The last remaining bulb to be replaced with an LED in this Beogram 4000 was the one in the sensor arm. A new flexPCB assembly with a warm-white LED was designed to fit within the sensor arm’s bulb compartment. This particular Beogram 4000 model has a sensor arm with a socket connection for the bulb/sensor compartment. This convenient design allowed for simple removal of the entire assembly, making the LED conversion a benchtop task.

Here, you can see the LED assembly alongside the removed bulb compartment:

And here it is with the LED installed:

The 3D-printed red wedge ensures the LED sits precisely where the filament of the original bulb was located. Before installation and testing, the voltage at the collector of TR14 was checked. TR14 amplifies the sensor signal before it enters the record detection circuit. In the Beogram 4000, a voltage of 2.2V DC at the collector signifies no sensor signal, which was confirmed in this case:

With this confirmation, the installation proceeded:

The warm-white LED emits enough red light to illuminate the B&O logo in its original color. As a final check, the sensor’s response was measured with no record on the platter. This measurement, also taken at the collector of TR14, should be 2.2V with the sensor positioned over the spinning platter. This ensures the arm lowering circuit is properly deactivated when no record is detected:

This Beogram 4000 passed the test flawlessly, with each dip in the graph representing a platter rib passing beneath the sensor. A real-world test, both with and without a record, confirmed the circuit’s functionality.