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Thread: Scanner problem 6800HP

  1. #1
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    Default Scanner problem 6800HP

    Hello,

    I have a problem with a setup of 2 6800HP galvo's with Medialas microamps. In the video i drive the galvo's with a static targeted beam but both the galvo's react abnormal.
    Does anyone have a clue what might be the problem?
    Thank you for helping me out.

    https://youtu.be/YYPW_cXKgBE

    Kris
    Last edited by KrisVermeulen; 04-22-2021 at 10:47.

  2. #2
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    That is the symptom of a badly over-loaded power supply going into current limit and shutting down.

    Steve
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  3. #3
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    Quote Originally Posted by mixedgas View Post
    That is the symptom of a badly over-loaded power supply going into current limit and shutting down.

    Steve
    Thank you Steve.
    What could be the cause of this 'overload'?


    Bad Galvo's... (Both of them? - They are very old)
    Bad power supplies or bad connection?


    I find it strange that there is an overload possible when there is no motion asked (Static beam)


    Kris

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    Detach each scanner axis one at a time from the PSU. Ie...power up X axis only, then Y only. Let the scanner inputs float while testing by pulling to common PSU ground by 10 k to 100K Ohm resistor. Can also be insufficient size of PSU. Note Galvos have a huge surge on startup.

    Faults that I have seen do this:

    Bad galvo coil
    bad galvo internal position sensor,
    Bad Amplifier
    Bad PSU
    One Galvo shorted
    Galvo amp mistuned / potentiometers set wrong / galvo feedback signal missing / bad voltage regulator on one amplifier (amplifier slammed to one power rail causing overcurrent)
    PSU too small
    PSU not wired correctly on PSus with voltage sensing feedback terminals unconnected. Such terminals would be marked "Sense" or "S" and be right next to the output terminals.
    Bad wiring
    Positive PSU and Negative PSus not sharing common analog output ground.
    One PSU installed backwards.
    Undersized PSU
    PSU does not have enough load to turn on / oversized PSU (only on certain surplus psus)

    There are others.

    Pangolin has a scanner/projector wiring guide written by Bill Benner. . You should check your work against it.

    Steve
    Last edited by mixedgas; 04-23-2021 at 13:17.
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  5. #5
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    Thanks again Steve. Your help is really appreciated.

    Today i did some testing with mixed results.
    On the 6800HP set from above there is one galvo OK and the other galvo forces the PSU's into overload (not sure why).
    Then i noticed that this set contains 2 Y - galvo's (I didn't know there was a difference between X and Y galvo's).

    Luckily i have 2 other sets with 6800 galvo's.
    Then i tested all the galvo's. Seems that out of the 6 there is only one X-galvo OK and there are 2 Y-galvo's ok (not sure of it).
    When steering the Y-galvo's to there outer limits, there is only minimal movement, but they move.

    So there are 3 not ok. One is as said earlier forcing the PSU into overload. The other 2 are not moving at all.

    Wiring is as follows...
    Notice that the feedback signals from the microamps are not connected.
    I checked the document from Bill Benner and i think that the wiring is OK.

    Kris
    Click image for larger version. 

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