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 4002 (5513): Full Functional Restoration and a Test Spin with Volker Kriegel

This post describes the restoration work carried out on a Beogram 4002 (Type 5513) sent by a customer in California. My initial assessment of this unit is posted here.

This shows the unit with the platter and aluminum panels removed:

As usual, I started with the DC platter motor since it can take a few days until the oil infusion of the motor bearings is complete. This shows the motor extracted from the enclosure:

I disassembled to get the bearings out:

The bearings are the two small donuts on the black pad. I immersed them in synthetic oil and put the jar into my new vacuum chamber. I pulled a vacuum, and immediately bubbles came from the bearings foaming up the oil on the surface:

While this process was ongoing, I focused on the remaining restoration tasks. First came the disassembly of the arm lowering and carriage translation systems. This shows the setup in original condition:

When I started to disassemble the arm lowering mechanism I realized that the solenoid plunger actuator arm was only loosely screwed into the plunger. This pointed to earlier trouble with the solenoid having inspired someone to work on it. I extracted it and removed the plunger and arm:

I tested the plunger for magnetic polarization and indeed it was magnetic (an easy test is to put a small iron set screw on a flat surface and see if one can move it with the plunger - if it moves, the plunger needs to be demagnetized). A magnetized plunger can result in delayed solenoid release, which can cause the needle to drag across the platter during the return at the end of a record.

This shows my head demagnetizer together with the plunger.

Once the plunger was non-magnetic again, I reassembled the solenoid and put it back into its place. This shows the carriage after I removed all the moving parts. It is a good idea to place it on a soft pad to protect the fragile wiring on its bottom side:

This shows the extracted parts ready for cleaning:

And after an hour in my ultrasonic cleaner:

Nice and shiny! Before I reassembled everything I installed a new damper gasket:

This is good practice since the original ones are often hardened and out of shape, and that can cause inconsistencies in the arm lowering speed. It definitely can be a hair raising experience if the new $800 cartridge smashes onto the record without adequate damping...;-).

This unit also had a cracked spindle nut holder. They usually crack if the bolt is being tightened too much. Luckily there is a Beolover replacement part:

This shows it installed:

And here a view of the fully re-assembled carriage:

I also replaced the wobbly non-original carriage pulley with a precision machined Beolover pulley:

There is one more linkage on the carriage, which is often stuck preventing the arm from lowering. It connects the damper plunger end with the actual arm assembly. It is mounted on the sensor arm assembly. You can see it stick out from the V-cut that is in the small metal lever that is mounted to the back of the counterweight:

To get to the pivot point of this linkage the sensor arm needs to be removed. This shows the sensor arm laying flat with the linkage removed (watch out for the small spring that is under the circlip if you try this at home):

As usual it only took a light tug with my tweezers to liberate the small copper pad that aids the lateral movement of the tone arm when it is up:

I cleaned off the degraded double sided tape and glued the pad into place with a small dab of epoxy:

After the epoxy cured, it was time to re-install the sensor arm and do the lateral alignment of the arms. They should be perpendicular to the rods the carriage travels on:

Next I focused on the restoration of the circuit boards. It is best to replace the two power Darlingtons that are mounted on the solder side of the board first, while the board is still installed. This makes it easy to position them properly to match their mounting holes and solder pads. This shows IC1, which usually is a TIP120:

I replace these transistors with stronger types for prolonged longevity. The 120 can be replaced with a 102:

Please, note that these modern Darlingtons need a 100nF capacitor put across their outputs and GND in this circuit configuration. Without it a high-frequency oscillation can occur in the 21V power rail that usually throws off the record detection circuitry. The above picture shows this capacitor (yellow) soldered in between the emitter and a conveniently located GND pad.

This shows the other (pnp) Darlington TR8 (usually a TIP125, which drives the solenoid) replaced with a TIP107:

After replacing the two Darlingtons I removed the board to do the rest of the work. This shows the board as found in this Beogram:

My customer already had replaced the original Siemens RPM relay with a Beolover Siemens relay replacement:

Replacing this relay is a good idea, since it can be a source of RPM inconsistencies due to oxidation of the relay terminals. I went on and replaced all electrolytic capacitors, power transistors, RPM trimmers and the sensor amplifier TR3. I also replaced the biasing resistor of TR3 with a 25-turn trimmer, which is necessary to allow precise adjustment of the gain of TR3 to meet the 4V spec at its collector. Both transistor and trimmer are available via the Beolover store.  This shows the refurbished board: 

And a detail shot of the 'RPM section' with the added 25-turn trimmers for adjusting 33 and 45 RPMs:

Next I extracted the output board. It is located under the keypad. It carries the output relay and the delay circuit that ensures the channels only open up after the needle is in the groove. This shows the original condition of this board:

And after replacing the output relay with a Beolover replacement. I also replaced the electrolytic capacitor in the delay circuitry:

I also installed a switch (red) that allows connecting signal and system grounds in case there is a hum in the output.

After restoring the two boards, I focused on replacing the four incandescent light bulbs installed in Type 5513 Beograms. Two of them are in the RPM panel that is mounted above the keypad. I extracted it and flipped it around:

I noticed that someone had previously tried to open this panel up since one of the tab washers was loose:

They are single use, i.e. if they are pried loose they cannot be re-installed and a new one needs to be installed. In absence of a new one, I secured it in place with a 3mm retaining ring:

On to replacing the bulbs. This shows the bulb compartment covers pried off:

The small green boards are the Beolover RPM Panel LED Backlights that replace the bulbs.

I removed the bulbs and soldered the two LED boards in:

These little boards directly solder to the pads that connected the bulb wires. They can be considered an extension of the board that powers the bulbs:

The third bulb is located in the tracking sensor. This shows the original black bulb housing still installed:

I removed it which revealed the aperture that allows the sensor to measure the lateral deflection of the arm:

This shows the original bulb assembly in direct comparison with the Beolover tracking sensor LED light source:

The small with LED is mounted approximately in the location of the bulb filament. This shows the LED part installed:

The final, fourth, bulb is located in the small compartment at the end of the sensor arm. This shows the bulb (a non-standard replacement had been installed previously) together with the Beolover Sensor Arm LED Light Source and its alignment fixture:

I removed the bulb and installed the LED board:

This concluded the bulb replacements.

Time to focus on replacing the completely degraded transport lock bushings! (a frequent issue with this vintage Beogram 4002). But first I removed the original reservoir capacitor, which in this particular Beogram was a dual capacitance type: 

The earlier Beogram 4002 (Type 5513) featured a separate power supply for CD-4 pre-amplifiers that could be installed by replacing the standard output board. This separate power supply needed a 1000uF reservoir capacitance as well as a rectifier, which is bolted to the mounting screw of the capacitor can, hence the somewhat complex wiring around this capacitor.

After removing it, I started dissembling the transport locks to be able to remove the floating chassis. This shows one of the locks after removing the top plate. Some remnants of the original lock bushing can be seen:

This shows another of the locks. A beautiful example of degraded lock bushings!...;-):

This shows the enclosure after removing all components:

I vacuumed all the bushing fragments out, which is an important step since these fragments tend to get lodged under the chassis preventing its free floating, which is bad for vibration damping.

After the enclosure was cleaned up I installed new Beolover transport lock bushings. They come in two parts,

Which makes installation a snap. Simply insert one half from the bottom:

and the other half from the top:

Then the lock can be reassembled:

After the floating chassis was in place again I installed a new Beolover main reservoir capacitor assembly:

This Beolover part can be used for both single and dual capacitance reservoir capacitor setups. It replaces both, capacitor can as well as the little rectifier:

After bolting the PCBs and the keypad back in it was time to adjust the boas of TR3 to get the specced 4V at its collector:

Once the trimmer has been adjusted it needs to be moved 'below deck' to the other components:

Then it was time to measure the sensor response. The signal amplitude should exceed ~5.5V with the empty platter spinning under the sensor. This setup passed the test with flying colors as I measured a ~8V amplitude:

Each of the dips corresponds to a black platter rib passing under the sensor.

Now it was time to do the main mechanical adjustments of platter height, parallelism and floating chassis. When I put the platter needle shaft into the bearing I noticed that the bearing was loose and completely dunked up with a green matter, presumably some grease (shudder!...;-):

I cleaned the gunk off the needle and cleaned the stationary part of the bearing in my ultrasonic:

This allowed me to spin the platter again properly and I was able to complete the adjustments. After everything was aligned properly it was time to do the tonearm adjustments. First I adjusted the arm lowering limit:

This is an important adjustment since it is the fail-safe in case a circuit fault leads to lowering the needle onto an empty spinning platter. The limit needs to be adjusted that the tip misses the lower parts of the platter ribs by about 1 mm. The lower sections are located where the 7,10 and 12" set down points are. 

Before calibrating the tracking weight I replaced the flimsy circlip that holds the counterweight in place

with a M3 square nut and a washer:

With this nut the calibration can be locked in place, which allows shipping a Beogram without needing to recalibrate after arrival.

Then I calibrated the weight using a digital scale:

I usually adjust the counterweight in a way that the small weight dial is correct around 1.2g, which is the weight most B&O cartridges need. The dial is notoriously imprecise across its entire range. In general it is best to ignore the scale and simply adjust the weight occasionally with a scale to make sure is set properly. Digital scales are cheap and precise these days and can be found on amazon.

In the meantime the motor bearings had completed their infusion (no more air bubbles emerging from the bearings). I extracted the bearings from the vacuum chamber:

then I reassembled the motor and installed it in the Beogram. Then it was time for a 24 hrs RPM stability test with the BeoloverRPM device. In its 'slow' operation mode it allows precise measurement of the platter RPM as well as logging the speed in 10s intervals, which is perfect for measuring the RPM for longer periods of time to detect RPM inconsistencies:

This is the curve that I measured after 24 hrs:

This is pretty much as good as it gets with DC platter motors. With these motors there is always some long-term drift, usually caused by thermal effects, especially now in winter when I need to run the heater in my workshop during the day. At night it gets pretty cold in here and so there is a pretty big temperature differential during 24 hrs. In general, such drift is a normal characteristic of analog control systems. Overall, this change is happening very slowly on the timescale, and it is on a magnitude that is impossible for humans to discern.

The BeoloverRPM device has a second operational mode, 'fast'. In the fast mode it displays the measured RPM each time a platter rib passes under the sensor as a graph:

This is the curve I measured:

This graph covers about 60 platter rotations, or about 120 sec. of runtime. The interesting pattern is a convolution of real RPM changes and a measurement artifact that is a result of the very slightly irregular spacing of the platter ribs around the platter. On closer inspection, the zig-zag pattern is repeated every 24 measurement points (there are 24 ribs...) and can be regarded as a 'fingerprint' of a particular platter. It turns out that each Beogram platter has a distinct pattern due to manufacturing tolerances when the slots were machined for the black rubber ribs.

The overlaid sine-wavy pattern, however, reflects real RPM changes that are introduced by the feedback based control system that keeps the motor RPM constant. An evaluation of this wave pattern yields a wow and flutter percentage of about 0.1%. The service manual lists 0.05% as the spec for the DC platter motors, but this 2x difference may well be related to the different way this was measured in the 1970s in absence of modern microcontrollers. At any rate this difference is pretty academic since it is much to small to be discernible. This original DC platter motor is back in business!

After these measurements I was pretty close to a first test spin of this Beogram, and so it was time to replace the original corroded DIN5 plug

with a nice new all metal plug that has gold plated pins:

Beolovely!

I set the unit up for play and I selected a record I bought while I was in Germany this summer: "Topical Harvest" by Volker Kriegel, one of my favorite jazz musicians! This beautiful vinyl was recorded in December 1975 and issued on MPS Records. I have a re-issue (DC 228 274) from a moment when MPS was owned by BASF which at the time probably saw vinyl records as a great application for some of their polyvinyl chloride (PVC) output...;-). I bought this record at the RIMPO record store in Tübingen, a nice university town not far from Stuttgart. This store opened in 1975, i.e. the record may well have been bought there when it was new! This record is in excellent condition and after cleaning it with a CleanerVinyl ProXL setup it sounds like new! Almost no clicks and pops and a very quiet black space.

This picture shows the record playing on this great looking restored Beogram 4002! A perfect match:

My customer decided to get his Beogram updated and trade in his original motor for a Beolover SyncDrive. The SyncDrive has a much better RPM stability since it is based on a synchronously driven brushless motor that is controlled by a modern microcontroller. His unit will also receive a Beolover Commander remote control system for Beo4 remotes. This will allow embedding this Beogram into a Beo4 controlled B&O setup. 

I will also install a new aluminum trim on the new reproduction hood this Beogram came with.

Stay tuned for an update on this restoration!