Beogram 4004 Type 5526: Finalizing the Fixed Arm Record Detection

In the last post comments I mentioned learning something new every time I work on these Beogram turntables. This is certainly one of those cases. I installed the Beolover LED module in the fixed arm sensor assembly that I had swapped with a spare Beogram 4004 turntable. That sensor measured exactly as I wanted using the original incandescent lamp so this new LED light source should work just as well. To my surprise the LED light source produced a weaker sensor signal than the incandescent lamp. The signal was better than with the original sensor assembly but it still wasn't at the level I need it to be in order to continue with this restoration.

The peak-to-peak voltage target is 6 V and the above signal is still short.

Even though the LED light source looks brighter than the incandescent bulb there are other factors involved like the angle of the light on the spot that the sensor is focused on and the wavelength of the light. I discussed this with Beolover and determined that I needed to adjust the LED position on the Beolover light source.

Here is the Beolover LED module. The blue arrow shows the direction I am moving the surface mounted LED. How convenient that Beolover designed the solder pads for mounting the LED so that its position can be adjusted.

That was all it needed. The new position of the light source provides the necessary light stimulus to the sensor where it can now produce a healthy 6 V peak-to-peak record detection signal.

I am now confident in this circuit so I can continue on to the Beogram 4004's platter height adjustments.