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Thread: Troubleshooting/improving galvo respose

  1. #11
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    Well the pots are pretty accessible, but there's no labeling I can see. Going to send some mail to Goldenstar and hopefully get back which is which.

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  2. #12
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    Welp, I may be fairly out of luck here. I got a very quick, but unhelpful response from Goldenstar saying:

    We don't have it. I ask engineer he say may be need change the scanner.
    to my ask if they had any datasheets or similar with the pots labeled. I find that a bit hard to believe... but whatever I guess.

  3. #13
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    I find it difficult to believe that Goldenstar does not have the manual for the scanner amps. Sounds like the person who answered your email did not understand the question. (Not uncommon...)

    You mentioned that you bought the projector before the pandemic, so I suppose it's possible that the scanners are now obsolete. But at the very least, they should still be able to tell you what brand and model of scanners were used.

    Did you look closely at the circuit board, especially in the area immediately below the potentiometers? Sometimes you'll find abbreviated labels for each pot on the board itself. (SG, LD, HD, LN, PS, IS, etc)

    The other option is to look at the rest of the board, and also on the back of the galvos, to see if you can figure out what type of scanners you have. If you can figure out what sort of scanners are installed in your unit, you'll have a better chance of finding a diagram that has the pots labeled.

    The amp looks suspiciously similar to the DT-40 pro design. (That is, the newer version that uses a single amp for both scanners.) But your pots are all clustered together, while the DT-40 Pro mono-amp board has them separated. However, I know that Dragon Tiger went through several re-designs before settling on their current version of the mono-amp board, so maybe you have one of the earlier revisions? If that is the case, then you should see "DT-40 Pro" silkscreened on the board someplace, and/or on the backs of the position detectors on the scanners.

    Worst case, bring it to SELEM and we'll have a look in person!

    Adam

  4. #14
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    Quote Originally Posted by buffo View Post
    Did you look closely at the circuit board, especially in the area immediately below the potentiometers? Sometimes you'll find abbreviated labels for each pot on the board itself. (SG, LD, HD, LN, PS, IS, etc)
    Yeah, I did try and check - the board is very dense with a lot of SMT components, and there isn't anything that's clearly visible. There does appear to be some silkscreened letters *underneath* the pots, but nothing that looks like the abbreviations you mentioned. All I can really make out is "K" on each of them, so I'm pretty sure it's just the component number. I don't really want to take everything apart and desolder one to check.

    The other option is to look at the rest of the board, and also on the back of the galvos, to see if you can figure out what type of scanners you have. If you can figure out what sort of scanners are installed in your unit, you'll have a better chance of finding a diagram that has the pots labeled.
    I was able to find what I think are the part numbers:

    Amp: PH-6825THS
    Scanners: PH6830TH (these are pretty clearly labeled)

    Unfortunately, searching these gives pretty much no results. One of the only results is actually someone else in my shoes here. Their amp looks similar, but in a dual configuration like you mention. The vendor they referenced leads to an ebay seller that no longer seems to be active.

    Worst case, bring it to SELEM and we'll have a look in person!
    Bit far for me from Seattle unfortunately! Thanks for all the help. I've got another email out to Goldenstar, but I'm not super hopeful. I may be in the market for a proper one here soon.

  5. #15
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    Quote Originally Posted by Shasta View Post
    There does appear to be some silkscreened letters *underneath* the pots, but nothing that looks like the abbreviations you mentioned. All I can really make out is "K" on each of them, so I'm pretty sure it's just the component number.
    Agreed. No need to start de-soldering components!

    I was able to find what I think are the part numbers:

    Amp: PH-6825THS
    Scanners: PH6830TH (these are pretty clearly labeled)

    Unfortunately, searching these gives pretty much no results.
    Yeah, I couldn't find anything either.

    The crazy thing is that I've seen a set of these galvos before in another Goldenstar projector. It was around 2017-ish, and at the time I think the projector was less than a year old. I don't have any info on the tuning pots though.

    Can't believe no one at Goldenstar has any info on them though... That's just nuts.

    If all else fails, you can try tweaking each pot systematically to see if you can identify the low frequency damping, high frequency damping, and servo gain pots. Basically you turn a pot clockwise 1/2 turn and watch the test pattern, then turn it back 1/2 turn counter-clockwise (so it's back where it started), then go another 1/2 turn counter-clockwise and look at the pattern, and finally go back 1/2 turn clockwise so you're back where you started. Do that for each pot in turn. (All on one side, so you're only messing with either the X or Y axis.)

    The standard convention is clockwise = more, counter-clockwise = less. So as you turn each pot clockwise, you should be adding more of that particular adjustment. (In rare cases this is reversed, however, so take notes...)

    The servo gain pot will make the center circle get larger in one axis (so it becomes more of an elliptical shape). It will also cause overshoot at the corners of the center square on whatever axis you're on.
    The low frequency damping pot will reduce the overshoot at the corners of the center square. It will also have a small effect on the circle (making it slightly smaller).
    The high frequency damping pot will reduce the undershoot at the corners of the center square. It will have an even smaller effect on the circle (making it a tiny bit smaller).

    The input scale / image size pot will make EVERYTHING bigger (including the outside square of the pattern). Don't mess with this one - just put it back where it was originally set.
    The offset pot will move the entire image up or down (or left / right). Again, don't mess with it - just put it back where it was originally set.
    The linearity pot is where you can really get into trouble. It will appear to do almost nothing at first, but it will start to cause distortion the more you adjust it. Put this back where it was originally set and don't touch it again.

    If you can correctly identify the pots on one axis (or at least the 3 that you need), then you should be able to do the same for the other axis. (They will either be in an identical layout, or a mirror image, for the other axis.)

    Worst case, if you can't figure the pots out, you can always drop in a set of replacement galvos. (DT-40's are like $250 per set.)

    Adam

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