Michigan Beogram 8002 Restoration: Final Reassembly

I left off in the previous post of this project with a broken Beogram 8002 cabinet hinge guide...for the service position hinge.

That type of break on these cabinets is difficult to repair with any reliability.

I have tried unsuccessfully to repair these before and it was the same section of the cabinet hinge that is broken on this Beogram 8002.

Without a good spare Beogram 8002 cabinet to replace this with, I had to attempt a hinge guide repair again.

This broken hinge guide presented a new challenge because it also had a crack in it.

So I had two repair steps.

One was to reinforce the broken piece that I needed to glue back onto the cabinet frame.

The second then, was to glue the reinforced piece onto the cabinet so it is strong enough to support any pressure from the metal hinge rod.

I used two glue types for this repair - Bondo Steel Reinforced epoxy and JB Weld reinforced epoxy.  The latter was used in the last fill of the broken section.

The repair effort turned out successful but the various glue steps and time waiting for epoxy to cure took a total of three days.

Here is a look at the repair scar after I was done.

It still isn't pretty but the scar is smooth and is not visible unless the Beogram is upside down.

The important thing is that exercising the cabinet open to the service position and back closed does not cause the repair to break again.

Since the service position is not something a Beogram 8002 owner will typically use, I am satisfied with the repair.

It means the internal Beogram 8002 components can be reinstalled.

Another quick cabinet problem I decided to address was the metal lid hinge damping.
The Nyogel 767A damping grease I used in the previous post did not result in a slow enough closing of the lid.  I could hear the lid when it reached the closed position.  With proper damping the lid should be silent.

I pulled the metal hinge bar out again from the section holding the metal lid to the cabinet so I could remove the lid for re-greasing.

The area highlighted in yellow is where I re-applied damping grease.

This time I used Nye Lubricants PG-44A Grease.  It is much thicker than the Nyogel 767A damping grease and the result was just what I was looking for.

Next was the re-installation of the internal Beogram 8002 components.

That meant removing my test point leads from PCB 1 and attaching the metal lid to the microcomputer assembly (PCB 2).

I put some thermal conductive tape on the uC IC.

Applied some thermal grease.

Attached the metal lid and checked that the heatsink on the lid was pressed onto the thermal grease.

Next up should be some photos of the reinstalling of the floating chassis assembly, PCB 1 and 2, the transformer assembly and the Control Panel assembly.

However, I was so concerned with the service position hinge repair that I spent all of my effort carefully installing the components and did not take any photos :-(

So instead, the next photos are after the internal components were installed.

Here is a sequence of photos I took as the metal deck lid was closing.  It shows the slow lowering of the lid that now touches down onto the cabinet silently.

I did a little polishing of the dust cover and I will now move on to some record listening to wrap this project up.

The only issues with this Beogram 8002 are a couple of cosmetic problems.
The left side front of the cabinet has some small pieces of rosewood veneer missing and the Beogram platter is not pretty. 

Again, the Beogram 8002 platter should never be cleaned with anything other than some very mild soap (if even that) and distilled water.  A pristine Beogram 8002 platter should only be dusted with a dry cloth.  Platters like the one in this project were exposed to some sort of cleaning fluid at some point and the top coating from the B&O factory has been damaged.

That doesn't affect playing records great which is what these turntables do.

Michigan Beogram 8002 Restoration: Cabinet Repairs

In the previous post on this Beogram 8002 restoration, the turntable electronics and record playing related functions were tested successfully.

Now it is time to work on the Beogram 8002 cabinet components.  

As with most Beogram 8002 turntables, the original double-sided tape that secured the aluminum platter deck, the metal lid over the tonearm compartment and the tonearm compartment panel had completely deteriorated.  All of those pieces mentioned are typically loose prior to this type of restoration.

The first step is to remove all of the old double-sided tape residue. It's not difficult but it is messy and not my favorite restoration task.

Here are some photos of the afore-mentioned components and the tape residue.

This photo notes (with a red dotted circle) that the metal spring that should be underneath the aluminum deck is missing.  The Beogram 8000 turntable did not have this spring. At least not during most of its production.  I believe the spring was added on the Beogram 8002 to remove any static electricity from the aluminum deck.

I will supply a replacement spring.

I soaked the tape residue in Goo Gone fluid for a couple of hours.

I did that with all of the cabinet components requiring tape residue cleanup.

Here is the hinge plate for the metal lid over the tonearm compartment.

Here are the loose components - aluminum deck panel, tonearm compartment panel and the metal tonearm compartment lid in soak mode.

The cleanup process involved scraping, cleaning up the messy residue goo, applying more Goo Gone and repeating.

After the residue is gone, the cabinet must be thoroughly cleaned to remove all of the residue traces.

Some of the old tape outlines could not be removed from the aluminum deck, even with a razor blade.

To re-attach everything I use VHB double-sided tape. It is more durable and should not deteriorate over time like the original double-sided tape did.  I use the RP32 VHB tape which has a thickness of 0.8 mm.  That is just high enough to connect the aluminum plate to the plastic platter frame. 

Note that I also installed a new spring (circled in red).

As you can see in the next photo, the aluminum panel fits perfectly onto the frame.

While I was working on the platter deck I decided to tackle the small rubber bumpers that are always worn down or missing from the front of the dust cover.  There are supposed to be two rubber bumper pads on the front of the dust cover where the dust cover rests on the aluminum deck.

Fortunately Danish Sound Parts supplies these rubber bumper pads.

I cleaned out the old, deteriorated rubber pad residue and inserted the new pads.

Here are the pads with the dust cover lowered onto the re-attached aluminum deck.

Now for the metal lid over the tonearm compartment.

The lid installation went smoothly but I discovered that the damper mechanism for the metal lid had absolutely no damping grease.  The lid would open and lock in the open position but when it was lowered, it just dropped down with a bang.

To access and apply the damping grease I had to remove the metal deck lid along with the damping lever.

The easiest and safest way I have found to do that is to push the metal hinge bar that holds the dust cover and metal lid to the rear cabinet frame.

I only push it out towards the dust cover side far enough to allow the metal lid to be removed.

I then use a spare hinge rod to insert from the metal deck lid side for re-testing the lid damping.

The rod is inserted for testing and removed to take the lid off for more application of damping grease.

After a few iterations of applying damping grease the lid started lowering at a slower, steady rate.

The cabinet was now ready for me to start re-installing the Beogram 8002 turntable components.

Unfortunately, I discovered the other metal hinge mechanism, the hinge between the cabinet base and top, had a broken piece for one of the hinge sections.

The red outlined area in the photo below show the broken area.

I could probably get the internal components installed with the broken hinge area if I am careful.

When the Beogram 8002 is put back together there is no activity on that hinge.

That wouldn't be very Beolovely.

I will attempt to repair the broken area using some very strong Bondo epoxy.  However, I only anticipate a 50:50 chance that will work.  Pressure from the metal hinge rod will likely be too much for the repair to hold.

Another consideration is to design a 3D printed part that spans past the broken area.  In that case, I would both epoxy the repair piece and drill holes for some screws into the plastic frame.

Of course sourcing another Beogram 8002 cabinet is also an option.

Michigan Beogram 8002 Restoration: Sensor Measurements

The Beogram 8002 from Michigan is performing very good with its turntable functional tests.

I connected some test leads to the Beogram's position sensors, speed sensor, record detection sensor and the forward servo drive signal (IC2 Pin 7).  Reference Beolover's post on the servo motor check.

Here are my test points on the Beogram 8002 PCB 1 board.

First, the position sensors (1 & 2) along with the IC2 Pin 7 output to the servo motor.

This picture shows the signals when the Beogram 8002 is doing a forward scan over the platter.

The image on the left is of the Fast Forward Scan and the image on the right is the Slow Forward Scan.

I placed a test record on the platter and measured the sensors again while playing a record.

The servo IC2 Pin 7 signal varies as the servo motor advances the tonearm assembly to track the record groove.  It does this once every revolution of the platter.

The tonearm controls worked perfectly and the Beogram 8002 record play was great.

Next I swapped out the test lead on the Position 2 and IC2 Pin 7 test points with the Speed Sensor and Record Detection test points.

The Record Detection on the Beogram 8002 is interesting compared to the Beogram 8000.
The Beogram 8000 platter is very similar to the Beogram 4002/4004 platters so the platter detection in the fixed arm just measures a series of pulses by detecting the platter ribs.

With the Beogram 8002 B&O designed a special laser engraved platter with two different sections of black markings as well as a flat gray section.

Here are the Beogram 8000 and Beogram 8002 platters side by side.

The Beogram 8002 platter design results in a different record detection signal than the Beogram 8000.

Here are photos of the Record Detection sensor measurements and the Platter Speed sensor measurements.  I kept the Position 1 sensor as a reference.

This first set of images is with the platter speed at 33.33 RPM.
I actually set the speed to 33.33 RPM to show the Record Detection sensor at the black marking level and at the gray section level.  The photo on the left shows the Record Detection sensor over the black markings.

Here is he platter speed set to 45 RPM but I only captured the signals over the gray section of the platter.

I am satisfied that this Beogram 8002 is functioning properly now.

I will play a couple of records with the components still removed from the cabinet just to test the sound and make sure the audio mute relay is working.

Then I will do the cabinet repairs and reassemble the Beogram 8002 to complete the project.

Michigan Beogram 8002 Restoration: Scanning LDR Assembly

Here is a quick update on the Beogram 8002 restoration project from Michigan.

I left off with the Forward and Reverse scanning control not able to adjust to the values specified in the service manual.

To fix that I knew I would have to replace the two LDR devices and/or the light source.

It turned out that the two LDR devices measured pretty close to each other when testing them after I removed them.  The problem appeared to be with the light source.

I removed the original incandescent lamp and installed an 5mm LED with a 3300 ohm current limiting resistor.

I also tested a couple of new LDR replacements but none of them were as good as the two original devices.

The new LED light source worked great and I was able to adjust the forward and reverse scanning voltages to very close to the target 620mV for the "off" state of the buttons.

I tested the basic Beogram 8002 Play, Stop, Forward, Reverse operations with this updated control panel and it performed just as I expect it to.

With the Beogram 8002 components opened up like this I will solder on some test wires to measure the position sensor, record detect sensor and the platter speed sensor.

Looking at those on an oscilloscope will show how healthy those signals are.

The results of those tests will be in the next post.

Michigan Beogram 8002 Electronic Restoration

The electronic restoration process for the Beogram 8002 mainly involves the two circuit boards, PCB 1 - PCB 2, the Beogram transformer module and the control button panel.

Here are PCB 1 and PCB 2.

Starting with PCB 1, here is a survey of the capacitors that will be replaced.

Pretty straight forward but I always like to pull the base off the old C27 capacitor (2200uF, 40V) and re-use it on my replacement capacitor.  The three-pronged base of the capacitor provides good support on the circuit board and is the negative terminal of the capacitor...so it is very handy to re-use on my replacement cap.

Here is a survey of the PCB 1 capacitors after I replaced them.  I like to replace all of the electrolytic capacitors 4.7uF and smaller with WIMA MKS, non-polarized capacitors (the red ones in the photo).

Next is the PCB 2 assembly.  It houses the microcomputer IC (a 40-pin device).  There is just one electrolytic capacitor on this board and it is for the +5 VDC power required for the uC device.  In this case, the capacitor is blown as seen in the photo below.

On the restoration for this board I remove the uC device first so I can replace the 40-pin socket with a newer one.  While the C1 capacitor is better exposed I replace it.

Now the Beogram 8002 uC device is re-installed.

REMINDER: Always take electrostatic protection precautions when handling sensitive electronic components such as digital integrated circuit devices.

Also, re-inserting a 40-pin device into a socket is not as easy as you might think.
The pins will never line up perfectly and care must be taken not to accidentally bend a pin while getting them all in place.

There is a lone control wire for the uC reset signal from PCB 2 that attaches to a terminal post on PCB 1.
The wire is a small gauge, shielded wire that often breaks where it solders onto the connector for the terminal post.  

That was the case on this Beogram 8002 so I added some extra support when I re-installed the wire.

PCB 1 and PCB 2 are now complete.  I will wait to re-attach the PCB 2 top lid until I do some Beogram 8002 functional testing. 

The electrolytic capacitor inside the Beogram 8002 transformer assembly is a non-polar capacitor that the Beogram requires for the platter motor to turn.  It is the starting phase capacitor and since it didn't fit on PCB 1, the engineers located it in the transformer compartment.

The value of the phase capacitor is different for different line frequencies.  In the US, where the line voltage is at 60 Hz, the Beogram 8002 phase capacitor is 27uF.

The Beogram 8002 Control Panel doesn't have any capacitors to replace but I do like to take it apart for cleaning, checking and installing a little test connector.

This Control Panel is in very nice condition.

The black plastic tabs in the photo that attached the PCB to the Control Panel frame are often broken (Who knows why).

These are all accounted for.

The highlighted module in the photo is where a single lamp and two LDR devices live.
The two large screws adjust the amount of light that passes from the lamp to each LDR.
This mechanism sets the idle voltage control for the Beogram 8002 servo motor that moves the tangential arm assembly.  The B&O service manual says to set the screws so the Forward and Reverse scanning functions are at an idle voltage level of 620mV.

These voltages feed into the positive input of the Op-amps controlling the tangential arm servo motor.
The 620mV level is the input level for the Forward and Reverse controls where they are not driving the motor forward or reverse.

When someone is pressing down on the Forward or Reverse scanning buttons a spring loaded aperture allows more light to the LDR and sends a higher voltage to the servo motor control to move the arm assembly forward (or backwards).

The adjustment of these scanning function screws is always a pain for me.
To set the 620mV level the LDR is measured to ground.
There are no convenient test points provided on the control panel and there have been times when I have wanted to check the LDR levels without completely opening up the Beogram.

For that reason I always install a little test connector that is accessible by pulling off the Control Panel.
That way the measurement and adjustment can be made at any time later.

Here are some photos to demonstrate....

The underneath side of the Control Panel is much cleaner than other Beogram 8002 units I have worked on. Very nice.

Here are my three test wires for measuring the two LDR devices.

...and here is the test connector installed and ready to use.

Everything is now complete where I can do a quick test to see if the Beogram 8002 comes to life.

I assembled all of the components on my bench with the floating chassis and plugged the Beogram 8002 in to AC power.

Happily I got the red dot on the display indicating "standby" and I observed the little wiggle of the platter as power is applied to the system.

The platter turn functions worked with both 33.33 and 45 RPM speeds able to lock in as expected.

I pressed Play and the Beogram arm assembly moved forward...Then it stopped moving.

That isn't totally unexpected during a "first power on" test.  It usually means there is a problem with the scanning LDR assembly in the Control Panel that I mentioned earlier.

Time to connect up my handy test connector and measure the LDRs.

Sure enough, the voltages for the scanning LDR devices were well over 1 V.  Too high over the 620mV level they should be at.  Of course this messes with the Beogram servo control circuit and the arm tends to stop.

I was able to adjust the LDR voltages to a level where the Beogram would operate but it was with the LDR voltage steady-state values of around 800mV.  However, that was with the adjustment screws fully opened up.

That isn't a good long term solution so I will have to return to the Control Panel assembly and do some work on the LDR devices. 

I want the LDR voltage levels to be around the 620mV idle voltage level with plenty of room for adjustment of the adjusting screws.