a DC output voltage at the emitter of 6TR1 that is low (0V) if there is no CD-4 carrier tone, and high (3.8V) if there is one. This signal then gets fed into the Schmitt trigger which has two outputs A and B. If CD-4 is detected A is high and B is low, while if there is a regular stereo record we get the reverse output.

Both A and B low mutes the entire output. This is done via the muting circuit, which essentially overrides the Schmitt trigger by pulling both outputs A and B low via 6D17 and 6D18 when the arm is up.

The great thing (for using it as a regular RIAA pre-amp) about this circuit is that, with the CD-4 switch on the right side of the Beogram enclosure (added in red to the frequency-to-DC-converter circuit), one can pull the base of 6TR11 permanently to GND. This configures the Schmitt trigger permanently to its no CD-4 setting, B=high and A=low, and then all records are played like stereo records. In other words the signal follows the green route. While this should happen automatically, I think B&O added the switch to make sure one can set the patch to regular stereo incase there is a 'misunderstanding' in the detection circuit. After all we are talking about a 'complex analog audio system'...;-).

Restoration of the board:

This shows the board after extraction:
And here the upper section after removing the piggy-backed smaller board:
I replaced all the electrolytic capacitors on the board. The ones in the 'stereo signal path' were replaced with fitting WIMA foil capacitors to reduce distortions: 
Pretty! They know exactly why they package them in these pretty red little boxes!...;-)
I also replaced the CD 4 indicator lamp with a LED. If you use a high output LED that only needs a small current to light up, then you may want to add a ~3k resistor between the base of 6TR14 and GND to pull the base down sufficiently to turn the lamp off when there is no CD-4 signal/the switch is turned to OFF. I did that with a SMD resistor on the solder side of the board at a convenient location that could be bridged by the resistor. The blue resistor seen in the picture is the current limiting resistor for the LED to make it compatible with the 22.8V rail:
This shows the restored board
and the removed parts.
Quite a few electrolytic capacitors in this historic analog design! While in there I also added a switch in the back allowing connecting the output cable shield to the signal ground in case there is a hum issue:
This is where the other end of the switch connects at the output plug. I added it to the pin where the inner braid is connected:
This shows the board installed again:
After this I put the keypad back in place and did some listening. Unfortunately, I was able to hear some motor noise in the speakers when cranking up the volume with the arm down next to the platter.
Not too unexpected in a design like this since motors introduce a lot of noise on power rails, while the RIAA amp is very sensitive to small signals.

This was confirmed by a measurement with my Quant Asylum QA400 audio analyzer. The red trace shows the noise spectrum with the arm down after I put the Beogram back on the bench (note that this spectrum is shifted 20dBV higher to separate it from the blue spectrum that was measured after my fix was implemented). Most of these peaks, except the one at 60Hz come from the motor.
I hooked up the oscilloscope to the 30V rail (orange wires on 3300uF capacitors) and saw this (using AC coupling):
~500mV noise!

So I did two things:
First I converted the power supply of the CD-4 board from 'main PCB 22.8V rail referenced' to a 24V Zener reference. This is easy to do on this board. This shows the original power supply section of the board. The big capacitor is 6C94:
I removed this capacitor and implemented a 24V Zener diode in its place. In combination with 6R96 and 6R98 this created the classic Zener voltage divider to be fed into the base of an emitter-follower like 6TR17. One more thing had to be done to 'disconnect' the blue wire that is the 'reference' to the 22.8V rail of the main board. I did this by removing 6D20 while leaving the blue wire in place. This shows the section in its final configuration:
The second step I took was to implement a 'capacitance multiplier' in front of the two 3300uV reservoir capacitors:
Basically, at the positive terminals of the capacitors the orange wire from the emitter of 0TR1 feeds the regulated voltage to the capacitor. In the original configuration, a second orange wire then connects to the rest of the circuit. In my modification the orange wire now connects to the output of the capacitance multiplier and the input to the capacitors.
This is how the voltage looked after the added circuit:

Much nicer! And when I measured the noise spectrum, I got the blue trace in the above graph. You see that most peaks are gone. Only the usual 60Hz interference and a couple smaller peaks are left. 

How does a 'capacitance multiplier' work? Essentially it is a bit of a misnomer, since it is rather an emitter follower that is referenced to a very low pass filtered (2k/100uF) low-current version of the original to be cleaned up voltage rail. Since the emitter follows the signal at the filter output, it removes all the high frequency stuff on the power rail. There is a great Dave video on the EEVblog that explains all the ways to remove ripple and noise. I built it with a TIP102 Darlington to get a big gain, which allows to reduce the cutoff frequency even more since the current in the filter output can be very small while still being able to drive a large current to the load. This shows a simulation of my little circuit in iCircuit:
I assumed a 40V DC signal with a 1Vpp ripple on it (green) and a 1000x gain for the transistor, similar to a Darlington. The circuit cleaned this up to the yellow trace which has a 13mV ripple. So basically a two magnitudes improvement.

I listened to the deck again, and only a healthy RIAA pre-amp hiss came from the speakers when cranking up the amplifier with the arm down next to the platter! Beolovely!

My final act was to try measuring the total harmonic distortion (THD) and THD+noise (THD+N) of this RIAA amplifier using the QA400, which can calculate it from the FFT spectrum. THD numbers are always a bit ambiguous when reading manufacturer specifications since it is never stated under what conditions they were measured. So it may be difficult to directly compare my measurements with others. Therefore, I post the spectra that I measured along with the calculated numbers. 
The QA400 outputs were connected with a BNC-to-minigrabber cable directly to the Left and Right Channel pins at the input plug of the CD-4 board. Then the deck was turned on at 33 RPM and the arm lowered to open up the signal path through the diode switch. The CD-4 switch was set to OFF. 
I did two measurements for two input levels, -60dBV and -70dBV. These levels correspond to 14mVmax/10mVrms and 4.4mVmax/3.16mVrms respectively signals. I measured a few MMC cartridges a while back and they produced such levels during fairly loud passages.
The first graph shows the -60dBV curve. Right and left looked fairly similar, so I am only showing the right one for clarity. The signal strength of the amplified 1kHz tone is about -17dBV, i.e. we have an amplification at 1kHz of about 43 dBV. This gain resulted by setting the two gain trimmers in the opamp feedback to center position. For this spectrum the QA400 calculated THD=0.46% and THD+N=0.52%.

The second graph shows the same measurement at the lower -70dBV input level. It is obvious that the harmonics went down, and consequently the THD numbers are lower with THD=0.14. THD+N=0.8 is higher since the signal to noise ratio is now 10dB worse.
These THD values are considerably higher than what is stated for modern external RIAA pre-amps, which usually seem to be in the 0.0X% range at similar gains.
In my opinion this does not matter much since cartridges and the records themselves usually have much higher distortion levels, i.e. the small amounts added by this classic RIAA design will not matter much. I really like listening to this Beogram 6000. It sounds very nicely and gives you that awesome 1970s warmth that makes you think of bellbottoms and brown corduroy suits with wide lapels!...;-)

Wednesday, November 16, 2022

Beogram 8000 Type 5613: Wisconsin project is ready for record play

I finished the service manual checks and adjustments on this Beogram 8000 turntable.
The power supply voltages look good. The forward/reverse scanning LDR adjustments are set.
Tracking force is calibrated as well as the record tracking sensitivity.

A quick workshop test play of a record shows that the Beogram is ready for some record play listening tests so I will install the components back into the Beogram cabinet and enjoy some records.

Here are the supply voltage checks at the filter capacitors and at the output of the regulators.
From left to right are +15 VDC, -15 VDC and +5 VDC.

In this photo I show using my little three pin test connector for adjusting the forward and reverse scanning sensors (LDR devices).  I like to set the idle voltages for these around 650 mVdc.

Next was calibrating the tonearm tracking force at the 1.0 gram mark on the adjustment scale.
I adjusted the counterweight at the back of the tonearm until the 1.0 gram mark on the adjustment scale measured 1 gram on the scale.

The final adjustment is for the record tracking sensitivity.  This is the adjustment where the P4 connector is disconnected from PCB 1 so the platter doesn't turn.  

The procedure calls for manually turning the platter with a test record.  The stylus is dropped onto a track in the middle of the record and the tracking sensor sensitivity is adjusted so the tangential arm servo begins advancing the tonearm assembly between 1 or 2 revolutions of the platter.  After that the servo motor should advance the arm every revolution of the record.

After a few iterations of the adjustment screw the sensitivity was set.

Before putting the Beogram 8000 all back together in its cabinet I wanted to listen to a couple of records on it while it is in the workshop.  I connected it to my Workshop Beomaster 8000 and gave it a listen.  Using the Beomaster 8000 also tests the remote control functionality between the Beogram 8000 and the Beomaster 8000.

The MMC-20CL cartridge played beautifully on the Beogram.  My Beomaster 8000 is connected to a pair of Beovox S75 speakers and did their part in the record play enjoyment :-)

Note: I keep my Workshop Beomaster 8000 opened up all of the time. It is fully functional where I can use it to listen to music while I work but it is always available to perform board testing with and that is its main purpose in the shop.

Monday, November 14, 2022

Beogram 8000 Type 5613: Completed restoration tasks on the Wisconsin project

In this post I will go over the various Beogram 8000 restoration tasks that I completed.

As we often do with Bang & Olufsen linear tracking turntables, I started with the floating chassis.
There are only a couple of capacitors to change out on the Beogram 8000 floating chassis but there are quite a few other tasks.

Besides replacing capacitors 0C1 and 0C2, I check the platter hub tachodisc, replace the phono signal muting relay, clean and lubricate the tangential arm assembly, perform some early stage service manual adjustments and replace the servo motor belt.

I will start by showing the removed floating chassis again.

This Beogram 8000 is missing its serial number information but I can tell from the missing factory modifications and the version of the platter speed sensor that this is an early serial number Beogram 8000 unit.

However, it already has its tachodisc upgraded from the original plastic tachodisc to the B&O metal disc.

The phono audio muting relay (in the DIN plug housing) is the National type so I replaced it with the Beolover replacement relay component.

As I mentioned above, this is an early serial number model and the 0C1 capacitor for the +5 V regulator is not the 1 uF value that later Beogram 8000 units had installed.  I upgraded 0C1 to 1 uF.  I also swapped out 0C2 with a new 47uF, 10 V electrolytic capacitor.

Next, I partially disassembled the tangential arm assembly for cleaning, inspection and lubricating.

Inspecting the underside of the tonearm assembly I examined the arm lowering components for dirt and any obstructions. 

The Beogram 8000 tonearm lowering operation can sometimes drop the arm suddenly from the raised position to a record.  The causes of those faults can be due to metal on metal contact between the back (underneath part) of the tonearm and the tonearm height adjustment screw. Over time the arm wants to stick to the screw instead of lowering.  When the arm lowering lever moves to control the slow descent of the arm to the record, the tonearm stays behind (seeming stuck in the raised position).  The weight of the arm finally overcomes the problem and the arm drops...but without any control over the lowering.

This type of problem can be corrected by placing a thin piece of non-conductive material between the back of the tonearm and the tonearm height adjustment screw.  I like to use a small piece of Dura-Lar (made by Grafix).

I used a little bit of epoxy to keep the Dura-Lar in place.

Because the bottom of the Beogram 8000 tonearm is easily accessible during this stage of the restoration I like to perform the adjustment for the height of the fixed arm from the surface of the platter and the alignment of the tonearm to the fixed arm. 

Tonearm adjustments for a lot of turntables is a very involved process.  Bang & Olufsen has always strived to make that relatively painless.  Granted, part of what makes a Beogram easier to adjust is the fact that the phono cartridge is integrated into the tonearm.

On the Beogram 400x turntables the platter height is adjustable and the service manual specifies a required distance of 23 mm from the platter surface to the top of the fixed arm (and tonearm).
In that adjustment the platter is actually raised and lowered to achieve that distance.
The 23 mm is the B&O calculated height to achieve a vertical tracking angle (VTA) for proper record play by the B&O MMC cartridge.

On the Beogram 8000 the service manual also specifies a distance of 23 mm from the platter surface to the top of the fixed arm (and tonearm).  However, there is no adjustment of the Beogram 8000 platter assembly to alter that distance. A small screw on the fixed arm can adjust the position of the end of the fixed arm (to the platter) but the mounted position of the fixed arm and the tonearm (at the pivot point of the tonearm) is not adjustable.  So the vertical tracking angle (VTA) on the Beogram 8000 is built into the tonearm design and the tonearm pivot point is fixed for the correct VTA.

The adjustment of 23 mm for the end of the fixed arm to the platter surface and the corresponding alignment of the tonearm to the fixed arm (the horizontal parallelism) are for cosmetic purposes.
I suppose the 23 mm distance at the end of the arm also ensures that the stylus does not hang too low when it is scanning a record.
The screw on the fixed arm and on the underneath side of the tonearm are for adjusting the ends of the arms from the platter surface...not the height of the tonearm at the arm pivot point and not the vertical tracking angle.

It is important to perform this adjustment per the service manual though, as the goal of the restoration is a properly functioning and proper looking Beogram 8000. 

To perform this adjustment I install the Beogram 8000 tangential arm assembly on the two guide rails but leave the position spindle off.  That allows me to manually slide the tangential arm assembly over the platter without having the Beogram 8000 fully assembled and working.

Once the end of the fixed arm is at a height of 23 mm from the platter surface, the tonearm height adjustment screw can be used to align it (the horizontal parallelism) with the fixed arm. 

The Beogram 8000 floating chassis can now be reassembled with a new servo motor belt and I can move on to the electronic restoration tasks. 

I will leave the tracking force adjustment and record tracking sensor adjustment until I have the electronics portion of the restoration complete.

For the electronic restoration I started with the Beogram 8000 processor assembly, PCB 2. 
That is the circuit board inside the metal shield box that attaches to the main board.

There is only one electrolytic capacitor on PCB 2.  That is 2C28 which is a filter capacitor for the +5 V power to the board.  

In this Beogram 8000 PCB 2 the 2C28 is easy to get to.  There is normally another small add-on board (8005065) covering it.

That brought up a decision that I had to make about this restoration.

Because this is an early serial number Beogram 8000 it sends the speed sensor signal directly from the operational amplifier (op-amp) on the main board (PCB 1) to the processor (uC) on PCB 2.

Later serial number Beogram 8000 units and all Beogram 8002 units have a small add-on board containing a flip-flop circuit that the speed sensor signal is sent to first...before going on to the uC.
The flip-flop is clocked by the same clock as the uC and makes the speed sensor signal a cleaner rectangular waveform.  B&O added this flip-flop circuit to fix periodic variations of turntable speed.

Here is the B&O modification description from a later Beogram 8000 service manual.

I decided that this modification really should be applied to this early serial number Beogram 8000.

Note: In fact, I returned to my previous Beogram 8000 project from Houston and installed it there as well.

I removed the uC IC from PCB 2 first, along with the 40-pin IC socket.
I always do that anyway on a Beogram 800x restoration because I like to install a new 40-pin socket.

With the 2C28 capacitor and the big uC IC and socket out of the way I have a lot more room to install the speed sensor signal modification per the service manual.

I also measured the old 2C28 capacitor.  The 47uF value was just barely out of tolerance.

For my implementation of the speed sensor signal modification I started by removing the 4.7nF ceramic capacitor 2C25.  

Then I cut the copper foil trace between connector P6-2 and the uC IC (2IC1) pin 40.

Now the speed sensor signal from P6-2 will be re-routed to the add-on board as the input to the flip-flop (2IC3 pin 5).  In keeping with the suggested color code I will use a yellow wire for that connection.

First, I have to de-solder hole "C" in PCB 2 and expand its diameter a bit with a hand drill.

Then I could install a yellow colored wire from P6-2 through the hole "C" for routing to the add-on board.

I prepared the wires for the add-on, speed sensor signal conditioning board.
Per the service manual instructions, the blue wire is for ground, the red wire is for +5 V, the green wire is for the clock and the orange wire will deliver the speed sensor signal back to the uC (2IC1) pin 40.

Here is PCB 2 with the new add-on board, a new 2C28 capacitor and a new 40-pin socket (for 2IC1) installed.

...and here is 2IC1 installed in the new socket.

PCB 2 is ready to go so I continued on with the board restoration of PCB 1 (the main board ... that hosts PCB 2).

Here is the before photo of PCB 1 by itself.

Here is PCB 1 with all of the small electrolytic capacitors replaced.  Only the three larger ones remain to be added.  While the board was in this stage I turn it over and re-flow the solder on all of the board connector pins.  It is well known that those connections can develop hairline cracks.  It is also a good time to inspect all of the traces for any breaks.

As I like to do, I removed the ground mounting ring from the original 1C27 (2200uF, 40V) capacitor and reuse it on the replacement 1C27 capacitor.

That completes the PCB 1 restoration work.

Next up is changing capacitor 4C1 inside the Beogram 8000 transformer assembly.
4C1 is a bipolar capacitor for the Beogram 8000 platter drive motor.
Its value varies depending on the line voltage where the Beogram is used.  
The Beogram 8000 is fitted with a fixed transformer for the country's voltage it is made for.
For example, Europe's line voltage is at 50 Hz while the voltage in the North America is 60 Hz.

The value of 4C1 for a 50 Hz line voltage is 39uF but for a 60 Hz line voltage it is 27uF.

Since this Beogram 8000 is North American model I replaced 4C1 with a 27uF capacitor.
I haven't found a good non-polarized capacitor for that value so I put two 56uF capacitors in series (with their negative leads connected together).  This results in an acceptable 28uF.

The last step of the electronic restoration tasks is to add a test connector to the forward and reverse scanning sensor buttons in the control panel.  I like to be able to check and adjust the sensitivity on the scanning sensors without having to open the Beogram 8000 back up.  Adding a little three pin test connector lets me connect a multi-meter for testing by just opening up the control panel plate.

All of the initial restoration steps are now complete and I can assembly the floating chassis components with the electronic components for a quick test. 

I haven't set the record tracking and tracking force so I won't try actually playing a record yet...but I can test the platter speed detection, record detection and scanning functions.

Those are the results I wanted to see.  Everything looks great so far.

In the next post I will check power supply voltages, adjust the scanning sensitivity, tracking sensitivity and tracking force.  After that I can test play the first record.