Rabco SL8E Photoelectric Servo Control Retrofit

[Rajkumar_]

Hello after photoelectric servo modification on my Rabco SL8E with led (same nero52) I have notice led turn on & off very few seconds, it’s correct.? Or led continuously turned on? Thanks Rajkumar

[diyrayk]

The LED circuit itself is probably working correctly. The ideal is for the motor to operate continuously, and speed up or slow down as the groove pitch varies. You can verify this most easily by monitoring motor voltage directly with an analog voltmeter. With a theoretically constant groove pitch, the motor voltage will also be constant. Groove pitch in the real world is not constant and records are also off-center to some extent, so motor voltage isn't constant but varies up and down with each revolution. LED's like to be either on or off. My guess is that the LED circuit is biased somewhere in the middle of the motor's actual operating voltage range and is turning on and off as the motor swings within that zone. The LED turn-on point could be manipulated by selecting the gain of the added transistor and the value of the added 4K7 resistor.

I deliberately did not include an LED indicator on my arm partly out of laziness but more out of the philosophy that, if I can't hear the effects of the servo in action, I don't want any visual cues that it's operating. I leave my test equipment connected for as long as I need to see what the servo is doing while setting it up but once that's done I prefer to fly/listen 'blindfolded'.

Ray K

[Rajkumar_]

Rayk absolutely you correct, I have check many LP's many of then off center this is the reason led light (motor) turn on/off, one of the my LP I found correct center than led turn on continuously. Now I have cleared my doubt. I have installed 2 led red & green. Green for carriage and red for lifting. Everything working perfectly. I have post some pictures. Tks lot Rajkumar.