Beocord 5000 Type 4923: Tapehead cleaning and playback testing

Continuing on with this Beocord 5000 Type 4923 I am getting closer and closer to wrapping this project up.

In this post I adjusted some mechanical components and cleaned the tape heads (and rubber wheels).
I also connected the Beocord 5000 up to my WOW & Flutter meter.  

First though, the Beocord 5000 has a dedicated motor and pulley to open and close the cassette deck assembly in the cabinet.  I mentioned before that is because the Beosystem 5000 components were designed to be stacked on top of each other.  B&O engineers designed the Beocord 5000 cassette deck so that access to cassette loading and tape controls could be accessed from the front.  This was implemented with a slide out drawer containing all of those controls.

While I had replaced the drawer pulley belt on this Beocord it was opening and closing sluggishly.
It should just open right up very smoothly and close shut in the same smooth manner.

The pulley motor, belt and pulley were all fine. The sluggish operation was elsewhere.

Checking the cassette drawer assembly I discovered that the source of the problem was in the drawer slide mechanics.  Manually operating the drawer slide I could feel that it wasn't as smooth as it should be.  A little too much friction for the drive motor.

Taking apart the drawer slide mechanism I discovered that it works using four rubber/plastic wheels.

I cleaned the rubber wheels and the metal posts they fit on really well.
Then I coated the metal posts with dry lubricant and reassembled the rail assemblies.
The drawer mechanism works beautifully now.  The motor and pulley mechanism effortlessly open and close the cassette drawer.

I also cleaned the cassette assembly.
The tape heads and metal capstan were cleaned with alcohol.
The rubber wheels were cleaned with CaiKleen rubber treatment.
I applied some Molykote DX white grease to the two roller bearings and tape head slide assembly components.

Here is the Beocord 5000 cassette assembly put back together.

The last bench test I performed was a cassette speed drift test and a WOW & Flutter test.
If this cassette deck had exhibited a lot of problems and had it required installing new cassette assembly replacement parts then more service manual adjustments would be required.

As this unit is in excellent shape I am only running a basic speed drift, WOW and Flutter test.

I don't have any B&O produced test tapes from when the Beocord 5000 was produced but I do have some newly created tape calibration cassettes from Genn Lab.

The tape I am using here is for running a DIN 3.15kHz speed test for a cassette tape speed of 1 7/8 inches per second.

I am currently using a Leader LFM-39A WOW & Flutter Meter.  It includes a Drift meter for checking the cassette speed.

With the LFM-39A meter Drift meter zeroed out I can play the Genn Lab test tape and make any necessary adjustments to the Beocord 5000 cassette drive motor.

This photo shows the cassette motor adjustment trimmer access point.

I selected the DIN Indication on the LFM-39A meter to match the test tape I tested with.

The Beocord 5000 did require a bit of tweaking on the trimmer and I set it as close to zero on the Drift meter as I could.

With the speed adjusted I checked the WOW & Flutter meter for the DIN 3.15kHz test tape.  I selected a range of 0.3 for the meter scale and WOW & Flutter for the test mode (W&F).  The output for the test was the right channel playback signal of the Beocord 5000. 

I can't claim this is equal to the B&O measurement methods used to publish the technical specifications for the Beocord 5000 but my results exceed the rated values.  While I am using a non-B&O test tape and WOW & Flutter meter, both are excellent test tools and I use them for all of the cassette decks I work on.

The Drift meter shows a value very near 0%.  The service manual says the value should be ±1.5%.  So very good there on tape speed.

The WOW & Flutter meter shows about 0.05% (remember that it is set for the 0.3 scale).
The service manual says that value should be less than ±0.13% so this Beocord is well within that range.

All that is left to do on this Beocord unit is to test making some recordings.  I have Metal and Chrome bias type tapes that the service manual calls for - TDK-MA and TDK-SA.
I can generate some test tone signals on the record inputs then see what the playback looks like on the audio analyzer.

Beogram 4002 Type 5513: Going over the chassis and mechanical parts

The two circuit boards that require recapping and other restoration work are done. Now it is time to dive into the Beogram 4002 cabinet and look in more detail at the electro-mechanical parts.

I like to remove the floating chassis to work on it. I plan on taking a lot of the tangential arm assembly apart anyway so removing the floating chassis makes that work easier for me.

As it turns out it also reveals some hidden problems.

I originally thought the three chassis lock down bushings were still good. They appeared to be intact but opening up the lock down mechanism proved otherwise.

First sign that the bushings were not in as good shape as I thought.

The more I handled the old bushings the more they fell apart.

Fortunately Beolover makes a set of replacement bushings so I quickly ordered a set from him.

Next up, a look at the condition of the tangential arm drive assembly.
I opened up the ball socket that houses the nylon nut the drive spindle rotates in to move the tangential arm assembly forward and back.

The old grease had started to harden up on this Beogram. The service manual says it should be an oily consistency. I will clean all of that off and reapply a new coat of lubricant.

Here are the tangential drive components removed and cleaned up.

When I reassemble the drive components I will also replace the original plastic pulley with a new, aluminum one I got from Beolover.

The above photo also shows that I had replaced the arm position sensor lamp with a new LED light source.

Here is the original LED.  They typically go out by now so I removed it and tested it. The LED was indeed dead.

I used an amber colored LED to replace it.

I will fine tune the lamp position as related to the angle its light hits the arm position sensor. There is a service manual adjustment for the expected sensor voltage when the lamp source is on.

I removed the original lamp source for the tangential tracking sensor as I will be replacing that light source with Beolover's LED replacement module.

With the light source module removed I can see that the metal tracking sensor shutter (that is attached to the tonearm base) looks like it is positioned correctly.

It mustn't rub on the black plastic housing of the tracking sensor but should be close to it. The service manual calls for a 1 mm gap.

The rest of the components that make up the tangential arm assembly are clean and move freely. I can see a few places where service manual adjustments will have to be performed but the arm lift and lowering  mechanisms move easily.

Other than a couple drops of synthetic oil on pivot points I don't see anything else that needs to be taken apart on the arm assembly.

I lubricated the tangential arm drive spindle with a new mixture of Rocol 1000 and Mobile NUTO H32 as called out in the service manual. There are other options if you don't have access to those products. I have collected some though so I like using what B&O originally used.

For the two shaft tie-rods that the tangential arm assembly rides on I applied a thin coat of white, DX Molykote paste.

The floating chassis is reassembled.  I just need to install the Beolover replacement bushings for the chassis locks then put everything back together in the Beogram cabinet base.

Beogram 4004 Type 5526: Tonearm Lowering Damping

The tonearm lowering on the Beogram 400x turntables is accomplished by a solenoid that engages/disengages per an electrical control signal. When the solenoid engages, the tonearm is free to lower. To prevent a straight drop of the stylus onto the record there is a damping piston that slowly lowers the tonearm.

On these Beogram 400x turntable restorations we always service the arm lowering mechanics to make sure it is operating correctly and continues to operate correctly.

This picture shows the arm lowering components before I worked on them.

There are just four screws to remove and two springs to detach in order for the arm lowering damper to be removed for service.

There you have it. The Beogram 4004 arm lowering mechanics removed for servicing.

The damping piston valve control is opened up (I remove it) and the piston pulled out of the tube.

Everything is wiped down then lubricated again before re-assembly.

Here are the lowering components re-installed. Pulling on the solenoid engage lever manually allows me to check the piston control valve and adjust it so the tonearm lowers to play position in about one second.

While the tangential arm components are removed from the chassis I will do more cleaning and lubricating. I will also change out the stationary arm lamp and sensor with the custom Beolover replacement part.

Before I get to that though, I was not completely happy with the installation of the optional phono grounding switch on the output board. A nice thing about having pictures to document a restoration is that I can review them and evaluate the results of my work.

On this Beogram 4004 output board I felt the need to use hot glue to secure the optional grounding switch. Without something to secure it the switch was wobbly. The 1M ohm trimmer resistor on the board takes up too much space to allow me room to install the switch the way I would like.

You can see the glue doing its job in the above pictures. Not horrible but I don't like the look.
I decided to go back and rework this installation. I changed out the 1M ohm trimmer resistor with one that has a smaller footprint (setting the resistance value to what the original setting was).

The new trimmer resister gave me enough space to install the switch better so that I don't need any hot glue. As you can see below the black hot glue peeled right off and is gone now. I like this version of the installation much better.

Beogram 8000: Replacing the Platter Tach Disc and Cleaning the Tangential Arm Assembly

Tonight I completed the tangential arm assembly cleaning and lubrication as well as changing the platter tach disc to a new, metal replacement.

The Beogram 8000 turntables started out with a plastic tach disc containing transparent and black markings that a photo-sensor uses to send pulses to the Beogram microcomputer. The microcomputer dials in the 33 1/3 RPM and 45 RPM speeds with these pulse signals.

Unfortunately, over time these plastic discs did not hold up so Bang & Olufsen replaced them with metal discs. As I mentioned at the beginning of this project, it is quite surprising that this Beogram 8000 actually has an original, functioning tach disc. Feeling that it is on borrowed time we decided to go ahead and give it a more permanent tach disc that Martin Olsen supplies. 

Here is the Beogram 8000 center hub with the tach disc next to the replacement disc I got from Martin Olsen.

...and here is the replacement installed.

Before testing the new tach disc I took the opportunity to clean the floating chassis and take care of some maintenance on the tangential arm assembly. I always clean off old oil and grease from the tangential arm drive so I can inspect the parts and apply fresh lubricants.

I was surprised to discover this Beogram's tangential arm drive screw bushing has a badly worn edge. It appears to come from the stress of the arm return travel.

This picture shows the worn bushing and the floating chassis before cleaning.

Here is a better look at the worn bushing after cleaning the parts.

For now I decided to turn the bushing around. That gives two solid edges pressing against the black, plastic transport bracket during the return travel of the tonearm. The stop travel puts the most stress on the bushing. During play the forward travel is in very small increments so there is very little stress on the bushing.

I reassembled the tangential arm assembly to give the new tach disc a test run. 

The Beogram speed testing with the new tach disc went great. The two speeds immediately lock in. I did some quick tests of the tonearm navigation and so far it runs very smoothly. Later, when I get to the record tracking tests I will re-evaluate how solid the tangential arm drive is working.

Next up I will re-install these components back in the main Beogram chassis and start on the mechanical service manual checks. It is getting close to actually playing some vinyl on this baby.

Beogram 8002: Service Manual Adjustments

Going in to the Beogram 8002 service manual adjustments I already know that the fixed arm and tonearm horizontal parallelism needs adjusting. The tonearm appears higher than the fixed arm as you can see in this picture.

The tops of the two arms should be the same height and that height should be 19.5mm from the top of the Beogram platter. So the fixed arm needs to be adjusted up and the tonearm needs to be adjusted down.

To make all of the necessary adjustments I have to get to the underside of the tonearm carriage assembly. That means removing the rails and the tangential drive screw. I have to do this anyway to clean and re-apply some lubrication.

The red arrow in this picture shows the adjustment screw for the tops of the arms (the horizontal parallelism adjustment). The green arrow is for the vertical parallelism adjustment (the gap between the two arms). I am pointing that out as it turned out I needed to adjust it as well.

After adjusting the horizontal parallelism I got both arms to the 19.5mm height from the platter surface.

I installed a new tangential arm drive belt.

I also cleaned and checked the lubrication of the platter hub. The following pictures show the Beogram from platter hub removed to the sub-platter re-installed. I was able to find a spare tonearm assembly cover trim piece. The original one was missing from this turntable and the wires were exposed.

When I put the top platter back on and connected the main board the tonearm and platter worked okay but I noticed something was not right with the tonearm. When the Beogram 8002 tonearm is at rest you should be able to push the arm towards the fixed arm and have it spring right back to centered position when you let go. With this tonearm I was detecting an obstruction that was hindering the spring back action.

I was concerned at first because I couldn't see anything wrong. The vertical parallelism looked correct. I took a peek into the tangential arm tracking sensor assembly.

Note the spring clip in the picture below. That spring mechanism moves the tonearm back to a centered position when you move the tonearm away from the fixed arm.

Everything was fine in there. Nothing was scraping.

I finally realized the tonearm vertical parallelism adjustment screw was the problem. It had been adjusted incorrectly. While the gap between the fixed arm and tonearm looked fine, the tonearm raise/lowering bar was not operating correctly in the V-shaped channel of the brass adjustment screw.

The following picture of one of my own Beogram 8002 turntables shows the tonearm lift/lowering bar and the V-Channel adjustment screw. The lift bar has a spring mechanism that will attempt to keep the bar pressed down on the V-channel when the arm is in the raised position (not playing). If you manually move the tonearm towards the fixed arm the lift bar rides up one side of the V-channel. When you let go the tonearm should pivot back to a centered position as the spring loaded lift bar returns to the bottom of the V-channel.

On this Beogram 8002 project turntable the lift bar was getting slightly stuck at the top of the V-channel screw when the tonearm was moved towards the fixed arm. By re-adjusting the V-channel screw (which is the vertical parallelism adjustment screw) I was able to get the tonearm back to its normal, springy self.

The tonearm and fixed arms are also vertically parallel to each other.

I test played one complete side of a record and observed the linear tracking working correctly as the stylus remained always centered. I could see the tangential arm assembly motor adjusting the tonearm position pretty much ever half turn of the record. Very nice results after all of that disassembly/reassembly of the Beogram mechanics.

The last check I wanted to make was the voltage level of the light driven sensor in the control panel. This is for the Beogram forward/fast forward and reverse/fast reverse function. After the Beogram has been operating for at least five minutes the voltage of the forward/reverse sensor should be around 620mVDC in its normal state. This check is done my monitoring control panel connector P5-4 to P5-3 (ground) and P5-6 to P5-3 (ground). To adjust the sensor voltage levels there are two screws on the control panel that operate an aperture for the sensor lamp source as seen in the picture below.

The procedure requires checking the voltages at both test points a few times as each screw is adjusted. Each adjustment screw can affect the measurement at both test points. After a few iterations I got the sensor to a satisfactory level.

Tomorrow I will re-assembly the Beogram 8002 (except for the dust cover lids) and do some actual record playing testing.