I’m currently restoring an early model Beogram 4002 (5501) turntable, and it’s captivating to trace the evolution of its design from the original Beogram 4000. Having already tackled the arm lowering mechanism, I’ve shifted my focus to the carriage position switches, a particularly interesting aspect of the 4002’s design.

While the design echoes that of the 4000, it features some notable refinements. The 4000’s 7" record set-down point switch, for instance, was a break switch prone to issues stemming from oxidation. This vulnerability arose because the switch’s initial contact relied on the spring force of the contact terminal. Even slight oxidation could lead to a permanently open switch, significantly disrupting the entire control system and often causing the arm to drop immediately upon powering on.

This potential problem was addressed in the design I’m currently working with. The 7" detection now employs a standard make switch.

Nevertheless, these switches remain the most likely culprits for issues in these units. Therefore, it’s generally advisable to gold plate all their spring terminals to prevent oxidation and substantially reduce the chance of future control system problems. In this particular 4002, the switch actuators were also immobilized due to hardened lubricants. Consequently, I disassembled the components, lubricated the actuators, and gold plated the terminals. Here are some observations from this process:

The image below displays the switches after removing the plate holding the springs that depress them:

As you can see, the rightmost switch is stuck in the down position.

Given that the 550x models were manufactured before board-to-board connectors were widely adopted in consumer electronics, accessing the switches and the plastic tabs securing the actuator assemblies to the PCB requires carefully flipping the board upward. This maneuver necessitates moving the aluminum profile on the left out of the way, which can be achieved by removing the two screws holding it in place.

The following image shows the board after the profile has been removed:

After desoldering the leads of the carriage motor and the end groove detection sensor, I lifted the board and removed the actuators:

Next, I removed the contact terminals (following this order is crucial to avoid damaging the transparent plastic parts with the desoldering gun):

After cleaning the terminals with a fiberglass pen, I applied a gold coating:

The result is a beautifully polished finish!

With that done, it was time to reassemble everything. I started by soldering the tabs back in:

These need to sit flush against the PCB. Then, I lubricated the red actuators and carefully inserted their tabs back through the PCB (applying a small amount of grease to each tab helps reduce the required force and minimizes the risk of breaking the delicate tabs).

This image shows everything back in its proper place:

All the switches are now in the up position and move freely. I attempted a test run of the turntable, but encountered some significant operational issues. The carriage motor runs only briefly after startup, and the tracking sensor LED flickers during this time. This suggests serious power supply problems, which will be the subject of my next post!