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Monday, September 18, 2017

Beogram 8000: Testing The Restored Components

All of the key Beogram 8000 components have been examined and restoration work was performed where necessary. Now it is time to connect them up and see where things stand functionally. This is the most exciting time of the restoration (other than the first play of a record).

I plugged the Beogram into the AC power socket and started checking the main voltages. All were present and accounted for.

The red standby dot was lit on the display so I pressed Play and observed the Beogram come to life and search for a record to play.

The tangential arm assembly moves across the platter looking for a record. The lamp and sensor in the fixed arm send back a triangular signal when no record is on the platter.

Here is the detector arm circuit and measurement with my oscilloscope.

The signal looks just as expected and the Beogram correctly determined there was no record at both the 12 inch record and 7 inch record locations.

Another sensor voltage I check is really two signals that come from the tangential arm drive system. Two pulse signals from sensors reading the rotating arm drive screw, feed the Beogram sensor counter.

Here is that circuit and the measurements.

Both signals are working well. 

The next sensor to check is platter speed.  This is the sensor that reads the metal tach disk. The pulses feed the Beogram microcomputer where the speed is automatically adjusted to either 33 1/3 or 45 RPM.

Here is the circuit and measurements for both platter speeds.

As a reference I put the channel 2 scope probe on the microcomputer PCB 5 VDC power.  Everything looks great with the speed sensors. The Beogram immediately changes speeds and locks in to which ever speed is selected.

I can also report that the tangential arm assembly is moving easily and is very stable with the repaired arm drive bearing installed.

There is one more set of sensors I will measure and adjust tomorrow. Those are the two LDR sensors for forward and reverse scanning. I want to install my usual test connector for those so I can re-check those sensor voltages after these components are installed back in the Beogram cabinet.

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