Beogram 4002 (5503): Restoration of the Carriage Position Sensor - Development of a New Beolover Part

The Beogram 4002 (5503) that I am currently restoring had a damaged carriage position sensor photo resistor housing, which had broken off mounting tabs:

I removed the photo resistor housing:

This shows it from the back:

After pulling out the bottom part, the photo resistor can be extracted:

I designed a replacement housing that I can print on a 3D printer. It consists of two parts. This shows them together with the extracted photo resistor:

This shows how to integrate the photo sensor with the assembly:

First straighten the leads of the photo sensor and put it on the insert part like this:

Then slide the main housing over the insert with the photo resistor:

This shows the assembled sensor from the bottom:

Now the assembly can be inserted into the original mounting cutouts:

Once the sensor has been clicked into the PCB, the leads can be soldered to the pads:

I decided to also replace the position sensor light bulb with an LED. This shows the original lightbulb lit up in its housing:

Removal of the housing reveals the light bulb soldered to its two pads:

The right pad is the 24V rail, while the left pad connects to GND via 1R91. It is easy to replace the bulb with a LED: Basically any LED will do. I selected an amber LED with a 2.1cd light output at 20mA that I had in my stash. Since it runs from 24V in this setup, a resistor needs to be put in series to limit the current. I selected a 3.3kOhm resistor that limits the current to about 7mA. This current lights the LED up in a low key way, similar to the output of the light bulb:

This shows the entire restored carriage PCB (I also replaced the 47u electrolytic capacitor and the 8.2 Ohm solenoid resistor):

After I installed the carriage again I tested the sensor output by measuring the collector voltage at TR23, which should give clean 24V signals every time a black segment of the 'plexiglass ruler' gets pulled between the LED and the photo resistor. This shows the signal that the 45 RPM pattern caused, while the carriage swept the platter:

This looks like it should, i.e. we can conclude that the restoration of the carriage position sensor was successful.