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Beolover SyncDrive: DC Platter Motor Replacement for Beogram 4002 and 4004 (Type 551x and 552x)

Late Beogram 4002 and the 4004 (Types 551x and 552x), which have DC platter motors instead of the earlier synchronous AC motors usually suff...

Thursday, September 30, 2021

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) Beogram 4002 and 4004s. The first batch still needed a few 'improvements'. I guess there is never a first iteration of a circuit board design that works right away...;-).

I just received a first batch of the revised (again) boards and also the correct jumper wires (the first batch had the plugs oriented in the wrong direction due to a miscommunication). This shows the updated Commander kit:

I made a new YouTube video. It introduces the latest version, demonstrates its use, and shows in detail how to install it (no soldering required!):


Tuesday, September 28, 2021

Bay Area Beogram 8002: Cabinet Work Completion to First Record Play

Today I finally got this Beogram 8002 turntable into a listening room to begin record play testing.

It took a little longer than I anticipated to finish up the reassembly to arrive at this point but I took a little detour to fix the chipped rosewood trim on the front panel.

A cosmetic repair of the trim was not originally in the plans for this restoration but the more I looked at it the more I didn't like leaving the front panel chipped like that.

The journey down the path of repair for something like this can end up taking extra time of course and this one certainly did. When working on repairs like this glue is involved so that means waiting time for glues to cure.

Then there are times where it takes more than one attempt to make the repair. That also happened here.
In my initial repair attempt I decided to just try and patch the areas that were chipped. In this case two...a large chip and a much smaller one.

The fit and install of the patch for the larger chip went well. I used a piece I cut out of some rosewood veneer I keep for this type of repair. The fit and pattern match was good.

After gluing the repair patch in place I cut off the excess, sanded the repair and applied some boiled linseed oil for a finish.

It should have been a nice repair but the small patch turned too dark and I realized that the small remaining chip was too small to make a good repair. Even if I just used some wood filler.

It didn't look terrible and was better than having the chips there but I decided I couldn't leave it like this.
The large patch fit good but darkened too much and my eyes kept being drawn to the small chip that still needed to be fixed.

My rework of the fix was to cut out the first repair attempt and make the cut so that there would be just one, rectangular patch piece needed to cover both of the original chips.

I selected a lighter section of rosewood from my veneer piece in the second attempt. 
Here is the result of the second (and final) attempt.

The patch piece still darkened but I think overall this patch is much better.  It is far from perfect but better than the original chips.

As a side note...I investigated using some rosewood trim from a spare Beogram 800x turntable cabinet that was beyond repair.  I also looked at some spare Beocord 800x and Beomaster 6000/8000 cabinets for possible donor trim pieces.  In all cases the cabinets I have in my spare parts collection are all darker than the rosewood trim on this project. So my veneer piece is as good a match as I could get.

Returning to the tonearm compartment, I installed the nice, clean replacement hinge piece for the lid.
I used kilopoise grease for the lid damping and temporarily held the hinge in place with the original hinge bar for this Beogram.

The Beogram 8002 cabinet is now ready to start all of the reassembling of its components.

The first steps were to put the main turntable components (circuit board, transformer, control panel and floating chassis) back into the cabinet.

I like to do that first because until those are in place I can't close up the two halves of the cabinet and I don't like having that loose when I work with the dust cover and tonearm compartment lid.

In my haste to do the reassembly I neglected to photograph the re-install steps this time but for reference, here are the install steps from the last Beogram 8002 project.

Here is this Beogram 8002 with its internal components installed and ready for the dust cover and tonearm compartment lid installation.

For the dust cover installation I prefer to secure the dust cover and tonearm compartment hinge assembly together with the Beogram 8002 bar hinge.  By removing the bar hinge at the beginning it saved me from removing the back plate of the cabinet that has the hinge bar mounts for the cabinet frame. Removing that plate can often result in a loose rear plate because it has plastic clips that easily break off.

After I had the dust cover and tonearm compartment pieces secured with the Beogram 8002 bar hinge I attached the dust cover damping spring assembly.

Here is the dust cover installed and with the damping spring set properly to allow slow lowering of the dust cover.

The dust cover has two rubber bumper pads that mount in the front part of the lid (where it rests when lowered all the way to the deck). Those rubber pieces are always deteriorated and broken off.

I cleaned out the original bumper pad residue and installed my own 3D printed bumpers.

The dust cover now becomes an alignment guide for installing the tonearm compartment lid.

I used the same 3M VHB double-sided tape on the tonearm compartment lid as I did for the Beogram 8002 metal deck.

Everything looks like it is installed and this Beogram 8002 is ready to play some records.

It is off to my office where I can listen to records on this Beogram while I work.
Tonight I was in the mood to hear some nice jazz recordings so I broke out Quincy Jones "Walking In Space" and Lonnie Liston Smith "Live!".  

Don't stay up.  These listening tests may take a while.

Wednesday, September 22, 2021

Bay Area Beogram 8002: Some cabinet work

The Beogram 8002 turntable components are ready to go back into the cabinet but the cabinet is not quite ready.

This Beogram's cabinet is in pretty good shape but there were a few issues that had to be resolved as noted in the initial assessment of this unit.

I pulled apart the aluminum deck lid first as I didn't like someone's previous re-attachment of it.
The double-sided tape they used is too thick and has too much play in it.  The tape looks like the kind used for window and door insulation.

I applied Goo-Gone on all of the surfaces that had tape and glue residue that needed removal and let it sit overnight.

With the metal deck off I discovered the little metal spring that should be there was missing.
The original spring must have got lost in the original deck attachment attempt. 
I will have to use a spare one.

The spring is there to prevent any static charge from building up on the metal deck.

Here are the pieces with the old tape and glue cleaned off.

For reference, here are the dimensions of the missing spring.

Here are the new 3M RP32F VHB tape pieces in place on the deck along with the replacement static discharge spring.

I like this double-sided tape for the Beogram 800x deck because it is good, heavy duty VHB type tape that is easy to use and is 0.81 mm thick.  It makes for a good re-attachment and the seam is as close as it can be.

Here is the metal deck re-installed.

You can see in that last photo that there is a small nick in the rosewood trim on the front of the cabinet.
I will try to make that less noticeable with a small sliver of rosewood veneer I keep around for this type of restoration.

Another Beogram 8002 cabinet piece that had double-sided tape that required replacing is the metal deck lid in the the tonearm compartment.

I used VHB tape for that re-attachment as well but it is some 1 mm thick tape.

Here is the tonearm compartment deck lid back in place for a test fit.

There is a small metal bracket that fits on the dust cover where the damper spring assembly fits onto.
It is for damping the lowering of the dust cover.

The bracket was originally attached with the same double-sided tape B&O used for the metal deck so it will eventually deteriorate and fail.

I cleaned off the old residue and used epoxy to re-attach it.

I used the bar hinge of the Beogram to make sure the bracket was aligned properly during the glue process.

I set some weight on the bracket so the epoxy would set properly and will let that cure for 24 hours.

There is another cabinet piece issue to be addressed on this Beogram.
The tonearm compartment top lid.

This Beogram arrived with the hinge lever for that lid broken.
It appears to have had an attempt made before to repair it.
You can see glue residue from the repair attempt.
That isn't really a good sight plus it could interfere with the bar hinge.

Here is a possible replacement lid.  It has its hinge lever intact.

That hinge lever fits into the slot on the cabinet that has a mating lever piece to control the raising and lowering of the lid.

There is a cavity where the levers connect that is supposed to be filled with Kilopoise damping grease.
Most of the damping grease is gone from this Beogram unit so I will have to refill the compartment with new Kilopoise grease.

Tomorrow the epoxy for the dust cover damping spring bracket should be fully cured and I will be able to start reassembling the turntable parts into the cabinet.

Wednesday, September 15, 2021

Bay Area Beogram 8002: Oscilloscope Measurements

This post is a wrap up of the functional testing on this Beogram 8002 turntable.
For my own reference between various Beogram 8002 turntables I like to collect oscilloscope photos of key Beogram signals.

Here is a photo of my test leads connected to the main board of the Beogram 8002.

I have test leads for six Beogram 8002 signals -

Position Sensor 1 (the position of the tangential arm assembly)
Position Sensor 2
Detector Arm (the signal from the sensor in the fixed arm)
Speed Sensor (the signal from the platter speed sensor)
Servo Motor Forward
Servo Motor Reverse

My oscilloscope has four channels so I will just monitor what is happening on the servo motor and the position sensors first.

As a reference, here are the signals when the Beogram 8002 is parked in the Standby mode.

Pressing the Play button drives the Beogram tangential arm assembly forward and disengages the SO switch.
Notice there is a designed delay from when the SO switch disengages and the position sensors start to cycle.

The servo motor advances the tangential arm assembly and detects a record on the platter.  The servo slows down the advance as it reaches the set down point and stops to lower the tonearm.

Once the tonearm sets down the servo will advance again as the tonearm moves through the lead-in groove of a record.

There will be periodic activity on the position sensors and servo forward voltage as a record plays and the Beogram keeps the tonearm tangential to the record. The position sensor signal pulses will vary depending on how much compensation the servo motor is told to adjust for by the tracking sensor.

When the end of the record is reached the servo motor moves the tonearm through the run-out groove and stops. The motor reverses and begins the return of the tangential arm assembly back to the Standby mode position.

The reverse to home (or Standby position) can also be initiated during record play by pressing the Stop button.

Another action that results in a return to the Standby position is when the fast scanning button is used to move the tonearm forward until the maximum forward position is reached. 

The Beogram 8002 servo control drives the tangential arm assembly back to home where the SO switch is engaged.

To look at the platter speed sensor and the arm detector sensor I swapped out those test leads with the two oscilloscope leads I had been using to monitor the servo motor.

I will just show one photo with these connected. 
This photo shows the Beogram scanning for a record.  The position sensors show the tangential arm assembly is moving.  The speed sensor shows that the platter is rotating (at 33.3 RPM) and the arm detector sensor is showing pulses that indicate there is no record on the platter.

Next I changed two of the oscilloscope probes to measure the forward servo motor command and the Beogram tracking sensor. 
That meant adding the Tracking Sensor signal probe wire to the main board.

Looking at the basic turntable functions again with the tracking sensor being monitored gives these photos.
Note: Keep in mind that the Tracking Sensor signal is the tonearm movement away from its tangential position with the record play path. When that occurs the Tracking Sensor signal increase results in the forward motor drive to increase.

The following picture is the same scenario as the previous one except this is set to capture the first second of the press Play button event.  The position sensors don't begin counting until about 300 milliseconds after the tangential arm assembly starts moving.

This picture is of typical record play events over a 12 second period.

Finally, this is a picture of the end of record run-out groove event.

I am ready now to do some minor work on the Beogram 8002 cabinet and reassemble this turntable for the listening tests.