Beogram 8000 (Type 5613): Replacing the Tracking Sensor Light Bulb with a LED Assembly

Recently I was able to buy a Beogram 8000 in fairly decent cosmetic condition. I thought I would restore it and then offer it for sale. After completing the basic functional restoration tasks (stay tuned for my report on the work I did) I had to realize that the tracking sensor light bulb had a broken off wire and so the unit did not track anymore.

So be it I thought. I do not really like incandescent bulbs anyway. They change their emission characteristics continuously over their short lifetimes, i.e. they are always good for some trouble. So replacing them with LEDs is usually a good idea. 

Since this was the first instance of a broken tracking bulb in a Beogram 8000 for me, I did not have a ready to go replacement. So it was time for a bit of creative development work!...;-):

This shows the compartment under the arms where the tracking sensor resides:

After a communication with co-Beolover Sonavor I understood how to get in there. He had done it before. Standing on the shoulders of giants!...;-). One can simply lift up the cover plate a bit until it clears the pin that holds it in place and then slide it out. This shows the compartment opened up:

Here more magnified: 

Photoresistor and bulb are mounted on a small PCB in the back, which connect s them through four wires to the rest of the circuit. These wires come out at the bottom of the compartment and are pretty tight. Luckily one can remove a couple rubber washers that hold the wires in place and then they get a bit looser:

This allows pulling out the small PCB just enough so one can access the solder side:

Here a more detailed view of the backside (bulb already removed):

The red and black wires power the bulb, with the black being GND and red 15V. The hole is sized to hold the bulb base whose wires are then soldered to the two solder pads around the hole.

First I thought I would build a prototype LED board using protoboard to fit into the orifice to replace the bulb. Out came the Dremel and I made a little board that fit:

The plan was to mount a LED and an appropriate resistor on this board and then make the connections to the small PCB. When I debated which LED from my stash to use, it dawned on me that the LED circuit on my standard Beolover Tracking Sensor LED Light Source for Beogram 4002 and 4004 would fit the bill perfectly if the adjustment trimmer connected in series would be removed. In Beogram 4002/4004 the bulb runs at 21V, while here in the 8000 it is powered from the 15V supply. Without the trimmer I thought I would probably get a very similar light output from the LED! So I Dremeled one of the 4002/4004 boards to have the right form factor while still sporting both LED and current limiting resistor. I used magnet wire to make electrical contact. Here you can see the end result in comparison with the bulb:

The narrower end of the board on the right is just about as wide as the bulb base.

This shows the board stuck through the orifice and soldered to the pads:

A view from the other side:

And everything pushed down into the compartment and powered up:

The LED is located in front of the lens at a similar position like the original bulb filament.

The final step was putting the wiring back into place so it would not chafe with the floating chassis base during carriage movements. I pushed the wires back where they were and installed the two rubber discs that hold them in place:

Then I put my test cartridge on the arm and the record that I use for tracking feedback adjustment on the platter. I dialed in the tracking aperture to get about 2-3 rotations of the platter before the carriage starts moving after putting the arm down. Everything worked perfectly! A good afternoon at the Beolover bench!...;-).

This shows the tracking sensor in action:

Records played perfectly with it! 

After this successful prototype development I sat down and designed a more professional PCB that should make the bulb replacement a snap. It is currently in production and I hope there will soon be a new Beolover part available via my store.

Stay tuned for the description of the other restoration task that I performed on this lovely Beogram 8000!

Beogram 4000: Return to the Bench for an Upgraded Power Supply and New Carriage Motor, and some TLC

A Beogram 4000 that I restored in December 2022 returned for the installation of a Beolover Efficient 24V Power Supply and Main Capacitors for Beogram 4000 board and a new Beolover Carriage Motor for Beogram 4000, 4002, and 4004. It also needed the tracking feedback re-calibrated.

The unit arrived safely in its Beolover shipping container. Unfortunately, the keypad was only taped down with a single strip of blue tape and so the center pad came loose on one end:

Luckily, this is an easy fix if one takes out the keypad from the enclosure so the keys can be accessed from the side. Then, after removal of the ON/OFF key the spring of the main key can be re inserted from the side using a suitable screwdriver. After the main key was back in I re-installed the ON/OFF key using the same method:

I set out to install the new Beolover Efficient 24V Power Supply and Main Capacitors for Beogram 4000 board. Here you can see my original setup using a 3D printed plastic part to hold new regular capacitors in place. On the left is the new replacement:

This board does not only replace the big capacitors, but also replaces the inefficient 24V power supply with a modern buck converter that has a much smaller loss. Consequently, the deck will run much cooler and use less energy once the board is in place.

The first step was to remove the old setup and also the platter motor:

Then the new board could be soldered in. Simply follow the color labels on the new board for soldering in the leads if you try this at home. I usually start with the ones in front, connecting the 24V rail as well as the solenoid power (thin blue wire) and platter motor power (brown):

Then I usually do the 6V system in the back (yellow/blue and two black GND connections):

The final step is re-connecting the motor. I usually do the phases (purple/green) first since the wires are longer, i.e. the motor can still be removed while soldering them in:

The final connections are the GND connections of the motor phases which go to the large black/green/GND labeled field. For this the motor needs to be bolted in since the leads are usually pretty short:

This shows everything back in place:

Nice and clean! After a brief function check I focused on the carriage and tracking. The first step was coating the carriage rods with Tactikel NST, a high-tech coating based on nano-particles for making the rods more slippery. I started doing this since the owner of this Beogram 4000 reported excellent results when he used this product on his other 4000. And I have to agree, it seems to help the smoothness of the carriage transport resulting in less choppy carriage motor action. I removed the rods the carriage travels on

and rubbed the coating on. It needs to cure for ~ 2hrs according to manufacturer instructions:

After the 2 hrs were over, I wiped the rods with a soft cloth and re-installed them.

On to replacing the carriage motor with a new Beolover Carriage Motor for Beogram 4000, 4002, and 4004. This shows the original motor:

I unsoldered the leads and opened up the enclosure:

I installed the new motor:

The new motor is a bit shorter, i.e. the leads can be fed through the opening in the bottom of the enclosure. This makes for a clean installation:

Note that I had to reverse the leads to get proper directionality of the new motor. The original motor was one of the small subset of motors with an opposite polarity. I powered the deck up and tried the new motor. So much quieter than the original one! Beolovely!

On to calibrating the tracking feedback! It turned out that the tracking sensor aperture attached to the tonearm base had moved a little bit. Probably during a transport event. I adjusted everything to get 2-3 rotations before the carriage starts moving after setdown. And then it was time to give this deck a test spin! 

I selected "One on One" by Bob James and Earl Klugh (CBS 83931), currently one of my favorite records. A perfect companion for this lovely Beogram 4000! Of course this vintage record was cleaned on a CleanerVinyl ProXL setup to restore its original sound!

I will play this Beogram a bit more and if nothing else comes up it will be time to return it to its owner!

After this happy moment my customer reminded me that the arm lowering mechanism could use a new damper gasket. Back when I restored this Beogram 4000, I did not understand yet that these gaskets should be replaced. They are often hardened or bent out of shape, which can make the arm lowering process inconsistent.

This shows the damper (right) and the solenoid (left):

I removed the damper and took out the plunger. This shows it with the original black gasket in place:

I removed it and replaced it with the new Beolover part:

I realized this unit also still had the original plastic solenoid arm extension. Most of them have developed cracks over time around the rivet:

Once the plastic part separates the solenoid coil overheats and often needs to be replaced. I designed a replacement part, the Solenoid Arm Extension for Beogram 4000:

This shows it installed on the metal arm:

And here a picture of the arm back in place:

Beolovely! 

Beomaster 6000 (Type 2253): Runs Too Hot, Output Stages Rebuild, Volume Belt Replacement, and Repair of an Intermittent Power Supply

A few months ago I met a couple while riding my bike around in my neighborhood in Albuquerque. It turned out that they lived close by. And that they have close ties to Denmark. The plot thickens!...;-). Long story short, I was invited to look at a Beomaster 6000 (Type 2253) that they bought in the 1980s from a local store. It was running hot and the volume could not be adjusted anymore.

Recently they went on a trip for a month and it was a good moment to give it a bit of TLC. So I picked the unit up and put it on the bench:

It is in pretty good cosmetic condition. Only very minor damage to the veneered side panels:

I put the unit into service position (which was easy since the plastic enclosure screw fittings had broken out - see below for my repair of this issue) and had a look at the volume servo:

As expected the rubber belt was gone. Luckily, this is an easy repair if one knows that the pulley on the string mechanism can be pulled off for installation of a new belt:

So with a bit of care the new belt can be installed without needing to mess with the string that moves the volume indicator foil. I put a Beolover Volume Servo Belt for Beomaster 6000 on the shaft:

and after pulling it onto the motor pulley:

I turned the unit on to test the volume drive. I noticed that one of the two light bulbs that illuminate the volume scale was dead:

I replaced it with a red LED and an appropriate resistor:

Once I had figured out what resistor to use for a good intensity I also replaced the still working bulb:

This is how it looks like with the scale bezel installed:

Beolovely! On to the other major issue, the hot heat sink. I removed the metal shroud from the heat sinks, which revealed the output amplifier board. It is bolted to the heat sink, which cools its output transistors:

Removal of two screws from below releases the entire assembly and it can be pulled up:

I unplugged it and put it on the bench:

After removal of the screws that hold the board to the heat sink, the board can be flipped up so one can access the solder side:

I usually replace all the electrolytic capacitors and the quiescent current trimmers. This Beomaster was one of the initially produced units, which have two non-polar electrolytic 47uF capacitors installed. They are evident by the absence of polarity markings:

In later production runs of this design they were replaced with back to back standard polar units and a slightly modified board to accommodate them. Of course I did not have any non-polar 47uF electrolytic capacitors since they are a special item. But I have a wide selection of surface mount components for my development work. So I made two small adapters for standard SMD multilayer ceramic capacitors in a 1210 package using small Dremeled pieces from a development board and male board headers:

This shows one of them installed:

Next came the quiescent current trimmers. They are a bit of an Achilles heel of this amplifier design since they can lead to overheating output transistors when they oxidize as they age. Oxidization can increase the resistance across them and higher resistance means more quiescent current through the transistors, even if no music is playing. In the extreme, these trimmers can go open circuit and then smoke will come from the heat sinks, followed by a shutdown of the receiver due to blown fuses. I removed the two trimmers for the left and right channels and measured them. Unsurprisingly, one of them yielded a fairly high resistance of around 80 Ohms:

Normal is maybe 60 when they are adjusted properly. I replaced them with modern encapsulated 25-turn trimmers, which allow a much more precise and long-term stable adjustment of the current. Before the installation I made sure they were set to a resistance lower than 50 Ohms (usually, trimmers come set to center from the factory, i.e. in this case of 100 Ohm trimmers they should be set to around 50 Ohms, but it is a good idea to check):

Then I soldered them in. This shows the restored board together with the evicted original parts:

I plugged everything back togehter and turned the unit on. Then I adjusted the trimmers to get 22 Ohm (cold receiver) between the emitter resistors of the output:

this concluded my work on the output stages. In this vintage B&O it is a good idea to also replace the electrolytic caps in the power supply. They also get pretty warm. They are often out of spec due to leakage or drying out. The power supply is to the right of the output stages using the remaining heat sink real estate in the 'chimney' in the back of the enclosure. Removal of another screw from below the chimney liberates this board with its attached heat sink. This shows it in original condition. Two of the reservoir capacitors are mounted directly on the board. They are the two big cans in the center:

I replaced them with a couple new replacements:

The next step was replacing the two main reservoir cans (that stabilize the output stages) sitting in their own separate compartment next to the power supply board:

I installed two Beolover Reservoir Capacitors for Beomaster 6000 and 8000, which use 3D printed adapters to give modern capacitors the same form factor like the original ones: 

Assembled:

This makes transferring the wiring a snap. I removed the original capacitors with their ground connection still intact:

Then I transferred the ground wire to the new assemblies keeping the orientation of the terminals about the same:

Then I put the connected cans into their compartment and soldered the power rail wiring back on:

This concluded my work on the power supply (or at least so I thought at this point!...;-) and I focused on repairing the broken out enclosure screws. This shows the 'as-received' situation on the right side

and on the left side of the enclosure:

(I put the screws and nuts where they need to be when in their unlocked position).

A typical issue of this generation of B&O designs from the early 1980s when plastic was king (remember the 1981 Plymouth Reliant? What breathtaking progress in the automotive sector!!...;-). Luckily, 3D printers were invented since, making repairs of such design sins a bit easier. I designed parts that fit on the remaining stumps. This shows the right side component including the original bolt and square nut:

This one needed to be epoxied to the remains of the original fixture for lack of space. I used two toothpicks against the circuit board to hold the part in place while the glue cured:

This shows the corresponding part for the left side:

On the left there is some space below the fixture that can be used for putting in a bolt. I drilled a hole through the bolt orifice in the part for precise fit:

Note that this photo shows an earlier version of the part, which had to be modified later since the left side has much less space available due to a metal bracket that is bolted to the mating area on the bottom part of the enclosure. This shows the final part in place. I also used epoxy to fuse the part as good as possible to the stump, while the bolt gives it additional structural stability:

A shot from a different angle:

At this point I thought I was done and I set the Beomaster up with a Beogram 4002 that I just restored to listen to a record.

Sadly, I was not able to turn the Beomaster on anymore. Something had happened between my bench and the sideboard where the Beogram was! Frustrating! The symptoms were these: I plugged the unit in and the lights under the volume indicator came on, and I also heard the click from the relays. But otherwise it was completely dead: Nothing on the displays, no power dot, no response to the keypad. Nice! Exactly what one wants to happen when fixing something!...;-).

I opened it up and had a look around. My earlier experience with units from this B&O vintage suggested a cracked circuit board, a cold solder joint or a broken board wire (they often disconnect right at the soldering tab within the insulation, and therefore one cannot see it when it happens). I started 'wiggling things' and after a while the power dot in the display came back on and I was able to turn the unit on again by selecting an input source button on the keypad.

Some more wiggling things and I was pretty sure that the power supply board (16) was the culprit. Not surprising, since its voltage regulating transistors are bolted to the heatsink, while also soldered to the PCB. This is generally a solid recipe for getting faults like this since the solder points can easily get damaged due to thermal expansion strain or just vibrations of the heat sink against the board when moving the unit, like I did.

Indeed it turned out that the fault could be reliably provoked by bending the board a bit against the heatsink. So my first response was to re-solder all the sink mounted transistors. But this did not fix it. So I thought it is probably a cracked trace close to the transistor solder points. I soldered short magnet wire (which has a heat removable polyurethane coating) pieces to the transistor solder points and made direct connections to the next circuit node, thereby circumventing the traces in close proximity to the points. Sadly, this also did not affect a change. At this point I started bending the board a bit more 'selectively', i.e. just on one end and then the other trying to get some insight into which area of the board might be affected. It seemed to me after a while that the left side of the board was a bit more sensitive. So I soldered some more wire bits between connected nodes and this finally cured the problem! I was now able to bend the board in any direction I wanted and the unit stayed on! This shows the final result of my efforts:

It was finally time to enjoy a record through this Beomaster! While I listened to it, I noted that I was not able to lower the volume below maybe 10% on the volume indicator. Even the '0' button of the volume presets did not mute the sound. In theory one should be able to lower the volume to zero with the volume up and down buttons. So I opened it up again and had a look. The problem became clear quickly: the volume indicator foil had an issue to go all the way to the quiet end, and due to this blockage, the motor was not able to drive the volume potentiometer all the way to its end point. 

This shows the volume indicator foil as it appeared to me at this point:

If you look closely at the right end of the foil mechanism, where the white string connects, it is apparent that the white 'plate' that connects to the string hangs down a bit before the plastic bracket that keeps the ribbon on track. And that prevented the foil from being pulled all the way to the end. I figured the white piece could use something like a ramp to guide it up a bit, so it could move all the way up to the plastic bracket. I 3D printed a few shapes that did not obstruct access to the solder points underneath the ribbon but were able to act as a ramp. This is the shape I ended up using:

It seems to work well and now the white pice makes it to the end of its travel every time zero volume is dialed in:

Here a photo from a different perspective:

Ok! Back to some more testing of this Beomaster 6000! I will play it for a while to make sure there are no more intermittent issues!