Beogram 4004 for the Workshop: Measurements & Adjustments

After performing the restoration work on the two boards, PCB 1 and PCB 8 I moved to checking the voltages on 1TR3 collector for the record detection circuit and on 4IC1 collector for the position sensor.
The new 1R26 5MΩ trimmer will be used to set the voltage on the 1TR3 collector to 4 VDC.  The 1R88 trimmer will be used to set the voltage on the 4IC1 collector to 5 VDC (when the sensor is getting its light stimulus through a clear part of the position scale).

Here is the position sensor adjusted.

Here is the record detection circuit adjusted.

Trimmer 1R26 can now be desoldered and soldered in place on the other side of the PCB 1 board.

I will double-check the actual record detection waveform on an oscilloscope later but first...
I need to do some work on the tangential arm assembly.

This Beogram 4004 turntable is in really great condition but I did notice during the assessment checks that the platter motor and the tangential arm servo motor make a lot more noise that normal.

The platter motor being noisy isn't too surprising given that they often are lacking oil in their sintered bearings (self-lubricating bearings). That happens after 30 years.
Whenever I have sent Beolover some Beogram 400x platter motors for restoration I often send along a couple of my own.  That worked out nicely here as I have a nice Beogram 4002/4004 DC platter all nicely restored by Beolover to swap out with this noisy one. Note that this one is marked serial number 1947049. 

Of course the restored DC platter motor is super quiet.  There is still the tangential arm servo motor though.  It was making the most noise.  Especially when the arm was returning to the stop position.

I removed the servo motor from this Beogram and tested it with a bench power supply to see if the motor was still noisy when out of the Beogram chassis.  It definitely was.  Even at slow speed.
The servo motor is sealed and isn't a motor Beolover currently offers a rebuild for so I grabbed a spare servo motor and figured that would be a quick and easy swap.

It turned out not to be the case. The next three servo motors I tried were all too noisy for my liking.
I finally found a nice quiet one from a Beogram 4002 turntable.

Here is a photo of the four noisy servo motors.

Along with the good, quiet, replacement servo motor I installed a new aluminum tangential arm pulley for the Beogram 4004 spindle assembly.

Even though I didn't photograph the spindle cleaning and lubrication I took this opportunity to perform that task as well. I used the same lubricants as I used on my other Beogram 400x restorations.

A mixture of the NUTO H32 and Rocol MTS 2000 is used for the spindle lubrication.
I use the DX Paste Grease for the front tangential arm rail.

The next set of tasks were to get the Beogram 4004 tangential arm assembly checked and adjusted.
- First thing is to set the platter height where the surface of the top platter is 23mm below the top of the fixed arm assembly.
- Second thing is to set the lowering limit of the tonearm so the phono stylus is about 1mm above the lower platter rib section.

- Third is to calibrate the phono cartridge tracking force.

Platter height

Stylus lowering limit

Tracking Force Calibrated
I calibrate the tracking force at the 1 gram position as it is the most commonly used.

I use threadlocking Loctite for the adjustment screws so they can't move during any vibrations the turntable might experience (like transporting).

Now that the tangential arm components are adjusted to their correct positions I can set the tracking sensor sensitivity.

The position sensor, tracking sensor and record detector sensor lamps on this Beogram are all still functioning good so I decided to leave them as is for now. 

Remarkably the tracking sensor was already very close to a proper adjustment. It only required a small tweak of the eccentric adjustment screw to fine tune the setting.  

I reinstalled the platter on the Beogram and adjusted the two speeds using the Beolover RPM tool.

The platter motor silently and easily adjusted for the two speeds.

Now that the platter spins properly I checked the record detection sensor signal when no platter is present.

The record detection circuit is a good solid signal at 33.333 and 45 RPM platter speeds.  The low part of the signal goes all the way to zero volts which is what I am expecting.

Last on the task list for this post is to replace the platter speed indicator lamps with the Beolover LED lamp assemblies. It is always worth mentioning that these lamps are part of the Beogram platter speed control circuit and do affect that performance.  Beolover has measured an increased stability in the platter speed control with these LED assemblies over the original incandescent lamps.  The Beolover LED assembly is designed to work with the speed control circuit the same as the incandescent lamp but without changes due to lamps heating up.

Here is the Beogram 4004 speed indicator panel.

Here is a look at one of the Beolover Beogram 4002/4004 indicator lamp assemblies. 
They come as a set of two (left sided mount and right sided mount).

The LED lamp assemblies are soldered in place and some included double-sided tape helps secure the small boards to the panel.

The speed indicator board is complete and ready to reinstall.

This Beogram 4004 is ready to start playing some records.