Beogram 4000: Installation of Newly Designed Beolover RIAA Pre-Amplifier Board

****Update: The Beolover Beogram 4000 internal RIAA pre-amp is now available at the Beolover Store*****

In the past I had a few inquiries for an internal RIAA pre-amplifier board for the Beogram 4000. So when the recent re-design of the Beolover RIAA pre-amplifier for DC motor Beogram 4002 and Beogram 4004 finally came together, I decided to adapt the circuit for the Beogram 4000. 

The owner of the Beogram 4000 that re-visited my bench last week for a little warranty issue decided to let me install the new board in his unit.

This post shows how I installed it. For measurement data, please, check out my post about the characterization of the 4002/4 version, which has the exact same circuit.

This show the board in its current form:

It is still a prototype board and has a couple features that will be removed for the final version. I was not sure how I would power the amplifier in the 4000 since it is set up differently compared to the later 4002/4. I ended up connecting to the 24V rail. The amplifier section of the board is not affected by this, and so this version is already suitable for regular use. 

The 4000 is still fully wired with directly soldered harnesses. This means the board needs to be soldered into place in the 4000. In the 4002/4 the board is simple plug and play due to their more modern design with wire-to-board connectors. Due to the 'permanent' soldered installation I gave this board two switches, with which one can route the output signal through the amplifier, or bypass it in case a traditional Phono amplifier input will be used.

Anyway, let's do the installation! Exciting!:

This shows the output terminal of the Beogram 4000 with the red switch that I installed last year to enable connecting signal and system grounds if there is a hum issue.

Here a detail-photo of the terminal:

The first step was to remove the output cable and the switch from the terminal:

Then I removed the screws that bolt the terminal to the enclosure bottom:

The Beolover RIAA board simply screws on top of the terminal 'bar'. The mounting holes are slots, i.e. the board can be pushed up to the wire terminals for directly soldering it to the contact pads on the board:

The next step is to solder the terminals to the matching board pads:

Then the output cable can be soldered to the output terminals of the RIAA board. They are spaced exactly like the terminal pads, i.e. the output wiring does not need to be modified, and it can directly be soldered in place:

The last step is to connect the red power wire to the 24 rail of the Beogram. A convenient spot is on the main board, where the 24V rail comes in on another red wire.

The strange 6-diode contraption in the back is the Beolover's approach to replacing the Wien oscillator light bulb with a diode based Automatic Gain Control for easy oscillator startup....but that is an entirely different story...;-)

The final step is to pull the output cable a bit further out of the enclosure in the back since the RIAA board pushes the wire terminals a few cm towards the back of the enclosure.

And that is it. This Beogram 4000 can now directly be connected to any modern receiver without Phono input.

Beogram 4000: Platter Motor Stopped Working

Last year I restored a Beogram 4000 from a customer in the UK. Unfortunately, he recently contact me since the platter motor stopped working. 

After receiving the unit I put it on the bench and started looking into the issue. first I checked the power rails and the reed relays. Everything tested fine. The next step was verifying the motor signal. I measured at the motor capacitor, and there indeed was no signal.

So I did the classic 'follow the signal' approach. I measured the oscillator signal at the collector of TR8, which checked out o.k.: 

The oscillation is not a perfect sine wave, since I had to replace the light bulb in the Wien oscillator with diodes when I restored it last year.  But so far so good...now I measured at the base of TR9, which should essentially show the same signal, just shifted to zero V since it is coupled via C6 to loose the DC component. But the signal was gone:

So it had to vanish somewhere between TR8 and TR9. I measured all the connections between TR8 and TR9, and it turned out that the signal vanished after the motor trimmer VR3. I replaced VR3 with a modern 5k 25 turn trimmer, but no cigar! The signal was still gone after the trimmer. At that point it dawned on me that there must be a short to GND somewhere. A closer inspection of the board yielded this:

R24 and R20 were touching! Something had bent the two resistors together, which effectively connected the base of TR9 to GND. I bent the resistors apart, and voila: The motor signal returned. This is the 33 RPM trace

and here is the 45 RPM.

So the trimmer had been replaced unnecessarily. This shows the new unit peeking through the access hole in the PCB for adjusting the motor voltage:

I put the platter on and a cartridge to see if I could play a record successfully. But the arm did not lower on the record. I realized that the sensor arm was dark, i.e. no power to the LED light source I had installed last year. I measured the voltage at the LED and it turned out that it was 0V. So I looked for interruptions in the connections between the PCB and the LED. And quickly I found the culprit: The yellow wire that connects 6V to the carriage had broken off its terminal on the PCB:

I soldered it back on, and now the deck is playing beautifully again! I will play a few more records, and then it should be time to travel back to the UK.

Beogram 4000: Repair of Cracked Hood Hinge

The Beogram 4000 that I recently finished up also had a cracked hood hinge. Sadly, this is a common failure due to the unfortunate way these hoods were designed in the hinge area. The use of countersunk screws in combination with a fairly heavy weight of the hood puts more stress on the plexiglass material than it can handle and often cracks develop over time. This shows how this hood presented:

Fortunately, only one piece broke off making a fairly clean fracture and the rest of the hinge was still in place, albeit with an additional crack between the two bolt holes. I carefully cut through the glue that held the aluminum strip in place using a razor blade. This allowed preserving the strip with little damage:

The next step was cleaning off all the old glue on both sides. This usually works well by soaking the area in isopropyl alcohol for an hour. Then the glue can be scraped off. In this case it worked pretty well:

Then I glued the broken off part back into place with plexiglass glue:

After cleaning up the glue spill out at the crack, I installed Beolover hinge patches. I developed a clamping mechanism that makes use of the two bolt holes to press the patches into the hinge area. The glue usually softens the hinge and the patches can be sunk slightly into the material by tightening the screws tightly:

This is how the outer patch looks like after the glue cured for 24 hrs, and after bolting the hinge back into the hood:

Since the aluminum strip is one of the early 'flimsy' types, the bolt holes need to be 'filled' to make a flush surface with the surrounding plexiglass. Otherwise, the aluminum strip could be damaged if pressure is applied to it from the outside:

Then I applied contact cement to both sides and pressed the aluminum strip back into place after letting the cement dry. Of course, one can see that the hinge has been repaired since the patches add a little to the thickness of the hinge area, and unfortunately, also some glue squirted out towards the front. This is hard to avoid since one wants to make sure the glue really covers the entire patch, i.e. it has to squirt out a bit to  make sure that this happens. But life is mostly a compromise, and so we need to accept that a repaired hood is not as pristine as a new one:

Like pretty much all Beogram 4000 hoods I encountered so far, this one also was missing its rubber bumpers at the front. They usually break off due to degradation of the original rubber material:

I usually carefully (it is easy to crack the thin Plexiglas around the hole) drill them out with a 2mm bit

and then install a 2mm O-ring snippet with some superglue gel:

After letting the gel cure, I cut the snippet to a 1 mm length using a template and a razor blade:

This hood is in business again. I hope it will hold up a while!

Beogram 4000: Complete Functional Restoration

This post summarizes the restoration of a Beogram 4000 that I received a while ago from the UK. A first assessment of this unit is posted here. 

There are two additional 'focus-posts' about this project where I discuss the repair of the AC platter motor Wien-bridge oscillator circuit (which had a bad gain control bulb), and the restoration of the record sensor, which had been tampered with before I received the unit.

This shows the unit as received with the aluminum panels off:

As usual I started out with restoring the carriage. The first step was to extract the components of the arm lowering and carriage transport systems. This shows the arm lowering system:

I removed all the moving parts and also the rods and spindle of the carriage transport:

I cleaned everything in an ultrasonic bath:

Beolovely! While the carriage is 'liberated' it is also the perfect time to tend to the solenoid activated switches. In this unit they were (as usual) bent out of shape and oxidized:

It is best to remove the small PCBs that hold the terminals and then extract the terminals for gold plating. This shows the underside of the carriage. The small PCBs at the bottom hold the switch carriers:

I unsoldered them:

and extracted the terminals:

While the carriage is up it is also convenient to tend to the switches on the carriage position detector PCB. It has five switches, one (green plunger) is the singles position detector which is a break switch. It is especially susceptible to malfunction since only slight oxidation already takes it out of commission (you will notice if the arm is lowered immediately after pressing ON):

I removed the terminals and the plunger assemblies (they are usually full of crusted lubricants). The plungers needed to be cleaned ultrasonically:

This shows the gold plated switch terminals of both solenoid and carriage switches. I coat them first with a Ni film for better adhesion and then with a Co-Au alloy, which is harder than just Au:

Then I re-installed the terminals:

On the carriage position board I also exchanged the solenoid current limiting resistor (red):

These resistors tend to fail since they see some pretty strong currents. I replace them with 2W instead of the 1W specified originals. This shows the rebuilt carriage PCB reinstalled:

Another item to address while the carriage is up is the repalcement of the solenoid transistor. They also have a tendency to fail after almost 50 years. It is bolted to the bottom of the enclosure for thermal management:

I replaced it with a new TIP41C:

Another item to replace on the carriage is the tracking sensor light source, which originally is an incandescent bulb:

This shows the original bulb housing in comparison with the Beolover LED based replacement. In this particular case the original bulb had already been replaced with a non-fitting generic bulb, which had to be 'embedded' into the plastic housing via heat and glue. Whoever did it also got rid of the trimmer that allows adjusting the bulb brightness. Messy. 

This shows the LED replacement in place. The blue box replaces the normally externally installed trimmer for tuning the brightness:

One of the biggest 'standard issues' of the 4000 is their brittle cartridge mount. Most of them have it, and it is a sad moment when it breaks off while removing a cartridge. Usually the plastic tab sticks deep inside the cartridge, and then it needs to be sent off for restoration. Therefore, I replace all of them as a standard item of my restoration packages with a 3D printed nylon based replacement.

I removed the arm from the carriage and had a closer look:

In this case the lower part of the plastic insert that carries the grounding tab was also cracked. I have replacement part for this case, too:

This shows both top and bottom part stuck into a cartridge:

Here you can see how the gold plated grounding tab inserts into the cartridge:

And here is everything together installed in the aluminum tube of the arm:

It is important to make sure that cartridges fit flush with the aluminum tube when installing the parts:

Basically, I use a defunct cartridge (from a sad ebay shipping disaster) to push the glue coated inserts into the tube until the cartridge is flush. Then I let the glue dry and remove the cartridge.

After all these steps I reinstalled the carriage and the arm lowering mechanism and turned my attention to the electronic control system:

First I removed the keypad cluster (if you do this at home, take a few pictures of how the wire harness is coiled under the cluster before you remove it - it can be difficult to get it back in if one does not remember how the fairly thick cable mess is supposed to coil up.

Once the keypad is out, one can turn it around and put the PCB in service position. This reveals the light bulbs and the switch terminals:

The terminals are usually also very corroded and need to be gold plated, like the other ones shown earlier:

I removed them:

and also Ni/gold plated them:

Then I reinstalled them:

This looks much nicer! Then I replaced the light bulbs with LEDs. This shows the Beolover LED boards that replace the scale illumination bulbs:

This is how they install:

The other two bulbs illuminate the RPM trimmers from the back, doubling their purpose as RPM indicators. They can be replaced with standard red LEDs and current limiting resistors. This shows everything in action (at 33 RPM):

After rebuilding the keypad, it was time to tackle the reservoir and motor capacitor bank and the AC platter motor. This shows the original setup:

As so often the main capacitors showed signs of leakage:

This usually leaves behind a mess in the capacitor compartments in the enclosure:

This can be cleaned by soaking in ethanol for a while and then wiping it off:

After removing the capacitors I took the AC motor apart

and inserted the enclosure into motor oil. The enclosure contains the sleeve bearings that I am oil infusing with this procedure under vacuum:

After 24 hrs I extracted the motor parts and cleaned off excess oil. Then I put the motor back together and also installed the new capacitors:

Then I focused on the PCBs. I removed the main PCB. This revealed the two transistors of the push-pull stage that drives the AC motor:

These transistors are also prone to fail, and so I replace them as part of a restoration:

On the PCB I replace the electrolytic capacitors, the H-bridge transistors, the transistors that drive the solenoid main transistor, the transistor that amplifies the record detector signal and the RPM relay and RPM trimmers. This shows the PCB in its original condition:

And with the components replaced:

On the power supply PCB there are only two electrolytic capacitors, which I also replaced:

I usually also replace the light bulb in the sensor arm with a LED assembly:

In this particular Beogram I also had to tend to the photocell in the sensor arm compartment. Someone had tampered with this before and the cell was in a wrong location, i.e. was not able to detect the light reflected by the platter. This disabled the arm sensor. See separate post linked above for more details. This shows the cell back in its proper place:

Which restored the sensor signal to a perfect >3V amplitude:

This Beogram 4000 came with a damaged fuse cover that lost the tab for securing it with a bolt. This is important, since the fuses are at grid voltage, which makes this a safety hazard.

As usual, the fuses had loose contact cups

So I replaced them with new ones:

I designed a 3D printable cover for the fuse box, which I installed to secure the fuses:

Like pretty much all Beogram 4000s this one also had cracked plinth guidance washers. Their exchange requires removing all the bolts that hold the plinth in place. The perfect moment for removing the plinth and re-gluing the loose corner on the right side:

Then I installed the new guidance washers:

This shows one of them in place:

Then I did all the mechanical and electronic adjustments. First I adjusted the floating chassis and the arms height and parallelism. Then came the tracking weight

And arm lowering limit. After taking are of the arm, I adjusted the tracking feedback:

After this it was finally time to give this Beogram its first spin. But no cigar! The AC platter motor spun only erratically. I measured the motor voltage, and received this almost square wave signal.  Normally this should look like a decent sine wave!:

It turned out that this unit had a bad automatic gain control bulb in the Wien-bridge oscillator that drives the AC motor synchronously. After some study and experimentation I was able to replace the bulb with a precision 100 Ohm trimmer and six 1N4004 diodes for gain control. These parts had to be installed on the solder side of the PCB:

This restored a decent motor wave:

Read more detail about this process in the post that was mentioned at the beginning of this report.

Now it was time to do a RPM stability test to verify that the repair had not introduced unwanted instabilities in the oscillator. I did this with the BeoloverRPM device that allows logging the RPM in 10s intervals over extended periods of time:

The curve that I measured is shown in red in this graph:

The blue one is from another Beogram 4000 that still has the original bulb. It seems that the diodes perform as well as the bulb, and that the RPM has a similar stability.

After this I finally focused on the signal path. This shows the original corroded DIN5 plug:

I first installed a new plug and then played the deck, but one channel was missing. It turned out that the cable had a bad lead. So I replaced it with a DIN5 cable from SoundsHeavenly where I removed one of the plugs for installing it inside the Beogram. This shows the nice gold plated plug terminals of this cable:

And here you can see the other end of the cable as installed in the Beogram:

I usually install a switch (red) that allows connecting signal and system grounds in case there are hum issues. This is especially helpful if the deck is used on a RCA input receiver. 

And now it was finally time to enjoy this restored Beogram! I put on a recently acquired CTI record by George Benson, his 1976 live album "In concert - Carnegie Hall" (CTI 6072 S1). Of course this album had been ultrasonically cleaned on a CleanerVinyl ProXL setup using a multi-frequency cleaning protocol enabled by a UC-3360 three-frequency cleaner. This restored the album to a like new quality. I really started liking this album. Especially 'Take Five' and 'Summertime' are great tracks. It also has great recording quality, especially for a live recording. CTI was an awesome label!

This shows the Beogram playing this nice album. A perfect combination!:

Beolovely! Let's see if I can fix the cracked hinge of the plexiglass hood this Beogram came with!..;-). Stay tuned!