Beogram 8002 arm moves 1″ then returns to stop

[sonavor]

The Beogram 800x turntables rely on the position sensors that the spindle pulley assembly passes across.  When you press Play the Beogram circuity drives the spindle forward until the mechanical SO switch disengages.  At that point the Beogram uC begins counting the position sensor generated pulses to keep track of where the arm is.

It sounds like your position sensor assembly is either failed or the path from the sensors to the circuitry on PCB1 and PCB2 is broken.

-sonavor

[TomIM]

Thanks for the information sonavor. Is the board with the 3 components a photo interruptor

and if I want to check it can I use a voltmeter or scope and see DC voltages or pulses? Is this turntable designed for the arm motor to stop if no pulses are going back to the micro, because the arm doesn’t go far enough for the mechanical switch to disengage before it stops.

Thanks, Tom

[sonavor]

Yes, there is one emitter and two receiver/sensors.
They are shown on the service manual schematic (1-2).

You should be able to see the activity on an oscilloscope.
However, since you don’t clear the SO switch I would suspect a problem with the control for the Servo motor.  You mentioned that you found quite a few bad wires already.
I suggest you start looking at Motor Control part of the schematic.
Also check the “>>” and “<<” LDR adjustment per the service manual.
Their steady state adjustment affects the Servo Motor control.

-sonavor

[Dillen]

The return to stop indicates a CPU reset.
Replace capacitors, replace CPU socket, check solder joints.

Martin

[TomIM]

Thanks sonavor and Dillen for the information. I have to put this on the back burner for now as I’m getting behind in other work. I’ll check out the things you suggested and follow up with reports of success or other questions. Tom

[Author]

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