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Thread: New pt-40k galvos acting weird

  1. #1
    Join Date
    Dec 2009
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    Default New pt-40k galvos acting weird

    so i put together my new galvo setup.
    And it plays images perfectly!
    But then after some time sometimes instant others take about a min the image goes crazy
    http://s755.photobucket.com/albums/x...1006053053.mp4
    i Have no idea why its doing this.
    I am running a c-media audio card with an audiolase DAC connected to a show card then to galvos.
    the comp has run shows before just fine, but these new galvos are not working out.
    Maybe an overheat.
    But on what. its secured to a 1/2in aluminum plate.
    I hope i dont have to go and re solder or send these back...
    Maybe its a problem of running threw the show card?

  2. #2
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    It looks like both X and Y axis go at the same time, so it will be something common to both. Is it the PSU? Can you measure the rails before and during this strange behavior?

    Can you post just a static image like the ILDA test pattern to be sure?
    This space for rent.

  3. #3
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    i will be able to check that as soon as i awake.
    I have not slept been working on this all night.
    So lets just say for the sake of argument the psu is bad.
    i have a psu from my 20ks and i have a few pc psus.
    is there any way i can get one of those to fill in?
    btw i was able to run alot longer if i turned scan angle down.
    but i had to turn it down a good 65%.
    the psu reads +24 and -24
    darn was hoping my pc psu of =12 and - 12 might be able to do it...
    im thinking it may be psu as i doubt both scanners would die at the same time just not getting the power.
    Now to find a way to test.

  4. #4
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    Sep 2011
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    I had the same thing happen to mine. There's a ceramic cap-looking orange thermal fuse in-line with the main fuse. Once it overheats, it's done if the scanners go into more than 80% peak current. If you reset / power down the scanners, you probably see the same thing... normal operation for a bit, then the same distortion from your scanners. The distortion will continue to happen earlier every time you reset. I use the same thermal fuses and overrate them for the reason you list. When the scanner goes crazy, prepare to short an alligator clip or wire across the pumpkin-orange fuse on the X axis card and see if your image goes solid and back to normal. If so, solder a shorting wire across the thermal fuse. You won't have this problem again. Good luck! -Lasersmith

  5. #5
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    Can any one confirm this and or show me where the thermal fuse is?
    i bought these second hand off a member so im a bit worried to go messing with them, but i got s decent deal..

  6. #6
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    Sep 2011
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    Here's a picture of the fuse.... the yellowish-orange capacitor looking component, in series with the barrel fuse. You can see a circle around the component and the short on the back: Click image for larger version. 

Name:	solder short and electronic fuse1.JPG 
Views:	54 
Size:	31.1 KB 
ID:	27940 Good Luck! -Lasersmith

  7. #7
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    kiyoukan, I have to agree that the issue certainly appears to be the polyswitch as lasersmith23 has suggested. Most likely, there's nothing wrong with the polyswitch, it's just doing it's job. The problem could either be that the amp is a good bit out of tune or the scanner itself is failing. From looking at the video, the problem appears to me to be with the X axis scanner. I had an original DT-40 (precursor to the DT-40Pro) fail in a similar way. The failure ended up being caused by epoxy deep within the scanner that had a low melting temperature. So as the scanner heated up over time the epoxy began gumming up the rotor, requiring more current from the amp to get from point to point until it was tripping the poly switch.

    Here's what I'd do, first off, check the tuning. If that is good, swap the signal input to the scanners and make sure the failure stays with the same scanner. Next, I would swap the amps around, X scanner to the Y amp, etc. This will require a retuning. If the problem stays with the scanner then it's time for a new one. The newer DT-40Pro's have an epoxy that has a higher melting temperature and generally don't fail in this manner anymore.

  8. #8
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    How do i check the tuning if i only get a min or two before it goes out.
    if i reduce the scan angle they dont appear to go as quickly.
    Also the scanners dont even get warm, i checked everything. the only thing warm is the amp itself.
    The ilda pattern the inner circle is out of tune i know that for a fact.
    so how bad is it to short out that cap?
    if i short it out and the problem is fixed is that a bad thing?
    Should i worry about it?
    i bought these used from a member on here, so im a little miffed that there not working.
    If any body would be willing to lend me their time for a bit im sure we can find out how to fix this.
    I have skype with a web cam and a phone.
    Please msg me if you can help i will also be in the irc channel.
    but before they fail the images they display at 38k are amazing looking, 100x better than my 20ks

  9. #9
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    What scan angle are you running? how are they heat sinked?
    leading in trailing technology

  10. #10
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    Quote Originally Posted by kiyoukan View Post
    so how bad is it to short out that cap?
    if i short it out and the problem is fixed is that a bad thing?
    Should i worry about it?
    It all depends on the source of the problem. Lets just say that it is the epoxy failure. It will get worse and worse over time, to the point it will probably screw up the amp. You can short the polyswitch, no problem. Next, the fuse will probably fail, which isn't resetable, either replace it or short out the fuse as well. Eventually, your amp will fail or the scanner coil will go open. This is all if the epoxy is the culprit and just about exactly what I ran into. Trying to find the video I took of the problem, was a couple years ago now.

    Another thing you can do, you must be very carefull though, grab the edges of the mirror on the scanner and turn it back and forth. It should feel as smooth as can be with almost no binding. Check one, then the other and see if there's a difference. It may be subtle, but might be worth a shot.

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