Beogram 4004 (5526): Replacement of Sensor Arm Bulb with a LED

After restoring the record detection circuit and the PCBs it was decided that the sensor arm light bulb should also be replaced with a LED to ensure operability of the deck down the road. These old light bulb like to fail, especially during shipping, i.e. it is a good idea to replace the bulbs with LEDs when restoring a Beogram. This shows the original light bulb in the sensor compartment together with the replacement flexPCB-based LED assembly:

I removed the bulb and inserted the LED board, which folds snugly into the compartment:

This shows the LED in action:

The LED is a warm-white type, i.e. there are enough red photons to ensure a properly colored B&O logo.

Whenever the light source in the sensor arm is replaced, the sensor response needs to be checked. The signal strength is highly dependent on the location of the light source in the compartment. The signal at the collector of the signal amplifying transistor TR3 needs to be close to 6V or better. This shows the measurement I made after the installation:

This Beogram record detection circuit is now operating better than spec (7.9V amplitude), i.e. we can confidently press the START button.