It is time to wrap up testing with the Workshop Beogram 8000 for now.
The test platform has helped me restore and repair five sets of Beogram 8000 circuit boards along with using the quick connect/disconnect socket on five uC (2IC1) devices.
The Workshop Beogram also gave me a way to test the speed sensor (OPE2).
I discovered that I had two faulty speed sensor devices in my collection of Beogram 8000 parts so this last Workshop Beogram 8000 blog post will show the result of my search for a speed sensor replacement device.
The original two types of speed sensor (OPE2) devices in the Beogram 8000 are these two Bang & Olufsen part numbers - 8330007 (the early type sensor with resistors R46 & R47 on PCB 1) and 8005067 (the later type sensor with resistors R2 & R3 on the speed sensor assembly).
I don't know the story with those part numbers but the 8005067 assembly is what is called out in the later model Beogram 800x turntables (BG8000 & BG8002). Maybe B&O had reserved that OPE2 part number but didn't release it until later.
Both sensor devices were similar slot type optical switches. They consist of an emitter that is an IR LED light source and an NPN photo transistor sensor. They are a single assembly with four leads.
Here are the two types of Beogram 8000 speed sensor assemblies.
Here are the wiring diagrams for both speed sensor assembly types.
I was unable to find data sheets for either type of speed sensor that B&O used for these two types of slot type optical sensors.
Electrically I run the wires from the speed sensor I am testing to a breadboard setup to measure the slot optical sensor output (with an oscilloscope). The breadboard contains necessary current limiting resistors (R46/R47 or R2/R3). I use a bench power supply to provide the +15 VDC power for the circuit.
Because this is an 8330007 B&O speed sensor I am using current limiting resistors per the schematic. It also matches what was installed on the PCB 1 board for this type of sensor assembly.
Applying the +15 VDC power to this circuit and manually rotating the platter hub here is the oscilloscope measurement.
The amount of current this sensor circuit draws with the +15 VDC power applied is 30mA.
The second test setup is with a B&O 8005067 speed sensor assembly. It has built in current limiting resistors (R2 and R3).
Since the 8005067 speed sensor assembly has current limiting resistors built into the assembly it isn't necessary to connect up the test components on the bread board like the 8330007 speed sensor. I can just connect my scope probe and DC power supply directly to the sensor assembly.
Just like the first sensor, the 8330007, this 8005067 sensor is also a fully working unit that I tested with the Workshop Beogram 8000 turntable.
The device I chose for this test is the TT Electronics/Optek Technology OPB370N55.
Here is the test setup with that device. It will require the use of the breadboard to provide the current limiting resistors.
To get a usable signal from this new sensor device I had to adjust the trimmers to around 2.4KΩ for R46 and around 6.8KΩ for R47.
Using those values I get a good, healthy speed sensor signal that uses about 10mA with the +15 VDC power applied. That is half the amount of current used by the 8005067 devices and a third of the amount of current used by the 8330007 devices.
Now that I can see what values I need for the two current limiting resistors I can try out this replacement sensor device in a failed 8005067 speed sensor assembly and test it with the Workbench Beogram 8000 turntable.
I am using the 8005067 assembly for the test and I am using 2.2KΩ for R2 and 6.8KΩ for R3.
That looks perfect. The raw signal off the OPB370N55 collector is a nice strong signal that feeds the 1IC1 Op-amp before being routed up to the uC pin 40 input (via the signal conditioning flip-flop).
My final check is to connect up the new speed sensor to the Beogram 8000 P4 harness normally and see how it works under full control of the Beogram 8000.
For this test I utilized the Beogram 8000 "Turn" function button.
The signal at the uC pin 40 still looks great and the Beogram 8000 control circuitry has no problem locking in the platter speed.
It looks to me like the TT Electronics/Optek Technology OPB370N55 Slotted Optical Switch is a good replacement for the Beogram 8000 speed sensor device.
If you try it keep in mind that you must change the resistors (either 1R46 & 1R47 or R2 & R3) according to the version your Beogram uses.
There are two other Slotted Optical Switch devices by TT Electronics/Optek Technology that I will try.
I will be retooling my workbenches to begin some restoration work on some Beomaster 4400 units next.