Some time ago, a customer in Texas purchased a Beogram 4000 turntable on eBay from a seller in New York. The turntable was in fair condition, as detailed on the blog (see hyperlink). To address a cracked corner on the dust cover, the decision was made to acquire a second Beogram 4000, allowing the creation of one flawless unit from the two. With the arrival of the second turntable, the restoration began.
The unit in superior cosmetic condition was chosen for the project. The initial focus was on reconditioning both the carriage transport system and the arm lowering mechanism. During shipping, a common issue with Beogram 4000s occurred – one of the carriage’s linear bearings became detached. These bearings, depicted as white triangles in the provided image, are essential for smooth carriage movement.
Concurrently, the threaded rod and polished shafts guiding the carriage were extracted, cleaned, and the remaining linear bearing, along with its threaded nut, underwent ultrasonic cleaning. To prevent future dislocation during shipping, a touch of epoxy was applied to the bearings before re-inserting them into the carriage.
Following the carriage’s restoration, attention shifted to the arm lowering mechanism. The mechanism was meticulously disassembled, cleaned, and reassembled. Afterward, the focus turned to the rear of the Beogram. The sensor arm, responsible for detecting the record’s grooves, required lubrication at the point where it connects with the damper.
After removing two screws securing the sensor arm, the linkage was detached. A small spring housed beneath the linkage’s circlip demanded careful attention during this step to avoid misplacement. With the pivot point cleaned and freshly lubricated, the sensor arm was returned to the carriage, followed by meticulous adjustment to ensure the arm’s parallelism.
The next phase involved upgrading the tracking sensor’s illumination. The original incandescent bulb was replaced with a modern LED equivalent. This modification enhances longevity and efficiency. Lastly, a cracked plastic pulley associated with the carriage motor was replaced with a precision-machined replica.
The restoration then transitioned to the Beogram’s electronics. The main PCB received significant attention, with electrolytic capacitors, the RPM relay, and RPM trimmers all being replaced. For enduring precision, new 25-turn potentiometers were installed, allowing easy access from the board’s soldered side. While a photograph wasn’t taken, two electrolytic capacitors on the power supply board were also replaced.
Next, the main reservoir and motor capacitors assembly underwent restoration. Over time, these capacitors commonly deviate from their specifications and necessitate replacement to ensure optimal performance. Disassembly revealed evidence of leakage, emphasizing the importance of this procedure.
Taking advantage of the situation, the AC motor was removed and disassembled. Its simple, robust design, featuring a synchronous “can motor” configuration with no brushes or commutators, was evident. To address potential knocking noises, a common characteristic of these motors, the enclosure and its embedded bearings were submerged in oil and subjected to a vacuum overnight.
The motor was then reassembled, utilizing 3D-printed components for securing M3 nuts, replacing the original threaded rivets. New capacitors were installed using a custom 3D-printed fixture for optimal placement.
The subsequent stage of the restoration concentrated on the Beogram 4000’s control center – the keypad cluster. This assembly, employing early TTL chips, represents a sophisticated hardwired digital logic system for its time. The vertical PCB houses the logic chips, while the keypad switches reside on a PCB behind the keypad’s surface.
Cleaning and gold-plating the switch terminals were paramount. Given their susceptibility to oxidation, these mechanical switches are critical for the turntable’s functionality. The terminals, exhibiting significant blackening, were gently restored using 1500-grit sandpaper and ultrasonic cleaning with detergent and isopropyl alcohol.
After cleaning, the terminals were nickel-plated to create a suitable surface for gold adhesion. Employing a wand-based plating method, a durable nickel layer was achieved in a matter of minutes. This was followed by gold plating, resulting in a resilient and conductive surface. The gold-plated terminals were then meticulously reinstalled onto the PCB.
Continuing with the keypad’s refurbishment, the four incandescent bulbs were replaced with LED equivalents, significantly extending their lifespan and efficiency. Before reassembly, a common issue was addressed: the strobe mirror had detached. This delicate component was carefully glued back into place, a procedure frequently necessary in Beogram 4000 restorations.
With the keypad nearly complete, the cracked plinth guidance washers were replaced with new 3D-printed versions. Notably, the front center washer was changed to black, preventing visibility through the gap between the aluminum panels and plinth. Next, the carriage switches, responsible for relaying the carriage’s position to the control system, were rebuilt.
The gold-plating process wasn’t finished yet. Attention shifted to additional switches located near the arm lowering solenoid. Evidence of prior tampering was apparent, with bent switches and missing mounting bolts. Restoring these switches proved intricate due to their vertical PCB mounting, soldered connections, and delicate wiring.
To access the terminals, the vertical boards were carefully unsoldered and removed. The terminals, including those for tracking enable, output grounding, and solenoid current reduction, were plated with gold. Finally, the restored terminals and switches were meticulously reassembled, ensuring long-term functionality and reliability.
Before returning the keypad to its enclosure, the last incandescent bulb, situated within the sensor arm, was replaced. Accessing this bulb required extracting the sensor compartment from the aluminum profile. Due to limited space, a custom flex PCB with an integrated LED and bypass resistor was used to maintain compatibility with the bulb failure detection circuit.
Moving on to the signal path, the existing plastic DIN5 connector, likely a subpar replacement from the past, was upgraded to a high-quality, all-metal connector with gold-plated pins. To address potential hum issues, a switch for connecting system and signal grounds was installed at the tonearm’s wiring terminals. This modification proves beneficial when using non-B&O amplifiers.
The final stage involved meticulous adjustments and alignment. The aluminum panels were meticulously aligned with the keypad by carefully bending alignment pins. Next, the sub-chassis and platter were leveled and adjusted to ensure free movement within the enclosure. The tonearm’s horizontality and distance from the platter were meticulously calibrated.
As a safety measure, the arm lowering limit was set to approximately 1mm above the platter’s lower ribs. This precaution prevents potential cartridge damage should the record detection system malfunction. The tracking weight adjustment was then calibrated.
To ensure lasting precision, the counterweight’s locking mechanism was enhanced. The fragile circlip on the adjustment screw was replaced with a more robust M3 nut and washer. Using a digital tracking weight gauge, the spring-loaded weight adjustment wheel was calibrated for accuracy.
The final electrical adjustments involved calibrating slow carriage speeds, RPM, and motor voltage. The motor driver signals for 33 and 45 RPM were fine-tuned using an oscilloscope. The end groove detection circuit was then adjusted to ensure proper activation at the record’s end. This involved setting a voltage threshold that prevents premature arm lifting during normal playback. Lastly, the tracking feedback was optimized, made significantly easier by the adjustable intensity of the LED tracking sensor light source.
Finally, with all restorations and adjustments complete, the Beogram 4000 underwent its inaugural test run. A meticulously cleaned record was selected, and the turntable performed flawlessly, bringing the joy of vinyl back to life. The only remaining task was restoring the dust cover – a project for another day.