Beogram 8000: Tonearm Lowering & Raising Components

In my recent Beogram 8000 project I had to investigate the tonearm lowering and raising functionality. I have also had to look at the part of the Beogram 8000 on one of my own units (where the lowering was sticking, then suddenly dropping). I thought is would be useful to post some details of the Beogram 8000 components involved with the tonearm lowering and raising control.

First are a couple of pictures of the tonearm in the raised position to get familiar with some of the key players.

There is a solenoid involved that is controlled by the Beogram microcomputer and an op-amp circuit that generates a ramp signal to lower and lift the arm via a lever and control bar.

The above pictures show the control bar pressing down on a tonearm linkage component. There is a slot in the exposed end of the linkage to adjust the (vertical) parallelism of the tonearm. Adjusting the linkage position affects the gap between the tonearm and fixed arm.

When the control bar is pressed down on the linkage the tonearm is at its fully raised position. There is a metal spring mechanism that the normal position is designed to keep the arm raised. The solenoid plunger moves a lever that presses against the spring to raise the control bar (and allow the tonearm to lower).

The next picture shows the Beogram with the tonearm in the lowered position.

This picture was taken with the Beogram actually playing a record. You can see the control bar was pushed away (by the solenoid) to allow the tonearm linkage free movement. When the control bar is raising it does so with a controlled motion so the arm slowly lowers to the vinyl record. When the stylus touches the groove the tonearm obviously reaches the limit of its drop. The control bar continues to raise a bit more so it is no longer in contact with the linkage.

At this point the tonearm movement is controlled by the record groove and the Beogram tangential tracking detection.

Here are a couple pictures of the arm lowering/raising components on a stripped down Beogram 8000. The tonearm is removed in these photos. Only the pivoting base remains. These pictures give a good view of the control bar. You can see that the bar travel is managed by a guide slot in a metal bracket.

WARNING: Removal of the tonearm is not part of any adjustment procedure of the Beogram 8000. Attempting to remove the tonearm can cause serious damage and render your Beogram unusable. This is because of the delicate phono wires that travel through the arm and pivot base. These pictures were available for me to make because the Beogram pictured was a damaged unit where the tonearm wires were severed.

Here is a photo from the back of the Beogram with tonearm installed showing another angle of the control bar.

One more photo of the control bar and related components from underneath the tangential arm assembly.

The above photo also shows the location of the adjustment screw for the other tonearm parallelism (horizontal) adjustment. This is for aligning the top surface of the tonearm with the fixed arm when the tonearm is in the raised position.

Now for a look at the electronic part of the arm lowering and raising. Here is the relative circuit as taken from the service manual schematics. The phono cartridge muting circuit is also shown as both the muting and arm lowering/raising are controlled by the same signal from the Beogram microcomputer.



The part of the circuit shown as my test point (TP) for the lowering/lift integrator signal is the drive signal for the solenoid. When the arm is being lowered that signal is a slow ramp signal from 0V up to around 12.6V. When the arm is being raised it is a fast signal from about 12.6V down to 0V.

Here is a view of the arm lowering and raising signals at the test point relative to the microcomputer control signal.

So far in my encounters with these Beogram 8000 turntables, any issues with the tonearm lowering and raising have been mechanical problems. Something interfering with the mechanical movement of the arm lowering/raising components.

If you are having problems with this area I recommend putting the Beogram in service position and studying the movement of the control bar in relation to the arm linkage as well as the movement of the solenoid.

I observed on one of my troubled turntables the solenoid and control bar operating correctly but the arm linkage was sticking, then dropping all at once. I took apart most of the involved components and made sure everything was clean and nothing was interfering with the movement. Once re-assembled the arm lowering worked perfectly again.

If there is a problem where the solenoid isn't working, here are some pictures of the Beogram 8000 solenoid components disassembled. I mention again that I haven't encountered a failed solenoid yet and these pictures were taken from one of my spares just to have as a reference.

I hope the pictures are useful to you Beogram 8000 owners wanting to trouble-shoot any tonearm lowering problems.

Beogram 8000: FOD Bites Me In the ***

Having a little experience in the aircraft industry I know about the acronym FOD (Foreign Object Debris). This post is an example of why the term exists and how it can even apply to turntable restoration.

In my recent Beogram 8000 restoration I was extremely happy with the final results and shipped the turntable back to the owner. Although the packing was as good as it could be there was undoubtedly a lot of vibration during the truck journey. When the Beogram 8000 arrived back home the owner noticed the tonearm was drooping. That should never happen. After failed attempts to solve the problem by phone the Beogram had to be shipped back to the workbench.

As soon as it arrived back I unpacked up the Beogram 8000 and saw that the tonearm was still drooping down instead of level with the fixed arm.  I put the Beogram into service position and the tonearm popped back into its normal position. That always happens doesn't it?

The question is what could have been causing the problem?  I started examining every detail of the arm lowering and raising parts. It is natural to suspect the arm control solenoid and some electronic control but this Beogram had extensive bench testing without any such incident. I was pretty sure the problem was mechanical.

Here are some pictures of the Beogram 8000 arm lowering/raising parts.

I exercised the arm lowering and raising manually to see if I could feel any restriction but everything was nice and smooth operating. I also powered up the Beogram and operated the Play/Pause/Stop functions a number of times while observing the solenoid action. No problems there. I wondered if something in the tonearm linkage just slipped a little during shipping and now it is all okay.

One new thing I did notice about this Beogram was that the tangential arm carriage drive was noticeably louder going forward than returning to the parked position. Of course I remembered that this turntable had a broken tangential drive shaft bearing. I had reversed its position and it worked fine while it was here earlier. I didn't discern any difference in the tonearm scanning (noise) at that time. However that damaged plastic lip on the bearing must be the source of why one scan direction is now louder than the other.

So while I hadn't found the source of the tonearm drooping problem I felt I needed to go ahead and fix this tangential drive noise issue. I had one spare drive bearing remaining in my stock so I grabbed it and prepared the install. This operation means taking the tangential drive off its rails and flipping it over to get to the bearing. While there I can also examine the tonearm lowering and raising components from another angle.

This is where I discovered the prime suspect of the tonearm problem. A piece of FOD was visible near the arm control lever.

That piece looks familiar! I looked at the tangential drive bearing and sure enough, that is the piece that had broken off the bearing...probably years ago.

If that small piece of plastic had shifted into the slot that the tonearm lowering bar slides in it could easily have caused the problem where the arm would not fully raise. I can only surmise that is what happened but it seems highly likely. The Beogram hadn't and still doesn't exhibit any bad behavior with the arm functionality. I don't think it is a coincidence that this plastic piece was in the location I found it and it not be the prime suspect.

I installed the new, fully intact, spare drive bearing and the tangential arm scanning operations are smooth again.  They operate with only the expected, soft whirring of the motor.

Now for the important lesson (re)learned about FOD. Seeing that the original bearing had a broken piece off the lip I should have done a more thorough inspection of the Beogram to search for it. I had just assumed it was long gone. On the Beogram 400x turntables where their transport lock bushings are often deteriorated into a thousand pieces I have to do a full cleaning of every part. This incident shows that even one broken piece of plastic debris can cause problems.

I am an optimist though so I take the view that this was a good learning experience and this Beogram needed the drive bearing changed anyway so it worked out good. It is time for a quick play test then I will ship it back home again.

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: Reworking The Phono Muting Relay...Again

Since the replacement of the Beogram 8000 Control Panel board with a spare I had this Beogram has not had any mishaps with unscheduled pauses during record play.  During retesting of this however, the spare phono muting relay I installed is acting up like the original one did. The problem is intermittent but when it occurs the phono signal is not muted when the tonearm is lifted.

This still sounds like a relay problem and I didn't really like the fact that I had to use a replacement for it from another Beogram 8000 turntable instead of with a brand new relay. The problem is the Beogram 8000 output board is designed for a National type relay that is no longer available.

The Beogram 8002 output board it turns out is interchangeable with the Beogram 8000 and the Beogram 8002 muting relay is still available new from my favorite suppliers.

Before swapping output boards and relays I want to do diligence and measure the Beogram Lift signal.

The Beogram 8000 Muting and Lift circuits are related. A Lift command from the processor causes the tonearm to lower or lift followed by the muting circuit engaging or disengaging the phono muting relay.

I checked out the three test points shown on the diagram on my oscilloscope to see what is happening.

The above picture shows the Lift command in red from the Beogram processor. About 2.5 seconds after the Lift signal (to lower the tonearm), the muting relay engages to allow the phono signals to function.

When the tonearm is raised the Lift signal fires again and the muting relay disengages, shorting the outputs together.

I observed this switching function for a while and never saw any problem with it. However, I did see a problem with the muting relay. While the oscilloscope was measuring the Lift signals I connected my DMM to the phono left and right signals to measure the resistance.

Initially, before turning on the Beogram, the resistance measurement between the left and right channels was a short circuit. I measured about 0.4 ohms. When the tonearm lowers the phono signals are opened up and I measure an open circuit. When the tonearm is lifted the left and right channels should return to a short. There were a few times that I observed around 250 ohms to 280 ohms across the channels instead of a short. So the relay contacts are still the problem.

It was time to go ahead and use a Beogram 8002 output board in place of the original Beogram 8000 output board.

Here is the Beogram 8002 phono output board. The following pictures show changing out the muting relay with a new, sealed Omron relay. I also installed the ground switch option on this replacement output board assembly.

Now it was ready to swap the output boards.

The following picture shows the difference between the two output boards when the phono muting is on.

The new relay does a much better job and I feel much better having a brand new relay installed.

The other test point I wanted to measure is the Beogram 8000 tonearm lowering circuit. The damping of the tonearm when it is lowered to play a record is often a trouble spot. Sometimes owners observe the tonearm just dropping instead of slowing lowering. The control of the arm lowering is via an OpAmp circuit that is used to generate a ramp voltage to engage the tonearm lowering solenoid.

This Beogram has been lowering and raising exactly as it should so I captured some measurements to use as a reference. I measured the ramp signal as it reacts to the processor Lift command.

Whew! The Beogram 8000 is connected once again to my audio system where I will exercise it again before sending it home.