Beogram 4002 (5513): Another Beogram From Houston - Electrical Work

Continuing the Houston Beogram 4002 restoration with the electrical work, here is the reworked main PCB.

Before

After

Some details to point out are the replacement of the speed select relay and the trimmers for the platter speeds (33.33 and 45).

The old trimmers for the platter speed adjustment have trimmer adjustment slots on the top and bottom.
The Beogram 4002 main board mounts where its trace side faces up so the speed adjustment is made from the underside of the board.  That is why the new trimmers are mounted upside down...so their adjustment screw can be accessed from the trace side of the board.

Here is the trace side of the main board.  You can see the speed trimmer adjustment screws.

Next are the replacements of the Beogram 4002 main board Darlington transistors IC1 and IC4.
Other Beolover Blog posts show the replacement of these two transistors with new transistors as a precaution against the aging Darlington transistors the Beogram 4002 uses for its power supply (IC1 21V) and the solenoid actuation (IC4 30V).

Another possible transistor replacement is 1TR3.  It is in the arm detector circuit the Beogram 4002 uses to determine if a record is on the platter or not. On the Beolover Blog restorations of Beogram 4002 (and 4004) turntables we check the 1TR3 transistor Hfe value to make sure it is good (typically, above 500).  If it is not, we change the transistor.  

Regardless whether 1TR3 is replaced and whether the lamp in the Fixed Arm (Detector Arm) is replaced, we do change resistor 1R26 from a fixed value (1Mohm) to a trimmer (usually a 2Mohm or 5Mohm trimmer).

This photo shows a 5Mohm trimmer for 1R26 installed on the trace side of PCB1.

The new trimmer will remain there for a while until I finish the rest of the electrical restoration work and am ready to test the Beogram.

The Beogram output board is next.
Here is the before photo of the output board.

Here is the after photo.

The only changed components on the output board are the Beolover replacement muting relay, a new electrolytic capacitor for C1 and the addition of a toggle switch to select whether the Beogram chassis ground is connected to the signal ground.  We have found that different grounding conditions can exist with various preamplifiers that result in ground loops.  Those cause hum in the phono signal and is noticeable during record play.  The grounding switch provides another option to handle that scenario.

Next, I replaced the incandescent lamps for the platter speed indicator panel.

Here is a little bit closer look at the original lamps...

...and the Beolover replacement lamps.  

The incandescent lamp in the Fixed Arm for the Detector Arm circuit was also replaced with a Beolover replacement LED assembly.

I changed out the Beogram 4002 control button panel with a refinished one.  The old panel was in bad shape.

The button panel contacts were oxidized pretty good so I cleaned them up to a nice shiny finish again.

Here is the button panel and contacts reassembled.

As I started installing the floating chassis components back into the Beogram 4002 cabinet, I replaced the original reservoir capacitor with a new Beolover capacitor assembly.  This new Beolover replacement component is very easy to install.

I also replaced the original DC Platter Motor with one that Beolover had refurbished for me.

Now I could install the circuit boards back into the Beogram 4002 cabinet and make some electrical adjustments.

With the electronic components re-installed in the Beogram cabinet it was time to tackle the adjustment of the Detector Arm Circuit.  The new 1R26, 5Mohm trimmer needed adjustment so the DC voltage measured at the 1TR3 collector is 4 VDC.

With the steady state voltage adjusted on 1TR3 the new 1R26 trimmer can be moved to its final position on the component side of PCB1.

Another PCB1 adjustment is with trimmer 1R88.  This trimmer adjusts the voltage at the collector of 4IC1 which is the sensor for tangential arm position. That is the sensor that receives the infrared light from 4D1 as the position slide moves between light and sensor during arm movement.  The light, sensor and position slide detect the arm set down points for various size records as well as the run-out groove detection.

The 4IC1 collection should be set to 5 VDC when the clear portion of the position slide is between the sensor and lamp.

So far all of the adjustments and measurements have worked out as called for in the service manual.

I continued on with the calibration of the tone arm groove tracking.
For this adjustment I like to make a crude adjustment with the bracket connected to the base of the tonearm which holds the aperture slot controlling light to the tracking sensor.

Note that I also make this crude adjustment with the eccentric tracking adjustment screw in its center position.  That is so I have room to make the fine adjustment in either direction.

I adjust that bracket so the arm can be lowered and it just stays put (it doesn't try to move forward on its own).

After that is achieved I loosen the set screw for the eccentric (fine) adjustment screw.

A test record can now be placed on the platter (without a platter belt).
The tonearm is advanced to a center track on the test record and lowered.

The arm should not try to advance.

Manually rotating the platter with the test record should result in the Beogram servo motor turning to advance the arm within one revolution of the platter.  It should advance the arm every platter revolution after that.

The eccentric adjustment screw is used to dial in that calibration.  
Extra fine adjustment can be made with the small trimmer on top of the Beolover tracking sensor lamp assembly.  Those adjustments increase or decrease the intensity of the LED used as the sensor light source.

This photo shows an adjustment with the eccentric screw.

Using an oscilloscope I measured the empty platter signal at the 1TR3 collector to check the health of the sensor output.

Two last measurements before actual record play are to re-install the platter belt and adjust the 33.33 RPM and 45 RPM platter speeds.

For these adjustments I use the Beolover RPM Tool as the measurement instrument and the two speed trimmers on the main, PCB1 board.

The owner of this Beogram 4002 also would like the Beolover Remote Commander installed as part of the restoration.

My next steps will be to first, finish reassembling the Beogram 4002, then some quick test play of some vinyl records.  

After that I will install the Beolover Remote Commander and resume testing record play on this Beogram (the real fun part).

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.