Beogram 8000: Workshop Test Unit

Recently a couple of Beogram 8000 owners sent me their circuit boards for evaluation. They are DIY type owners that needed some help with the electronics area of the restoration. It is much easier to work on the electronics portion of a restoration when you have good, working units to compare to.

This is the case with my Workshop Beogram 8000 turntable.

The parts shown above have gone through my typical Beogram 8000 restoration steps.
Everything on this turntable is fully working but will remain (for now) outside of its cabinet.
With everything open and accessible I can easily swap parts and connect measurement equipment to signals I need to measure.

For the main board I have now added the main Beogram 8000 signals I like to check: position sensors, tracking sensor, speed sensor, record detection sensor and the two servo motor control lines (forward and reverse).

I also recorded some measurements of those signals for key operations of the Beogram.

This picture shows the oscilloscope measurement when the Beogram 8000 Play button is pressed and there is no record on the platter.
For this mode of operation I looked at the two position sensors (of the tangential arm movement), the platter speed sensor and the arm detection sensor.

The activity begins as the platter starts to turn and the tonearm assembly moves towards the platter to search for a record to play.

Pulses on the Record Detect Sensor indicate the platter is empty.  
The pulses on the speed sensor show the turntable locked in at 33.33 RPM.

The two position sensor signals show a constant speed during the scanning for a record.

Those signals are as expected and indicate a healthy working Beogram 8000.

Here are some oscilloscope signals of the Beogram starting record play of a record on the platter.
I swapped out the Record Detection Sensor signal with the Servo Motor Forward signal.

The Position Sensor 2 signal was swapped out with the Beogram 8000 Tracking Sensor.
The Platter Speed Sensor signal was swapped with the Servo Motor Reverse signal.

The first picture shows the activity after Play is pressed to where the tonearm sets down on the record and accelerates through the lead-in groove.
Note the slow down of the servo motor right before the set down point.

Here is a picture of the activity during typical record play.
You can see how activity on the Tracking Sensor relates to forward movement on the Servo Motor Forward signal.

This last oscilloscope picture shows those same signals at the end of a record when the Beogram 8000 reaches the run-out groove of the record and the end-stop logic instructs the Beogram to stop play and fast scan in reverse back home.

With this tested and working Beogram 8000 I will now swap out some problem electronic parts and trouble-shoot their issues.