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Thread: fb3 odd output query

  1. #1
    Join Date
    Nov 2019
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    2

    Default fb3 odd output query

    hi new to this so hope i got the right place.
    i have quickshow and a chinese rgb analog laser, it all works ok. But occasionally the Y axis scanner goes a bit crasy. i checked all the wiring seems fine, also measured the output voltages from the fb3 and thats where i find something i didnt expect.according to the ilda specificatins i can find online the x and y signals are made up of two +5v to -5v differential signals. fine so id expect to see +5 to -5 on the x+ signal and the same on the x- signal which i do no problem, however on the y side its very different. I see 0v all the time on the y+ lead and 0 to -10v on the y- lead. odd. anybody know why the Y signal format is different to x signal? i was expecting them to both be the same. I am testing using beam targets setup for each corner of the display. so i can see max x max y, min x min y in each position. the x channel is perfectly ok just the y is odd, doesn't seem ilda standard could this be a problem?

  2. #2
    Join Date
    Feb 2008
    Location
    East Sussex, England
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    5,212

    Default

    What do you mean by "a bit crazy"?

    If the image goes all wild and you have to power cycle the projector to reset it then it sounds like you may be scanning too fast/wide and popping the poly switch on the scanner amp.
    Power cycling the projector resets this.

    But it could be that the poly switch is a symptom of the FB3 output issue.

    It's also worth noting that some cheap chinese lasers only use scanners with single ended inputs anyway.

    Also, where are you measuring the signal, directly from the FB3, or from somewhere in the projector?
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  3. #3
    Join Date
    Nov 2019
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    2

    Default

    thanks for reply, by a bit crasy i mean it starts to flyback and jump around and not blank the beam but only in top corner of the display , max x and max y values everywhere else is fine. thats why i measured the voltage s. im measuring them at the fb3 with no load, i only have a dmm no scope unfortunately. its like maybe something is overloading in the scanner and i wanted to check the input was ok.

  4. #4
    Join Date
    Mar 2013
    Location
    Langhus - Norway
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    330

    Default

    Quote Originally Posted by eboy View Post
    thanks for reply, by a bit crasy i mean it starts to flyback and jump around and not blank the beam but only in top corner of the display , max x and max y values everywhere else is fine. thats why i measured the voltage s. im measuring them at the fb3 with no load, i only have a dmm no scope unfortunately. its like maybe something is overloading in the scanner and i wanted to check the input was ok.
    Try swapping the input on the X and Y to see if the issue moves along to the other scanner. If so, it might be an issue with the FB.
    From your description, I lean towards an issue that triggers the polyswitch.

    Espen
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  5. #5
    Join Date
    Jan 2006
    Location
    Charleston, SC
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    2,147,488,814

    Smile

    Just for the record, a digital multi-meter is not going to give you an accurate reading of the voltage on the X and Y output pins of the Quickshow controller because those signals are constantly changing in time. (It's an analog signal with a varying time period that changes based on your points-per-second setting and the frame-rate, which in turn is governed by how many points are in each frame you display.)

    Even when set to "AC" mode, a DMM will only give an approximation of the real output, and in most cases that approximation will be *way* off because the DMM is expecting a constant 60 hz (or 50hz in Europe), while the controller output signal will almost never be near that frequency (and will often be an order of magnitude higher, if not more).

    Bottom line: you *need* an oscilloscope to measure the output voltage of a laser controller accurately.

    Despite all that, the symptoms you are describing do not make me think there is a problem with your Quickshow controller. As mentioned above, I would start your troubleshooting at the projector end.

    Adam

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