Beogram 4004 Type 5526: Working the floating chassis components on the second Beogram 4004 from Texas

I find it easiest to work on the tangential arm assembly and other components that live on the Beogram floating chassis when everything is removed from the cabinet.

Earlier I spotted a couple of problems with the tangential drive motor position in its housing. I also noticed the usual hairline cracks in the drive pulley. So my first step was to remove those two components.

The vibration dampening material hasn't completed deteriorated in this Beogram but it has started. With most of it still intact this one won't be such a mess to clean up after.

In the first Texas Beogram 4004 project it was decided to leave the original tracking sensor in place. On this second Beogram 4004 restoration the owner wanted to go with the Beolover replacement tracking sensor lamp module. It isn't difficult to install and is even easier when the tangential drive motor and pulley are removed.

The first Beogram 4004 unit had a burned out carriage position sensor lamp. From the symptoms the owner described on this unit I suspected this one was out too. I removed the original LED lamp and tested it. Sure enough, it was dead.

Another difference in this second Beogram 4004 restoration is the fixed arm (platter) detector lamp will be replaced with the Beolover replacement part. I have done a few of these and while not extremely difficult the task requires patience, care and a steady soldering hand.

The fixed arm sensor assembly mount pulls out from the end of the fixed arm. Do not force it or use a tool to pry the black plastic housing out of the aluminum frame. Doing so could damage the arm or leave an unsightly scar.

Here is the sensor assembly pulled out of the arm.

Here is the new sensor lamp assembly soldered in place. I will leave the sensor assembly out of the fixed arm for now until I can test it for final positioning. The design of the new part will always get it close to where it needs to be but we always measure the signal and fine tune the position for the best signal.

Next up is the arm lowering damper assembly.
This Beogram is in good shape but some of the parts involved in the arm lowering and raising don't feel like they operate as smooth as I expect.
I removed several key parts for the arm lowering to inspect, clean and lubricate them.

The arm damping cylinder is another lubrication where I found the original lubricant called out in the service manual. You can use substitutes as shown in other Beogram 400x restorations on this site but I wanted to see what the original lubricants were like and was able to acquire some.

Continuing with the tangential arm lubrication I removed the spindle assembly for cleaning and re-lubricating. The first time I removed one of these Beogram spindles I thought it was really dirty from the years of use.

It turned out that is the color of the original oil/grease mixture the factory lubricated the Beogram spindle with (Rocol MTS 1000 plus Mobil Nuto H32 oil).
I cleaned the spindle parts and re-lubricated them as I did the first Beogram 4004.

Next I rewrapped the tangential drive motor with new vibration damping material (1/16" self adhesive neoprene material).

I also installed a new drive pulley (aluminum). The drive motor and pulley look centered and aligned now.

I finished the lubrication of the tangential drive assembly and now it is ready to go back into the Beogram 4004 cabinet.

Beogram 8000: Sensor Checks and Adjustments

The problem with the Beogram 8000 detector arm not detecting an empty platter turned out to be a simple adjustment to the sensor source lamp positioning.

The Beogram 8000 schematic shows the detector arm circuit and what the expected sensor signal should look like.

Measuring at C19 I could see the signal was not as strong as it needed to be.

I used a flashlight to apply more light and saw that the sensor output increased up to a working level.

The easiest thing to adjust and check at this point is the sensor source lamp position. I opened the lamp and sensor housing to move the lamp down a little inside the housing.

That did the trick. The detector arm now functions normally with the correct output voltage on the detector circuit.

While I had my Beogram test setup in place and my scope warmed up I checked the tangential arm position sensors. Here is the circuit diagram.

Both sensor outputs look good and the Beogram has been working as it should with regard to the tangential arm movement.

Another sensor output to check is the platter speed. This Beogram still has the original, plastic printed tacho disk. Let's see how it measures. Here is the circuit and measurement point.

Here is the sensor output for 33⅓ RPM and 45 RPM.

Last are the forward/reverse scanning LDR sensors. This is the adjustment I always add my custom connector for so I can check the LDR voltages at any time without having to completely open up the Beogram again.

Here is the circuit.

Here is a photo of the test connector I always add for the this LDR adjustment. This photo is from an earlier Beogram 8000 restoration project. It is the same on this current project. The wire colors used on the test connector were chosen to match the Beogram ribbon cable for those signals.

Here are the forward and reverse LDR measurements after adjusting them to be between 0.6 VDC and 0.7 VDC.

I believe this Beogram is working correctly electronically. Now I need to check the tonearm balance and the distance to platter surface. After that I will check the cartridge tracking and, if necessary, adjust the linear tracking sensor. I should be playing records on this Beogram real soon.