Beogram 4002 Type 5513: Going Through the Service Manual Checks and Adjustments

This weekend I started in on some of the Beogram 4002 service manual checks and adjustments.

There are both electrical things to do and mechanical.

Electrically I want to make sure photo sensors are generating good signals when they are activated by their light sources. The Beogram 4002 is an analog control system and it depends on correct voltages to work correctly.

Mechanically I will make sure the Beogram fixed arm and tonearm are aligned. I will need to set the platter height to the fixed arm (and tonearm) then set the lowering limit of the tonearm. The tonearm tracking force will have to be adjusted as well.

Finally there is kind of a duo electrical and mechanical adjustment, the tangential tracking sensor.
I will adjust that tracking per the service manual so the Beogram is properly advancing the tonearm (with phono cartridge) as it plays a record.

Those are a lot of tasks for sure and many of the mechanical adjustments affect each other. This process can sometimes be easy and other times take many repetitions.

My first adjustment was on the tangential drive spindle that moves the tangential arm assembly when playing a record. The tangential drive motor rotates the spindle which connects to a nylon nut on the tangential arm assembly (sled). That pushes the assembly forward and back.

The tangential drive spindle can be adjusted for vertical height from the floating chassis and for horizontal distance between the spindle and front tie-rod.

The next three pictures show checking the the vertical adjustment at different points on the spindle.

The horizontal position is similar. I used the calipers to check that the distance between the front tie-rod and spindle were the same at both ends of the spindle.

With the spindle driving the tangential arm assembly correctly I can check the arm position sensor to see if the voltage level of the sensor is correct.

Here is a photo of the arm position sensor and lamp again. The tangential arm assembly has an acrylic lens that passes between the lamp and sensor as the arm assembly moves across the platter.
Markings on the lens affect the sensor voltage which is used by the analog control system to determine what to do.

The arm position sensor is part of this circuit.

The service manual adjustment for this sensor is to move the Beogram tonearm to a position where the sensor lamp is hitting the sensor through a clear section of the position lens.

At that position the collector of the sensor (4IC1) should measure 5 VDC. If it does not, adjust trimmer 1R88 to get the 5 VDC. The result of that adjustment should also result in 0.7 VDC at the base of transistor 1TR17.

Since the original position sensor lamp (4D1) was burned out I had to replace it. The replacement LED is not the same as the original one so I expect to have to adjust 1R88.

Sure enough, the initial voltage at the sensor collector (4IC1) is only 1.5 VDC.

Using the trimmer on the main board (1R88) I was able to adjust the voltage for the 4IC1 collector.

With that adjustment out of the way I decided to take a preview look at the signal being produced by the fixed arm sensor.  Beolover has a great video about the arm sensor. How it works and what the proper sensor signals looks like.

On this Beogram 4002 project I connected an oscilloscope probe to the 1TR3 collector to measure the record detection signal.

The signal with no record on the platter looks like this.

The Beogram 4002 record detection circuit is working with that signal but we know that the signal level is lower than what the service manual calls for.  The peak should be closer to 6V and the dips in the signal should reach 0V.

That means I will return to this circuit and do the adjustment Beolover shows in the video.

The next part of the service manual adjustments I made were for the tonearm.
As I started playing with the Beogram tonearm movement (i.e. lowering, raising, pivoting) I noticed that when the tonearm lowered it would pull towards the fixed arm side. The tonearm did not lower straight down and raise straight up.

That pull usually means some parts that are supposed to move freely are rubbing together back at the tonearm pivot base. In addition, I noticed that the space between the fixed arm and tonearm was narrower than the 7.7mm gap specified in the service manual. So there were a couple of things out of alignment.

There are a number of adjustment screws to get the tonearm and fixed arm aligned. A problem is that they can affect each other so it often takes several iterations to get everything aligned to where they are per the service manual.

To address the distance between the two arms it took adjusting the fixed arm position and lowering/raising arm (the metal connecting arm between the tonearm and fixed arm).

Those adjustments addressed the parallelism between the two arms and put the gap at the prescribed 7.7mm.

During the adjustment of the lowering/raising arm I also adjusted the position of the tonearm counterweight. I found that it was set too close to the back of the tonearm and the side nearest the fixed arm was hitting the back of the fixed arm...causing the tonearm to lean towards the fixed arm when lowered. Adjusting that counterweight assembly fixed the arm lowering problem.

I need to calibrate the tracking force, arm lowering limit and stylus position but first I checked the height of the platter to the fixed arm (and tonearm).  The service manual calls for the distance from the metal platter surface to the top side of the fixed arm to be 23mm.

I have a measurement tool I keep set at 23 mm for that check. If the height is not correct the platter bearing must be lowered or raised as required. This Beogram only took a couple of iterations to get it set correctly.

Now for the tonearm lowering limit. The Beogram should be adjusted so the tonearm lowers at a maximum position where the phono cartridge stylus sits about 0.5mm above the lower rib section of the platter.

For the phono cartridge position on the platter and another parallelism check I use a piece of thread tied to the center spindle and run it to the right side of the Beogram. Then I check that the stylus sets down on the thread at the edge of the platter and at the spot where the end of a record will be.

The Beogram tonearm is now properly set up where I can complete the tracking force adjustment.
The tonearm counterweight is already pretty close from earlier when I adjusted it to allow proper pivoting of the tonearm.

Now I will measure the tracking force and set the tracking force knob to 1 gram.

All of the tonearm adjustments so far are predecessors for the Beogram 4002 record tracking adjustment.

For the tracking adjustment the tonearm will be set down at the center of a record album. The platter belt will be off so the turntable is not turning (by the motor).

The adjustment procedure is to manually rotate the platter (and record) so that the tangential arm motor (carriage motor) advances the arm assembly within one to two rotations of the record.  After that the motor should advance after every rotation.

Here are the adjustment components for the record tracking.

I typically set the eccentric screw for the aperture adjustment to the center position first. Then I adjust the diaphragm position so that the tangential arm is close to triggering the tracking sensor when is lowered. That way I know I am very close to where I need to set the aperture adjustment screw as well as knowing I have plenty of play in the screw to adjust with. Of course I also have the Beolover lamp intensity trimmer for any fine tuning later.

The Beogram is ready to connect up the platter motor again and check the two speeds (33¹⁄₃ RPM and 45 RPM). For the speed adjustments I will use the Beolover RPM measurement tool. This is the same tool he uses to test the platter motors after a rebuild of the motors. For people that work on or own a lot of Beogram tangential turntables it is a very nice test tool to have.

I am really pleased with this Beogram 4002 restoration so far.  I still have to go back and address a few things.  The record detection circuit needs calibrating so the detection circuit gets a full signal.
The two meters for the selected platter speed need to be replaced to the Beolover LED lamp modules. That will provide one more piece of stability in the motor...because the lamp is actually part of the speed control circuit. Once those lamps are changed I will recheck and readjust (if necessary) the platter speed trimmers.