Beogram 4002 (5503): Complete Functional Restoration and a Test Spin with Eddie Henderson

This post describes the work done to a Beogram 4002 (Type 5503 with AC platter motor) that I recently received from a customer in Ontario for restoration. This post describes my initial assessment of this unit.

This shows the Beogram with removed platter and aluminum panels:

As usual, I started with rebuilding the mechanical components of the arm lowering and carriage translational systems. This shows the original condition:

I removed all the moving parts:

This shows them ready for cleaning in my ultrasonic cleaner:

I also removed the arm lowering solenoid:

These solenoids are notorious for being permanently magnetized. I removed the plunger from the assembly:

Like many others previously, this plunger was able to attract a small ferrous set screw indicating permanent magnetization:

I used my tape head demagnetizer on the plunger until it did not attract the screw anymore:

This is an important step of any Beogram restoration since a magnetized plunger can result in delayed arm raising. This causes the needle dragging across the platter during the auto-return procedure at the end of a record. Not a happy moment when there is a new $800 cartridge on the arm!...;-)

There is one more moving part in the arm lowering mechanism: The linkage between damper plunger and the little arm that is bolted to the end of the counter weight. You can see it stick out from the V-cut in the arm in this picture:

In order to extract this linkage and to lubricate its pivot point the sensor arm assembly needs to be taken out. This shows the assembly laid flat and the linkage already removed:

Of course, as usual, the small copper plate that facilitates lateral arm movement in up position had come loose after a light tug with my tweezers. It is attached with (now degraded) double sided tape. I cleaned the tape residue off and then glued it back into place with a dab of epoxy:

While the parts were cleaning I replaced the incandescent light bulb in the tracking sensor with a Beolover LED setup. This shows the original black bulb housing still in place:

I removed it, which revealed the aperture used by the tracking system:

This shows the Beolover Tracking Sensor LED Light Source (Beogram 4002 and 4004) in direct comparison with the original part:

The LED is approximately in the location of the bulb filament ensuring drop-in replacement functionality. This shows the part installed:

Then I removed the 'big capacitor mess' and the AC platter motor. This shows the original setup still in place. The phase shift capacitor of the AC motor (leftmost can) had already been replaced at some point:

This shows the empty compartment:

I usually re-infuse the motor bearings with synthetic oil. This requires disassembly of the motor, shown here after removal:

After pulling the pulley and drilling out the rivets I opened up the enclosure:

This is a 'stacked can' motor, which is driven synchronously by a precision oscillator signal. This has the great advantage of being brushless and also very low wow and flutter. The motor bearings cannot easily be removed from the housing halves, so I usually immerse the entire parts in oil and then I pull a vacuum. In this case strong bubbling started immediately:

This indicates air being drawn from the bearing material by the vacuum. As the air gets sucked out, oil can diffuse into the porous bearing material. When the bubbling stops, the bearings are full with oil again, giving the motor a new lease of life. While this process went on I focused on completing the remaining restoration tasks.

In the meantime the mechanical parts came back from the ultrasonic cleaner:

Nice and shiny! When I re-assemble the damper I always put in a new gasket:

As usual, this 5503 had a cracked solenoid switch arm extension:

Luckily there is a Beolover replacement part available, shown here in direct comparison with the original part:

I installed the new extension on the metal arm and secured the small bolt with some epoxy:

It is important that the extension never comes loose, since otherwise the solenoid current may not be lowered after it engages. This would overheat the solenoid in a short timespan.

This shows all the cleaned parts back in position:

I also installed a new Beolover Aluminum Carriage Pulley for Beogram 4002 and 4004:

Then it was time to restore the PCBs. I started first with the two capacitors that were added to the solder side of the main PCB:

This shows the modern replacements in place:

Then I unbolted the PCB and flipped it over:

I replaced all electrolytic capacitors, power transistors, RPM trimmers and the sensor arm transistor and biasing resistor. This shows the PCB after the process was completed:

While the PCB is up it is the perfect moment for replacing the power transistors of the push-pull driver of the AC platter motor. This shows the original TIP31/32 pair in place bolted to the enclosure (for enhanced cooling):

I replaced them with a stronger TIP41/42 pair:

Then I removed the output PCB. It only carries the muting relay and associated circuitry:

This shows the component section in more detail:

I replaced the electrolytic capacitor that controls the relay delay and the Siemens style output relay with a Beolover Siemens Relay Replacement for Beogram 4000, 4002, and 4004:

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

The last PCB needing restoring was the one underneath the 'plexiglass ruler' that is attached to the carriage. This shows the board after removal of the ruler:

This board mainly carries the carriage position sensor as well as the two end switches that detect the end points of the carriage travel. As in many cases the position sensor photoresistor housing had a broken tab. It sits across from the black bulb housing on the board:

I removed the bulb housing

and then I unsoldered the photo resistor. This allowed me to remove the assembly. This shows the orignal photo resistor housing (which in the meantime acquired a second broken off leg) together with the Beolover replacement part:

The new photoresistor inserts in the small 'drawer' that can be pushed into the sensor housing:

This shows the installed assembled sensor together with a 3mm LED that I implanted in lieu of the light bulb:

Here an alternative view after also replacing the solenoid resistor and capacitor:

Exchanging the current limiting resistor is especially important since the original ones are a bit under-dimensioned ad can fail.

This concluded my work on the PCBs. On to the transport locks and cleaning out the enclosure. This shows one of the 'beautifully' degraded transport lock bushings:

It is important to remove all the fragments from these bushings since they can get lodged under the floating chassis impeding its motion. This shows the unit in 'cleaning position' with the floating chassis raised and all removable parts removed:

After cleaning out the debris from the enclosure I exchanged the solenoid transistor. It is bolted to the chassis under the main wiring harness of the deck and can be difficult to exchange when everything is in place. The original units are typically TIP41A power transistors. In this case it had already been exchanged with a different type at some point:

I usually replace them with TIP41C, which is a higher voltage version of the A-type:

My hope is the higher voltage replacements will withstand the rigors of driving an inductive load a bit better. After this exchange it was time to install new Beolover Transport Lock Bushing Set for Beogram 4000, 4002, and 4004:

They are designed as two parts, which makes installation simple. Just put in one half from the bottom

and the other from the top:

Note that sometimes the holes in the floating chassis are a little larger and it can be a good idea to put a bead of super glue gel on the vertical pieces of the parts before inserting them. This shows the new bushing together with one of the lock screws in place:

After re-installing the floating chassis I bolted the wood plinth back in place with a new Beolover Plinth Guide Washer Set for Beogram 4000, 4002, and 4004:

These parts are 3D printed nylon and promise a long service life while enabling a smooth motion of the plinth.

Now it was time to install the Beolover Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x):

This part replaces the original reservoir and motor capacitors, as well as the original wasteful linear 22.8V voltage regulator with a modern buck converter based supply. This reduces the power consumption considerably making the deck run much cooler. The board was designed as a 'drop in replacement', i.e. the solder pads for the wiring are in the approximate locations where they connected originally to the big capacitors. I connected the red and black wires from the rectifier first, followed by the black ground and orange 22.8V power rail wires. Then I connected the green wire that drives the motor:

Next I transferred the purple, dark orange, and orange wires from the voltage regulator to the bottom end of the board: 

The motor bearings had completed their oil infusion at this moment and so I re-assembled the motor and then soldered its four leads to the respective terminals on the board:

Then I bolted the motor in place. This shows the completed installation:

I like to put the original mounting strap across the board. It helps keeping the wiring down and away from the platter. I plugged the deck in for adjusting the platter motor voltage. For this the oscilloscope needs to be connected between the purple motor lead and ground. I adjusted the motor voltage to 5.3V RMS:

This yielded a perfect sine curve without distortions while the motor had a good amount of torque. Perfect! Without an oscilloscope, simply adjust for the lowest setting of the trimmer while still getting good torque. A too high setting will make the motor run louder and much hotter without any benefit for operating the turntable.

Then I adjusted the sensor transistor bias to yield 4V DC at the collector:

After this adjustment, I moved the trimmer to the component side of the board.

There were still three incandescent bulbs to be replaced with LEDs. One of them was in the small compartment inserted into the end of the sensor arm. This shows the compartment pulled out with the bulb still installed. Next to it is the Beolover Sensor Arm LED Light Source (Beogram 4002, 4004 and 4000) together with its alignment aid:

I installed the part:

This shows the LED in action:

The use of a warm white LED ensures a proper back-illumination of the B&O logo.

After working on the record detection system it is always a good idea to check the sensor signal. This is the curve I measured at the collector of TR9:

Each drop in the signal corresponds to a black platter rib passing under the sensor. The amplitude of the signal over an empty platter should be larger than 5V. 7.6V is more than enough and I concluded that this sensor is in great shape!

Next I replaced the two bulbs in the RPM panel. This shows the panel flipped over revealing the two bulb covers:

I removed the covers to access the bulbs:

This shows the removed bulbs together with the Beolover RPM Panel LED Backlights for Beogram 4002 (Types 550x):

The 33 RPM bulb cover showed heat damage caused by the bulb. The LED boards directly solder to the pads of the bulbs forming an extension of the original board:

After putting the bulb covers back into place, I fired the deck up to test the LEDs:

As so often with the AC motor Beogram 4002 the white scale background of the 33 RPM trimmer was wavy causing an inhomogeneous back-illumination. This meant I had to open the RPM panel up to access the scale backs. 

To get in there the four locking washers that hold down the white plastic part need to be cut so they can be pulled off:

Removal of the plastic back revealed the wavy background foil:

The waviness is usually caused by the heat of the incandescent bulb. Since most records are 33 RPM this phenomenon is usually only seen behind the 33 RPM scale:

I usually exchange both background foils to ensure identical looks for both trimmers. I use 3M white electrical tape cut to size:

Then I re-installed the plastic back with four new locking washers and four plastic washers:

This shows the restored 33 RPM trimmer scale:

A very homogenous background! Beolovely!

At this point it was time to do the mechanical adjustments to get the platter parallel to the arms across their range of motion, adjust the platter height relative to the arms and then get the platter flush and centered with the aluminum panel surrounding it. These adjustments can be pretty tedious and iterative until everything is perfect.

Once the arms and platter are aligned the tonearm adjustments can be made. Before I calibrate the tracking weight I usually replace the flimsy circlip holding the counterweight adjustment screw in place (under the red paint in this picture)

with a M3 square nut and a washer:

This allows me locking the calibration in place so it survives the rigors of the shipping process.

Then I adjusted the counterweight to get 1.2g weight at the 1.2g setting of the adjustment wheel:

This scale on the adjustment wheel is notoriously imprecise over its range. Therefore, it is a good idea to calibrate for 1.2g since most B&O cartridges prefer this weight. In general it is best calibrating the weight occasionally with a digital gauge and ignore the scale on the wheel.

Next I adjusted the arm lowering limit. This is an important adjustment since it helps preventing damage to the tip should the arm ever be lowered onto an empty platter due to a circuit malfunction:

The limit should be adjusted that the tip misses the lower parts of the black ribs by about 1 mm. The lower parts of the ribs are located at the 12, 10 and 7 inch setdown points, i.e. where the arm most likely would get lowered accidentally if the record detection mechanism would not work.

After the adjustments were done I performed a 24 hrs RPM stability test using the BeoloverRPM device:

In its 'slow' mode it measures the RPM every 10 seconds and sends the measured value to the serial port of a computer. This allows measuring longterm RPM stability curves. This is the curve I measured after about 24 hrs:

This is an excellent result, but not surprising since this Beogram is an AC platter motor version. Synchronous motors are essentially designed for superior RPM stability. I also measured a curve with the fast mode of the BeoloverRPM device:

In the fast mode it transmits a RPM measurement every time a platter rib passes under the sensor. This yields high-resolution graphs that show short term RPM changes ("wow and flutter") in detail. This graph shows a measurement covering about 60 turns of the platter, representing a run time of about 2 min:

The zig-zag pattern is a measurement artifact that comes from the fact that the spacing of the platter ribs around the platter is slightly irregular due to manufacturing imperfections. This generates a repeating pattern every 24 measurements (there are 24 ribs around the platter), which is superimposed to the real RPM changes. Those are introduced mainly due to the elasticity of the belt that creates a kind of a jo-jo effect between motor and platter motions. The variations are about 0.05%, which is a very good value for this kind of drive system. This motor is definitely ready for duty again!

At this point I was very close to a first test spin. All that was left was replacing the old grimy DIN5

with a new all metal plug featuring gold plated terminals:

Beolovely!

I connected the unit to the Beomaster 2400 that I recently restored and then it was time for a first spin! I selected a recently bought beautiful re-release of one of my favorite Blue Note albums, "Heritage" by Eddie Henderson. This album originally came out in 1976. It was very hard to find until Blue Note recently released an all-analog remaster. In my opinion it sounds excellent. This shows the functionally restored Beogram playing it:

A great contemporary match! This Beogram will still get a new keypad, the Beolover Commander remote control, the Beolover carriage motor upgrade and a new reproduction hood (from the dksoundparts-store in Denmark). Stay tuned!