Beogram 8002 arm moves 1″ then returns to stop

[TomIM]

Hello: I have worked on other linear tracking turntables but not this one. The original problem was the arm went to the start of the reord but the tonearm didn’t lower to the record.

I cleaned the selenoid and then that was ok but when it reached the end of the record the arm just stayed there and didn’t return to stop. At one point the arm wouldn’t lower again and when I moved the wire harness it started working again. I then discovered a lot of bad solder connections with the 4 plug in cables, so I soldered them. I still had the problem with not returning at the end of record. Without doing anything else it developed a problem of the arm starting to move when play was started then returning to stop. The next attempt to play would work. After a few more times it would just go about an inch then return to stop. If you select play then use the left arrow the arm moves but when you select play the arm dips down slightly then returns to stop. I’m not quite sure where to start with this. I have a service manual but there are no troubleshooting flow charts. Any help would be appreciated. Thank you, Tom

[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]

Posts