beolover: Beogram 4002 (5503): Full Functional and Cosmetic Restoration of a Unit Rescued from Ebay

This post describes the work done during the restoration of a Beogram 4002 (Type 5503 with AC platter motor) that I was able to purchase recently. My initial assessment of this unit is posted here.

This shows the final result of my labors:

Looks nearly new and also plays like new! Beolovely! This Beogram is available for purchase at the DKaudiolover store.

Let's see what it took to get there:

This shows the unit after removal of the aluminum panels and platter:

While the AC platter motors are less troublesome than the later DC motors due to their brushless stacked can design, they also have issues with drying out Oilite shaft bearings. Dry bearings often cause them to 'knock' while driving the platter. Therefore, I also re-infuse their motor bearings with oil under vacuum when I restore this Type. This shows the AC platter motor together with the original big capacitor cans that serve as motor coupling and phase shift capacitors, as well as reservoirs for the main circuit:

I removed it all leaving behind a bunch of orange transport lock bushing fragments:

This shows the extracted motor:

It has four leads since it is a two-phase synchronous motor. I took it apart to prepare the motor enclosure halves for oil infusion:

It is impossible to remove the motor bearings without doing significant damage, so I simply submerge the entire motor housing in synthetic oil making sure that both bearings are completely in the oil:

After pulling a vacuum one can usually see air bubbles coming from the bearings in the center of the pieces. This indicates that air is drawn from their porous bearing material making room for oil to diffuse into the material. When the bubbling stops the process is complete and the bearings are ready for another tour of duty.

While this process was underway, I focused on the other restoration tasks. First came the restoration of the carriage. The arm lowering and carriage motion mechanisms usually suffer from hardened lubricants. Therefore it is a good idea taking it all apart for a good cleaning and re-lubricating. This shows the original encrusted setup:

A detail shot of the as usual cracked black plastic carriage pulley:

I removed all moving parts:

It is a good idea to rest the carriage on a soft pad to protect the delicate wiring at its bottom.

This shows the removed parts ready for the ultrasonic cleaner:

Aside from cleaning and re-lubricating it is also a good idea to de-magnetize the solenoid. If the plunger is magnetized it can lead to delayed arm raising, which can cause the needle dragging across the platter during auto return after playing a record. Not a fun moment when a newly rebuilt $800 cartridge is mounted on the arm! This shows the extracted solenoid:

The removed plunger was indeed magnetized. It was able to attract a small M3 iron set screw:

After treating it a bit with my tape head demagnetizer the setscrew was able to stay put even at very close distances:

In the meantime the parts came back from the ultrasonic nice and shiny:

I started re-assembling everything. It is a good idea to install a new damper gasket:

The old ones are often hardened and/or deformed, which often causes inconsistent arm lowering speeds. Another 'fun moment' when the nice new cartridge occasionally crashes on the platter without damping!

An 'Achilles heel' of the AC motor Beogram designs is the solenoid arm. It has a plastic extension that is riveted to the metal arm. Like most Beograms of this Type this unit had also already developed a crack in the plastic around the rivet:

This is a dangerous issue since it often leads to a burnt solenoid coil if the problem is not addressed in time. When the extension finally breaks off, the solenoid switch is not actuated anymore after the solenoid lowers the arm. This causes the solenoid current to flow full strength while the record is playing. After a few minutes the solenoid then gets hot enough to melt its spool and the polyurethane wire insulation. The process ends with a massive short circuit that blows the fuses.

I always install a 3D printed Beolover Solenoid Arm Extension for Beogram 4002 (Types 5503, 5504). This shows the new and the removed original cracked part in comparison:

I bolted the new part in place and used a good amount of epoxy to fix everything in place:

The epoxy is an important part of this installation. The plastic extension needs to be attached very well and securely.

The next step was updating the solenoid switch. I now always replace these switches as part of my standard restoration 'package' since I had an unnecessary warranty call last year when a 5503 that I sold earlier in the year came back with a broken solenoid switch. These switches are a bit under-dimensioned for the task since they need to break currents of 3 to 4 amps every time the arm lowers, while they are only rated for 2 amps. I guess B&O accepted a bit of 'planned obsolescence' here assuming the switches would not see enough switch cycles over the expected 10-15 year product life-time to cause significant trouble.

This shows the original solenoid switch board sill in place (together with the rebuilt solenoid arm):

I unsoldered the three leads and removed the board:

This shows the board with the new (white) switch installed:

There was another cracked original plastic part, the spindle nut holder. It usually breaks around the bolt hole due to over-tightening. This shows the partially cracked original part next to the new Beolover Spindle Nut Holder for Beogram 4000, 4002, and 4004:

This shows the new part installed:

It bolts in with the original screw.

This shows the entire setup back together:

Here a picture of the new Beolover aluminum carriage pulley:

Beoshiny! There was one more pivot point left in need of cleaning and re-lubrication: The damper to arm linkage! It is mounted in-between the tone- and sensor arm assemblies. You can see it stick out from the v-cut in the small metal linkage that is bolted to the back of the counterweight:

In order to get to it the sensor arm needs to be removed. This shows the sensor arm lying on its side with the linkage already removed:

Of course the small copper plate that helps the arm move laterally when up came loose with only a light tug with my tweezers. I epoxied it back into place after re-assembling the arm:

The next step was aligning the sensor arm base and the sensor arm itself orthogonally relative to the rods the carriage travels on. I did this using my recently developed Beolover Arm Alignment Tool for Beogram 4000, 4002 and 4004:

It streamlines the process considerably compared to eyeballing the alignment, which I did before I came up with the tool.

Next I replaced the original incandescent bulb of the tracking sensor with a Beolover Tracking Sensor LED Light Source (Beogram 4002 and 4004). This shows the original setup with the black bulb housing still in place:

I removed the bulb housing, which revealed the tracking aperture:

It permits more or less light onto a photo resistor, which drives the carriage motor to keep the light intensity constant. This shows the original and new parts next to each other:

The small SMD LED of the Beolover part is in the same spot like the filament of the bulb enabling a smooth drop-in replacement process:

This completed my work on the carriage and I moved on to restoring the main PCB. It usually has two 'after-thought' capacitors installed on its solder side:

I replaced these two tantalum capacitors with modern units of like value

and then I unbolted the board and flipped it over:

I replaced all electrolytic capacitors and power transistors, as well as the RPM trimmers and the sensor arm transistor (which is usually out of spec and does not have enough gain anymore). This shows the rebuilt board together with the extracted old components:

While the board is up it is a perfect moment for replacing the two TIP31/32 transistors of the AC platter motor push-pull amplifier stage. They are bolted to the bottom of the enclosure for efficient heat dissipation:

I replaced them with new and stronger TIP 41/42 packages:

Next I removed the keypad assembly and took the output board out:

It carries the output grounding relay and its time delay circuit:

I replaced the relay with a new Beolover Siemens Relay Replacement for Beogram 4000, 4002, and 4004 and a new capacitor for the delay circuit:

I also installed a (red) switch that allows connecting signal and system grounds if there is a hum in the audio signal. Connecting the grounds usually fixes such issues.

At this point pretty much everything had been removed from the enclosure except the floating chassis itself. This made it the perfect moment for fixing the decayed transport lock bushings. This unit had lost them completely. This shows one of the transport locks partially dismantled:

While the floating chassis is out it is a great moment for replacing the solenoid transistor, which is bolted to the bottom of the enclosure:

This shows the floating chassis removed for cleaning out the enclosure. It had a lot of transport lock fragment strewn around:

I gave it a thorough vacuuming and then implemented new Beolover Transport Lock Bushing Set for Beogram 4000, 4002, and 4004:

They install very easily since they are designed in two parts. Simply insert one half from the bottom and the other from the top:

Note that some Beograms have slightly bigger transport lock orifices than others and it can be a good idea to glue the lock bushing halves in with a small amount of super glue gel on the vertical parts. This shows one of the bushings with the transport lock bolt in place:

I also installed a new solenoid transistor:

I usually replace the original TIP41 with its higher voltage cousin TIP41C hoping for some more longevity.

The next step was the installation of the Beolover Efficient 22.8V Power Supply and Main Capacitors for Beogram 4002 (Types 550x) board:

It elegantly replaces the original big capacitor mess and also gives the Beogram a modern precisely controlled 22.8V power rail that is much less wasteful than the hot original linear voltage regulator setup. This means the Beogram will consume around 30% less energy than before when this board is installed. The board fits into the space previously occupied by the big capacitor cans and uses the same bolt holes:

I usually solder all the non-motor leads into place first:

followed by the motor wiring:

This shows everything in place:

I usually bolt the original mounting strip that held the capacitors in place back in. It nicely keeps the wiring down so it does not scrape on the platter later.

There were still a few light bulbs that needed replacement. First I replaced the one in the sensor arm. This shows the small compartment pulled out with the original bulb still in place:

Next to it is the Beolover Sensor Arm LED Light Source (Beogram 4002, 4004 and 4000) together with its alignment aid. When I removed the bulb it became immediately clear why the sensor did not work anymore. The bulb had lost one of its leads to corrosion:

I implemented the LED board:

and then tested it:

It is based on a warm-white LED which emits enough red photons to illuminate the B&O logo in a nice warm incandescent sheen.

Two more bulbs that need replacement are in the RPM adjustment panel above the keypad. This shows the panel flipped on its front, which reveals the two bulb covers:

I removed the covers:

As usual the 33 RPM cover had heat damage, as is evident from the brownish discoloration on its inside. I replaced the bulbs with Beolover RPM Panel LED Backlights for Beogram 4002 (Types 550x). They solder directly to the points where the bulb leads went:

Here a detail shot of one of them:

The little boards essentially act as extensions of the original circuit board.

I tested the LEDs and as expected the white background behind the 33 RPM trimmer scale was wavy:

The background foils also suffer heat damage from the hot incandescent bulbs. I removed the plastic assembly from the front plate, which revealed the foils. Indeed the 33 RPM side was wiggly:

I replaced the foils with 3M white insulating tape cut to size:

A second test after reassembly showed a nicely homogeneous background:

Beolove is in the details!...;-).

The remaining incandescent bulb in the 5503 is on the carriage position PCB under the plexiglas 'ruler' that is bolted to the carriage. This shows it after removing the ruler assembly:

First I replaced the solenoid resistor and the decoupling capacitor of the position sensor photoresistor. This shows the two new components in place together with a rear view of the black position sensor components:

The black housing on the right conceals the light bulb in the sensor. This photo shows the bulb after removal of its housing:

I usually replace the bulb with an amber LED and a current limiting resistor:

The next step was adjusting the bias of the sensor transistor to yield the service manual prescribed 3.0V at its collector:

After the adjustment I moved the trimmer over to the component side of the board:

Then I checked the sensor response with my oscilloscope. This shows the collector voltage with an empty platter spinning underneath the sensor:

Each dip in the curve corresponds to a black platter rib passing under the sensor. The measured amplitude of 6.7V is an excellent result. The record detection circuit was working very well in this Beogram!

While I had the oscilloscope fired up I also measured the motor signal. This shows how I connected my probe:

The measured signal was a perfect sine-wave. I adjusted the motor voltage trimmer to get 4.6V RMS and the 33 RPM trimmer to yield 43 Hz frequency:

I also adjusted the 45 RPM trimmer to get 57 Hz:

These frequencies are not precise but they closely correspond to 33.33 and 45 RPM.

This unit probably spent some time in an attic or basement. All the external wiring was gnawed on by some hungry rodents. This shows the output cable:

It also had a very grimy corroded DIN5 plug:

I had a good condition output cable without rodent bites in my stock. I installed it in lieu of the damged one and also put a new all-metal plug on it with gold plated contact terminals:

Beogolden! Next came the replacement of the dangerously damaged power cable which had some stretches with exposed copper:

I soldered in a spare cable that I had rescued from a parts unit that I was given at some point in the past:

I had to remove the fuses to be able to solder the new cable to the contacts in the fuse box. When I popped them out of their holders one came apart:

This is a common failure of the original fuses and it is generally a good idea to replace them with new ones whenever a Beogram is restored:

After fixing the wiring it was time to the mechanical adjustments. In order to do this the aluminum platers need to be installed, which made it the perfect moment for installing a refurbished keypad to replace the badly damaged original one. This shows the original keypad (left) in comparison with a newly restored keypad:

Please, see here if you are interested in fixing your keypad or let us rebuild it for you.

I also re-installed the nice condition original wood frame. I replaced the cracked original plinth guidance washers with a new Beolover Plinth Guide Washer Set for Beogram 4000, 4002, and 4004:

This shows one of them installed:

And here a shot of restored keypad together with installed plinth:

Beolovely! Now it was finally time to do all the adjustments. In these adjustments the arm travel across the platter needs to become parallel, the platter needs to be in the proper distance from the arms, and the platter needs to be flush with the surrounding aluminum panels. This can sometimes be a pretty iterative slog. Due to the little space the floating chassis has for movement there is not much room for 'improvisation' and everything needs to be perfect.

After this process was completed I did the arm adjustments. But first I replaced the flimsy locking washer that holds the counterweight screw in place

with a square nut and a washer:

The nut allows locking the calibration in place so it survives shipping.

Then I put a cartridge on the arm and calibrated the counterweight to get 1.2g at the 1.2g setting of the little tracking force dial:

The next step was adjusting the arm lowering limit that the needle would stop dropping about 1 mm above the lower platter rib sections:

This is an important adjustment in case the photocell in the sensor arm fails or another circuit malfunction occurs. The Beogram circuit only detects sensor lamp failures, which cause the arm lowering mechanism to be disabled.

Then I adjusted the tracking feedback

after which it was finally time to give this lovely Beogram a first test spin. I selected one of my favorite Herbie Hancock records, "Secrets" which was released in 1976 (CBS 34280). What a beautiful 1970s cover!...;-). A perfect contemporary to this Beogram, which may have been purchased in 1975 or 1976:

The Beogram played perfectly and so I started working on installing a new plexiglass dust cover. The first step was removing the badly scratched original cover from the metal hinge assembly. The mounting screws are easily accessed after lifting the aluminum trim strip on the sides with a razor blade:

I always epoxy small (grey) plastic bits into the strange channels they designed into the otherwise very nice replacement hoods from DKsoundparts in Denmark:

These channels make it impossible to bend the aluminum trip sharply down on the sides. Since there is a void under the strip in the channel area the bend invariable gets a bit rounded. The plastic bits make it easier to get a reasonably sharp bend across the entire width of the trim strip.

The next step was centering the new trim strip with my alignment tools

I usually use a piece of blue tape so I can make a pencil mark for the strip alignment:

Then I bolted the new hood to the hinge. I usually put a bit of white wood glue on the threads:

This helps keeping the screws in place. One should tighten them very much since this can easily lead to premature cracking of the plexiglass around the bolt holes.

The final step was glueing the new trim in place and bend it down at the sides: