Beogram 4000: Installation of New Dust Cover and Aluminum Trim

The customer of a Beogram 4000 that I restored in January-February 2025 recently let me know that the new DKsoundparts hood that I installed during the restoration broke off one of the hinges. He included this sad picture:

I decided to replace the cover under warranty since it cannot be ruled out that this was caused by mounting screws that were tightened a bit too hard.

He sent me the hinge. And I installed a new hood and aluminum trim. See here if you are interested in this service. This shows the parts before installation:

First I improved the design of the plexiglass cover by installing small 3D printed plastic bits into the top ends of the 'channels' they designed into the side areas where the aluminum trim is supposed to adhere: 

These channels make it difficult to achieve a perfectly sharp bend with the trim, since it is not supported when it is bent, causing a more rounded corner.

The next step was to check whether there is any interference between the metal back and the plexiglass part when the hinges bend. The new hoods seem generally a bit tighter than the original ones and bent metal hinges can cause interference between metal and plexiglass. The resulting stress can crack the hinge areas of the plexiglass cover. I bolted the metal back onto the hood and checked if the metal would touch the plastic in any way during bending the hinge. On both sides I saw a minimum 1 mm spacing between the parts, i.e. this was a pass:

I removed the metal back again and centered the aluminum trim using my alignment pieces:

I usually use a strip of blue tape to make a pencil mark between strip and the hood:

Then it was time to bolt the metal back in. I put some white wood glue on the threads of the holes in the hinges:

This holds the bolts in place even if they are not tightened very hard.

The final step was applying the aluminum trim

and bending it down on both sides:

Nice precise corners due to my little plastic inserts! Beolovely! Here an impression of the entire dust cover assembly:

Time to send it back to Australia!

Beogram 4000: Carriage Returns Home Immediately After Setting Down on the Record

Oh well, the Beogram 4000 that I restored in January 2025 came back to my bench exhibiting an issue I had not experienced before:

After pressing ON the carriage went and found the LP setdown point and put the arm down. Immediately after hitting the run in groove, the carriage returned home with the arm down. It did that at a fairly high speed. Once home the unit shut off and the arm lifted.

Since the << and >> buttons worked fine with the arm up, a problem with the H-bridge was unlikely. This meant there must be an issue with the tracking sensor.

The Beogram 4000 features two photoresistors FC1 and FC2 that control the reverse and forward directions of the carriage motor (later 4002/4 models are differently set up, with only one photoresistor for the forward direction). This means the dual photoresistor tracking sensor can control the carriage in both directions, forward and reverse. The carriage is at rest when the forward and backward currents through the H-bridge (i.e. the motor) just cancel out. This condition is reached when the aperture in the tracking sensor illuminates both photoresistors with the same intensity, i.e. when it is positioned just between the photoresistors. If everything is properly adjusted, this condition coincides with the tonearm being parallel to the sensor arm. As the arm gets pulled towards the record center during play the arm gets deflected laterally, which causes the forward current to become larger than the reverse current, and the carriage starts moving forward, following the motion of the arm.

A consequence of this setup is that if one photoresistor circuit is not working properly, the carriage motor will already see a significant current even with the tonearm in parallel alignment, and the carriage will start moving. If the failed photoresistor circuit is the one that controls the forward motion, the carriage will always go reverse, independent of the lateral deflection of the tonearm.

With this in mind, I started examining the forward direction circuit. A good rule of thumb with the Beogram 4000 is that 90% of its issues are typically caused by bad contact terminals in the many switches, or by a wiring problem. The Beogram 4000 is an early 1970s design, when wire-to-board connections were still hardwired (instead of using modern wire-to-board headers and plugs, which are mechanically much more resilient). These soldered wires have a tendency to break off at the solder terminals when the Beogram is handled or transported.

This personal 'statistic' was confirmed in this unit: When I had a closer look at the wiring I immediately found the problem. The wire connecting the forward photoresistor FC2 to the H-bridge was broken off at its terminal on the main PCB (yellow marking in the photo):

I cleaned wire end up and soldered it back to the terminal. And the deck was operating normally again! I will play this Beogram a bit and then it should be time for sending it back to its owner in Australia!

Beogram 4000: Installing a New Carriage Motor and a New Hood

Yesterday, I finally received the first batch of my new custom manufactured Beolover Carriage Motors for Beogram 4000, 4002, and 4004. They are a direct drop-in replacement for the original motors, which also suffer from dry oilite bearings, similar to the DC platter motors of the later Beogram 4002 and 4004.

Unfortunately, these motors cannot be opened up very easily for oil infusion of the bearings and therefore I had a suitable replacement motor designed. Since they use modern coreless technology they draw less current than the original motors at the same mechanical performance. This is great news for the often failing power transistors in the H-bridge of the carriage drive. They also vibrate less. Read about the motors here, where I describe my tests of these motors in comparison with an original motor.

This was good news for the Beogram 4000 from Australia that I recently restored. My customer had opted for upgrading his carriage motor and so this project was on hold until I would receive the motors. This shows the original motor still installed:

I extracted the motor:

This shows the upper half of the housing removed and the new motor for comparison:

The new motor is slightly shorter and so the leads can conveniently be fed through the bottom cutout of the housing:

This shows the new Beolover motor installed:

I positioned the motor inside the housing making sure the carriage belt sat straight between the two pulleys. This is easily done since the motor is held in place by two vibration insulating EPDM rubber rings, i.e. the motor can be laterally shifted within the housing if necessary to achieve perfect fit.

This Beogram also still needed a new hood installed. This shows the new hood from the dksoundparts store in Denmark together with a reproduction aluminum trim:

I used the my alignment aids to center the strip

and marked the position with a pencil:

After installing the re-painted hood hinge and glueing in the aluminum trim I installed the hood on the Beogram:

Beolovely! I will play this deck a bit more, and then it will be time to send it back to Australia!

 

Beogram 4000: Installation of a New Precision Machined Solid Teak Frame

I recently received a lovely new CNC machined solid Teak plinth from Christian Hakansson, to be installed on the Beogram 4000 that I recently functionally restored.

Unfortunately, this Beogram had an original plinth that was damaged at the corners (please, watch out for door jambs when you carry your Beograms around!!...;-):

I removed the plinth:

If you do this at home, please, note that there is a 5th bolt under the keypad, i.e. the keypad needs to be removed before the plinth can be extracted. 

The deformed particle board under the veneer suggested that this plinth not only had damaged corners, but also had been in contact with too much moisture at some point in time:

The installation of a new plinth requires that the metal fixtures be removed from the old plinth to be transferred to the new one. I usually wrap the plinth in aluminum foil and then I put it into the oven for an hour at 200-250F. Once it comes out the metal parts can be separated with a suitable spatula or similar:

Once the parts are off, the residual contact cement

needs to be removed. I usually soak paper towel with isopropanol or goo gone and wrap the metal parts in it:

I put aluminum foil around it to prevent evaporation:

After 24 hrs the glue can be rubbed off with the drenched paper towels:

This shows one of the cleaned metal fixtures:

I use ultra thin 3M 300LSE adhesive tape for the installation. This makes the process much cleaner than with contact cement. The tape can be cut out with a razor blade to match the frame shape:

It is important to not cover the little spring tabs that are in the back of the frame:

Otherwise they can get glued to the wood and are not able to perform their duty (holding the plinth in place once it is pushed back) anymore.

Now comes the moment where the metal parts are glued to the wood. This is probably the most difficult task since one only has one try and the parts need to be placed precisely at the right level on the frame. This is greatly simplified by using the aluminum panels of the Beogram. They have the right thickness and can be used to align the metal parts with the frame.

It can be challenging to get the metal parts all the way into the corners since there is adhesive on both sides. I usually deal this issue by using some parchment or wax paper to prevent one side from sticking, while I push in the part all the way into the corner:

This shows one side glued while the other still has the paper in:

Sometimes the metal parts are not entirely conform with the frame in the corners. Many Beograms actually came with this issue 'factory installed'...;-). I sometimes use tongue-and-groove pliers to help seating the metal parts in the corners. Be careful not to damage the frame if you do this at home: 

This shows the new frame with installed metal parts:

And here a couple happy shots of the Beogram 4000 with the new frame installed. Beolovely!!:

Beogram 4000: Full Functional Restoration and a Test Spin with the Ramsey Lewis Trio

This post summarizes my work on a Beogram 4000 that I received from a customer in Australia for a full restoration. An earlier post discusses the condition of the unit as received.

This shows the unit on my bench in 'service position' after removing platter and aluminum panels:

As usual I first focused on rebuilding the carriage:

I removed all the moving parts of the tonearm lowering mechanism

and liberated the carriage from its rods and spindle:

This shows the removed components ready for the ultrasonic cleaner:

A while ago I realized that the plungers in the arm lowering solenoids often have some residual magnetization. If the magnetization gets too strong the arm will sometimes go up with a delay, which can lead to unhappy needle dragging across the record at the end of a record when the carriage returns home. So I made it a standard item of all my 400x restorations to take the solenoid assembly apart

and demagnetize the plunger. I usually test successful demagnetization with an iron setscrew:

If the setscrew cannot be pulled around with the plunger anymore the magnetization is gone.

While the carriage is up, it is the perfect moment for the removal of the solenoid activated switches and gold plating their contact terminals. This shows the three switch assemblies removed from the carriage:

As usual they were fairly oxidized and also bent out of shape from earlier attempts to fix switch malfunctions.

I usually do the gold plating of these switches together with those found on the carriage position detection board that is mounted underneath the travel of the carriage. So when the carriage is removed, it is also the perfect moment to get to the switches on this board. This shows the board still installed:

Unsoldering of the carriage motor leads and removal of two screws allows to flip this board up revealing the switch terminals and the red solenoid current limiting resistor:

I removed all the terminals from the solenoid and carriage switches for plating:

This shows them after first plating them with a coat of nickel followed by a layer of 24 carat gold/cobalt alloy (such alloys are the standard for gold coatings for electronics applications due to their higher hardness)

Beogolden!...;-). Then I soldered the terminals back into their places. This shows the three solenoid switch assemblies

and the carriage position switches:

I usually also replace the solenoid resistor with a modern higher rated power resistor. These old resistors have a habit of degrading and then getting too hot, with following failure. So it is a good idea replacing them preventatively while this board is up.

With this board out of the way it is a good moment to also replace the solenoid power transistor. Originally it is usually a TIP41A:

I this case it was reduced to being a capacitor:

This immediately explained why the solenoid would not activate when I initially tested the basic functions of this unit. I replaced it with a TIP41C, a higher voltage rated cousin of the A version:

This should help allowing this solenoid transistor to survive longer. This shows the carriage PCB installed back in its place. I also cleaned the plastic switch actuators in my ultrasonic cleaner. As so often, they were caked in old lubricants:

Then I re-installed the solenoid activated switches:

Straight and shiny! Beolovely!

While the carriage is liberated it was also a good moment to replace the MMC cartridge mount. Unfortunately, the cartridge tabs of the 4000 series were made from a plastic that has become brittle in most cases after ~50 years. So it is a good idea to replace the mount before it has a chance to break off when a cartridge is mounted or pulled off. Often the broken off tab remains lodged in the cartridge, which can be a hair-raising moment when it happens with a newly restored $800 cartridge!

It is relatively easy to get the original mount out. After removal of the tonearm, it needs to be 'cooked' for ~30 min at a low simmer:

Then the MMC mount can be pushed out with a suitable rod that fits into the aluminum profile. This shows the liberated original mount together with a new MMC Cartridge Mounting Tab for Beogram 4000, 4002, and 4004: 

I transferred the wires to the new part:

and installed it in the arm. It is a good idea to mount the part with a defunct cartridge stuck on the tab. That way the proper position of the assembly inside the aluminum tube is found easily:

After re-connecting the tonearm I replaced the incandescent bulb of the tracking sensor with a LED based assembly. This shows the original black bulb housing still in place:

Removal reveals the aperture used in the tracking mechanism to feedback-control the carriage movement:

This shows the original part together with a Beolover Tracking Sensor LED Light Source for Beogram 4000:

The small surface mount LED is in the approximate location of the bulb filament ensuring reliable functioning of the replacement part. This shows the LED assembly installed:

The small white box on top of the assembly is a potentiometer that allows adjusting the intensity of the LED. This can be helpful when adjusting the tracking feedback gain.

Then it was time to put the mechanical components back together. This shows them nice and shiny after ultrasonic cleaning:

I always replace the damper gasket with a new Beolover Damper Gasket for Beogram 4000, 4002, and 4004:

This ensures a consistent arm lowering speed. The original gaskets are often hardened and/or warped, which can result in undamped arm lowering. Another hair-riser when an expensive cartridge is on the arm!...;-). As usual for later 4000 (earlier units have an all-metal arm), the solenoid arm extension was cracked in this unit:

This extension is crucial for the functioning of the arm lowering mechanism since it activates the switch that reduces the solenoid power after full extension of the plunger. A loss of this extension would cause the solenoid to overheat and short out. Therefore, I always replace this part with a new Beolover Solenoid Arm Extension for Beogram 4000:

If you do this at home, please, make sure you fixate the part, bolt and nut in place with some epoxy. This prevents a loosening of the bolt over time as the part gets 'whacked' by the solenoid every time the arm gets lowered.

After the carriage was in place again I re-lubricated the pivot point of the damper-to-arm linkage. This linkage is mounted on the sensor arm assembly in-between the two arms. You can see it stick out towards the back of the turntable from the small V-cut on the metal plate that is bolted to the back of the counterweight assembly:

For cleaning and lubricating the pivot point the sensor arm needs to be removed. Here you can see it extracted with the linkage already removed:

Af course the small copper plate that helps lateral movement of the tonearm while it is up was loose due to degraded double sided tape. I cleaned the little plate

and reinstalled it with a dab of epoxy.

Then I installed a new Beolover Aluminum Carriage Pulley for Beogram 4000: 

The final 'act' of the carriage restoration was the replacement of the incandescent light bulb in the record detection sensor at the end of the sensor arm. This shows the small sensor compartment pulled out with the bulb still installed:

Next to it is the Beolover Sensor Arm LED Light Source for Beogram 4002, 4004 and 4000 together with its alignment aid. I installed the part:

Then it was time to restore the PCBs. First came the main PCB:

Someone already replaced the original Siemens relay:

I started with replacing the one electrolytic capacitor on the solder side:

Here a picture of the new one:

Then I replaced all the other electrolytic capacitors, power transistors, relay, RPM trimmers and sensor arm transistor:

This shows the new Beolover Siemens Relay Replacement for Beogram 4000, 4002, and 4004 installed:

While the PCB is up, it is a great moment for also replacing the two push-pull TIP31/32 Darlington transistors that drive the AC motor. They are bolted to the enclosure bottom for enhanced heat transfer:

It immediately became clear why the AC platter motor ran intermittently when I first plugged this unit in. One of the pins was broken off inside the yellow insulation tube:

I replaced the two transistors with stronger TIP41/42 for enhanced longevity:

Then I replaced the two electrolytic capacitors on the power supply board and also the sole power transistor on this board:

Next up was were the AC platter motor and the big capacitor cans that serve as power rail reservoirs or to shift the phase of the second motor phase:

I removed everything:

This shows the extracted motor:

I took it apart

and submerged the two clamshell housing parts in synthetic oil. I pulled a vacuum to start the oil infusion of the bearings that are integrated into the clamshells. Immediately strong bubbling and foaming occurred in the oil container:

This process can take up to three days until the bearings are fully replenished. In the meantime I focused on the remaining restoration tasks. At this point most items inside the enclosure were unbolted. So it was a good moment to install new transport lock bushings. The old ones were completely degraded:

This shows the Beogram ready for vacuuming out the enclosure:

The degraded transport lock bushings had turned into a powdery mess:

It is important to remove all the small fragments since they can get lodged under the floating chassis impeding its motion. After the enclosure was clean I installed new Beolover Transport Lock Bushing Set for Beogram 4000, 4002, and 4004:

I designed them in two halves, which makes installation very simple. Just push one half in to the orifice from below

and then the other from the top:

If you try this at home, please, note that some Beograms have slightly larger orifices, which may make it advisable to add a small amount of superglue gel to hold the parts in place. This shows one of the bushings with the lock screw already in place:

Now it was time to install the Beolover Efficient 24V Power Supply and Main Capacitors for Beogram 4000 into the space previously filled with the big capacitor cans:

This part not only replaces the large capacitor cans, it also updates the main power supply of the Beogram, the 24V rail, with a modern buck converter that significantly reduces the energy consumption of the deck and with that also the fairly high heat emissions. Installation is made simple by the clearly labeled contact pads on the assembly. First I soldered the leads from the two 2200uF cans to the pads on the upper half of the board:

Next came the leads that were originally soldered to the reservoir capacitors on the other end of the board:

The oil infusion of the motor had come to completion in the meantime. I re-assembled the motor

and then soldered its four leads to the board:

At this point the board was ready to be bolted in:

The board bolts to the original mounting holes that were used for holding the original capacitors in place.

My next focus was the keypad assembly. It contains an early digital control system that manages the functions of the Beogram. After taking out the sole screw that holds it down I removed it and flipped it over. I saw that the strobe mirror had been already glued back in place. It seemed a solid connection, so I left it untouched:

I also noticed that the lower PCB had been unbolted from its hinge (which allows it to be flipped vertically for service). Luckily the hinge part and the two screws were still in place:

I reassembled the hinge and then put the keypad into service position. This shows the upper PCB that holds all the switch terminals for the keypad. As usually they were very oxidized:

The flipped up board holds most of the digital gate ICs and the light bulbs that illuminate the carriage position indicator and the two RPM trimmers. What I found explains the blueish sheen that came from the position indicator compartment when I initially tested the Beogram. Someone had installed three cold white LEDs:

I focused first on the switch terminals. I extracted them for gold plating. Very oxidized indeed!:

This is how they looked after I coated them with nickel and gold:

Much Beolovlier!...;-).

This shows them re-installed:

Then I replaced the three LEDs and the remaining original bulb with LEDs. This shows the LEDs I use for the backlighting of the RPM trimmers:

They need to be installed with current limiting resistors since they run on the 12V bulb voltage. For the position indicator backlighting I used the Beolover Scale Illumination LEDs for Beogram 4000 LED assemblies. This shows everything implanted:

and lit up:

At this point I also adjusted the bias for the sensor arm transistor to yield a DC voltage of ~1.8V at its collector:

After this adjustment I moved the bias trimmer to the component side.

Then I reinstalled the plinth after bending its mounting tabs back into proper shape. As usual the plinth washers were mostly cracked 

and I replaced them with the Beolover Plinth Guide Washer Set for Beogram 4000, 4002, and 4004:

The black one is for the front center fixture so it cannot be seen when the aluminum panels are installed. This shows one of them installed:

The next step was doing all the mechanical adjustments:

First I aligned the arms to be parallel and in 23mm distance from the platter. Then I aligned the floating sub chassis to make the platter flush with the aluminum surfaces. Next came centering the platter inside the opening in the large aluminum panel. This is done by carefully bending the threaded rods that control the tension in the leaf springs that float the chassis. All this can be a pretty tedious process and require a few iterations to get everything perfectly into place.

Usually, the next step after getting the platter and subchassis adjusted is setting the arm lowering limit and calibrating the tracking weight.

Unfortunately, I realized at this point that the arms after returning home when pressing OFF would not stay home but travel back towards the record for an inch or so until they would stop.

After a bit of thinking I realized that the culprit might be a 24V reed relay in permanent closed position causing the 24V rail to stay on after the carriage hits the off switch at the home position. 

A quick check with the multimeter confirmed my suspicion. The relay was closed even with the deck unplugged. So I extracted it from the coil:

This shows the original relay (top) with the new Beolover reed relay:

This shows the new one installed (top relay in the lower yellow coil):

For more details on the process, please see here.

This fixed the issue and the Beogram behaved normally again.

Now it was finally time to do the remaining adjustments. 

First I focused on the tracking weight calibration. I usually replace the flimsy locking washer on the counter weight screw

with a M3 nut and a washer:

The nut allows locking the calibration in place to survive the rigors of the shipping process.

This shows the final calibration:

I usually try to get the weight calibrated around the 1.2g setting on the small rotary dial next to the arm base. Most B&O cartridges seem to require 1.2g tracking weight. These dials are notorious for showing imprecise weight numbers. In general it is best to use a digital scale for calibrating the weight occasionally regardless the setting of the rotary dial.

Next came the adjustment of the tracking feedback gain to ensure proper tracking of the grooves during the advancement of the tonearm towards the center:

After completing the adjustments I installed a new all-metal DIN5 plug with gold plated contact pins:

Then it was time for my usual 24 hrs RPM stability test with the BeoloverRPM device:

This measurement (done in the 'slow' mode of the BeoloverRPM) yielded this 24 hrs RPM stability curve:

This curve shows the typical thermal drift that is typical for analog control systems. My workshop in Albuquerque changes temperature quite a bit during the night in winter due to the often freezing outside temperatures. The dip in the graph above corresponds with the unheated night hours in that room. Overall this curve is as good as it gets with the Beorgam 4000! 

The BeoloverRPM has a second mode, 'fast', where it puts out one RPM measurement per platter rib passing under the sensor. This allows a high resolution measurement that allows the determination of 'wow and flutter', in other words RPM changes that occur on a short timescale.

The fast mode usually results in an RPM graph that shows a repeating pattern:

This pattern repeats every 24 measurements, i.e. corresponds to the turns of the platter (the platters have 24 ribs on them. Every platter yields a different pattern suggesting that this pattern is a measurement artifact. Indeed there are small differences in the rib spacing around the platters due to manufacturing tolerances and this imprints a pattern on the RPM measurement. This graph shows the pattern for about 50 latter turns:

The slight superimposed waviness of the pattern actually corresponds to real RPM changes caused by the elastic coupling between platter and motor and fluctuations in the precision Wien oscillator itself that drives the synchronous motor. These fluctuations are well below the 0.05% RPM variations specified in the Beogram 4000 service manual. So all good in the RPM department of this Beogram!

Not all good was the record detection department. After the above test I did my usual test with an empty rotating platter to see if it would properly detect that there is no record. It did not and eagerly dropped the needle onto the platter! It turned out that the photocell in the sensor compartment at the end of the sensor arm had delaminated. I extracted the defect cell:

Sadly, this is an increasingly occurring issue, probably due to old age. For this reason I recently designed a modern replacement based on silicon photo diodes. This is a picture of the new Beolover Sensor Arm Photocell for Beogram 4000, 4002, and 4004:

It is a direct plug-and-play replacement for the original cell, i.e. there are no circuit modifications necessary to make this work. This picture shows it installed:

Please, read my dedicated post about the installation process for more details. After installation I qualified the sensor response with my oscilloscope. This shows the trace I measured above a rotating platter:

A very good signal with a 2.5V amplitude. More than what the manual specifies. A test with an empty platter confirmed that the record detection mechanism indeed was restored.

At this point I finally tried to play a record. It played, but only on one channel. Closer inspection yielded that one of the thin wires that connects the tonearm had broken off:

I was able to solder the two wire pieces together, which restored the second channel:

Please, read my dedicated post about this microsurgery for more details about the process.

Now it was finally time to install the Beolover internal RIAA pre-amplifier for Beogram 4000. It is a pretty simple installation process. It connects directly to the output terminals of the Beogram and the output cable only needs to be transferred unmodified to the equally spaced output terminals of the RIAA board. This shows it installed:

Read more about the installation process here. The board can be switched between RIAA amplified and un-amplified standard signal routing. This means after installation the deck can be directly used with any high-level input like DVD, CD, AUX or any modern boombox with a line input, while it also can still be used with a dedicated Phono input.

And then it was finally time to enjoy a first record on this beautiful fully functionally restored Beogram 4000! I chose a recent acquisition, a pretty awesome record released 1972 by the Ramsey Lewis Trio on Columbia Records (KC 31096). I bought this record as 'bycatch' when I was ordering another record on discogs and free shipping was offered by the seller for a couple more records from his store. And so I went through the collection and fund this one. I am happy I did! It has a very interesting rendition of one of my favorite tunes, People Make the World Go Round on side one.

Of course this record was cleaned on a CleanerVinyl ProXL setup to restore its original glory.

Here an impression of this lovely album playing on the Beogram:

Absolutely satisfying! I will now play this Beogram 4000 in my shop for some time while we wait for the arrival of a new CNC precision machined teak wood frame provided by Christian Hakansson's workshop. Unfortunately, the original plinth is damaged on the front left corner. Walk more carefully, people, when you carry your Beogram around!..;-). Stay tuned for an update!