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Thread: Galvo connector pinout?

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    Default Galvo connector pinout?

    Hi,

    I got some galvos but don't have any technical details for them. This is the connector:





    I also took a look into the galvo itself to perhaps see where the feedback diodes may be connected, but there are none:



    So does anybody have some ideas about the pinout of this galvo or how to find out what may have to be connected where at this plug?

    Thanks :-)
    Attached Thumbnails Attached Thumbnails IMG_20200912_174638.jpg  


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    A picture or two of the full galvo body will help, as well.
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    Quote Originally Posted by absolom7691 View Post
    A picture or two of the full galvo body will help, as well.
    There it is:


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    Drive coil is 4 wires:
    Attached Thumbnails Attached Thumbnails DRIVE COIL.png  

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    OK, you have a capacitive position sensor. But it looks like a very simplified copy of something I have seen often.
    ~
    This is an educated guess from studying the picture.
    ~
    See if the wires are marked AGC, A, B, I see GC under the yellow signal lead.
    ~
    IF so AGC is the oscillator bias for gain control or in some cases oscillator circuit power, one way or another the Galvo amplifier regulates that voltage and probably limits its current.
    ~
    A, and B would be the position signal, which is usually a tiny current output, , not a voltage. That differential current signal will ride on a ton of RF noise, requiring a different style of Galvo amp designed with LC filters in the input.
    ~
    Terminal marked GND will Ohm out to one of the signal leads.
    ~
    Do NOT try to meter or scope any of the leads from the sensor drive transformer with the power on, voltages can be on the order of 300VAC at a Megahertz or so.
    ~
    DO NOT UNSCREW OR REMOVE THE BOARD!!!!!! There are very tiny wires on the back side that WILL break.
    ~
    I have no idea who made that.... Nor how to bias / power the sensor.

    ~
    As most people on this board have never dealt with a capacitive sensor with the lid off, expect little help. Its not a traditionally G120 style sensor, probably more modern like a clone of an M3. But it has AGC, so it comes from the "Boston" origin
    ~
    Attached Thumbnails Attached Thumbnails wierd galvo ANNOTATION 2.jpg  

    Last edited by mixedgas; 09-14-2020 at 07:13.
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    See attached

    I am not saying a CX-660 would drive that unknown Galvo. But it is where I would start. I would not connect the drive coil until I was certain the position sensor was working perfectly on an oscilloscope and I had followed the calibration instructions. . Usually this is done by lifting/removing the amplifier output fuse.
    ~
    The other schematic would give you a start on a demodulator, but again, a long shot. I erased the output stage chip as it is A. Obsolete Custom Un-obtainium , B. Friends don't Let Friends Build Disasters That Kill Galvos.
    ~
    I hope this is just a learning project for you. Ask yourself, is all this work too much for a slow 10 Kpps Galvo set? This is 1990s technology. Capacitive sensor galvos don't work with amps designed for optical sensors, although the rest of the circuit is nearly identical, the position sensor input circuit is NOT.
    ~
    Steve
    Attached Thumbnails Attached Thumbnails simple g120.gif  

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    Last edited by mixedgas; 09-14-2020 at 07:35.
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    Great, that really helped me a lot!

    red/black and white/yellow from one cable indeed are directly connected to the galvo coils, I measure 1,5 ohm there and can move them when applying 1,5 V (they're moving to their limit, so the nominal maximum voltage seems to be less).

    From the other cable the black wire seems to be ground while the yellow one indeed is AGC - I found that printed on the board when removing the cables carefully from the housing. The white wire is named as "B" and the red one as "R" on the board, so that seem to be the feedback-wires you mentioned.

    Btw.: this is for learning and playing around with the technology only, so the time I invest here does not matter :-)
    Last edited by Elmi; 09-15-2020 at 01:53.

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    See attached for current limited , capacitive feedback, AGC power circuits.

    You could load them into LT-Spice and see what they do...

    These are snipped from the two documents I attached earlier.

    1.2 Ohms indicates a more modern coil design, traditional coils were on the order of 7 ohms. If you buy a CX-660 on Ebay for next to nothing, consider adding 2 Ohms, 10 watts, in series with the coil.



    Steve
    Attached Thumbnails Attached Thumbnails ELMI AGC.png  

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    Quote Originally Posted by Elmi View Post
    Great, that really helped me a lot!

    red/black and white/yellow from one cable indeed are directly connected to the galvo coils, I measure 1,5 ohm there and can move them when applying 1,5 V (they're moving to their limit, so the nominal maximum voltage seems to be less).

    From the other cable the black wire seems to be ground while the yellow one indeed is AGC - I found that printed on the board when removing the cables carefully from the housing. The white wire is named as "B" and the red one as "R" on the board, so that seem to be the feedback-wires you mentioned.

    Btw.: this is for learning and playing around with the technology only, so the time I invest here does not matter :-)
    Take a look on the patent server for US Patents assigned to General Scanning, with inventor Brosens, Montagu, Dowd, Rohr, Stokes, Brown etc..
    You'll find enough drawings to start figuring out what is on the other side of the board, be it a shaped rotor as the feedback capacitor "blades" or a "Butterfly" soldered onto the rotor as the feedback element.

    4135119 gets you the G120 frame and rotor. 5099386 Gets you a drawing based on a GS M3.0 9938622
    UK 2279460 Gets you an advanced concept circuit.
    ~
    Note patents are examples of a concept, rarely are the circuits shown copied from production drawings. Usually they have an error or two designed to throw off copying.
    ~
    If you look at drawing 3A in the UK patent, you can see why you need external current limiting on the OSC PWR / AGC input. The transformer inductance will limit the current flow somewhat, but probably not enough. I'd start with a 470 Ohm resistor. a 1000 Ohm resistor, or a 20 mA led constant current limiter IC chip if I had nothing else. 12V/470 = 25 mA.... Which is about all I'd ever put into a sensor when starting out. A Microchip CL1 is an example of a current limiter IC.
    ~
    Most two channel Oscilloscopes have a Channel One Minus Channel Two Function, or a Channel Sum mode. By putting a 1K load resistor on the sensor outputs and looking at the millivolt signals with a scope, you will probably see a tiny signal riding on a big DC offset with much RF noise as you move the galvo shaft with your gloved fingers. Most sensors put out differential signals for noise immunity reasons. Hence using both channels of the Oscilloscope to cancel the common mode noise from the sensor.
    ~
    DO NOT TRY TO ROTATE THE SHAFT MORE THEN SAY 40 DEGREES on a GSI PRODUCT OR COPY.
    ~
    OK, That is probably all I can do to help you... Pay the 1.00$ for Bill Benner's Galvo Book on line.

    Steve
    Last edited by mixedgas; 09-15-2020 at 07:50.
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