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Thread: Leadlight pot is trashed

  1. #1
    Join Date
    Feb 2005
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    Default Leadlight pot is trashed

    We have all seen the post " and now the pot has no effect". Now I got one ( or 2) that does that. I think the wiper destroys the resistive stuff if you move it too much. I think I will take it off and use a big pot to set my current. And then use SM resistors out of a old hard drive or something to permantly set current.

    Now, I think I have seen that the Leadlight pot is a 2k. So any 2 resistors need to add up to 2k.. Or close. Let's say I set current with the big pot. Unsolder it and test on DVM. And say it reads 1900 one way and 120 ohm's the other way.

    Is it a good idea to make up these 2 resistors and set current perm like?

    Any thought's?

  2. #2
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    Default

    if the pot has no effect on the output (and your talking about 105 model) then the chrystal is weak\bad !
    And trying to push more power into the diode will NOT give any stronger beam!

    The only thing u will notice is that it get`s strong then it starts to dim ....

  3. #3
    Join Date
    Jan 2005
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    lancaster Pa. USA
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    Default

    you can use pretty much any variable resistor to replace the broken one .
    its the size factor that is the troublemaker.
    a 5k is more common than a 2k. setting the level might be a bit more difficult but it will work
    Those who stand for nothing, Will fall for anything.

  4. #4
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    Heres a schematic of the leadlight driver board .. found on cpf

    [/img]http://www.matrixscreensaver.150m.com/images/my-sch.jpg
    Those who stand for nothing, Will fall for anything.

  5. #5
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    Default

    Heres a schematic of the leadlight driver board .. found on cpf

    [/img]
    Those who stand for nothing, Will fall for anything.

  6. #6
    Join Date
    Feb 2005
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    Florida
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    Default

    Thanks guys.
    This leadlight 105 came from Vital*Spririt and was doing around 4mw. The hole was already drilled so naturally I turned it up a little( all the way). I was worried that with the hole under the button already there, that it may not go up much. But it did like 12-14mw with the pot mod. Never able to leave stuff alone, I decided to check polar alignment on the diode. So I turned the pot down a little before pulling the module out of the case. About 1/10 of a drop of acetone and I was able to rotate the diode without removing the driver. As it turns out , the thing was already at the best spot and had a alignment mark on the brass in line with the red dot. So I locked it back down in the same spot and proceded to turn the pot back up.

    But now it does not increase output. It will go down in power and even off at this point. So I move it around a few times(letting it rest some ) and the highest point is lower and lower output. But after I move it a few times, it will no longer go off. And it quickly gets to the point where the pot has no effect at all.

    Assume the MCA is bad and the pot and driver are good. And say the lowest current is 130MA. I figure 130ma would be below threshold for the vanadate. But you cant turn the beam off with the pot. With a bad MCA, I would expect that it would be easier to get below threshold for the vanadate with a good driver.

    And no matter where I set the pot, the diode gets really hot very fast. It starts to heat the driver board thru the diode leads and I cant run it more than 5 seconds.

    So maybe tonight I will remo the switch and pot and do some testing.

  7. #7
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    If your laser gets really hot quick, you might be beyond the point of no return!
    have you measured the current when you are getting the "hot diode"

    if it is beyond 500 ma you might have to buy a new laser!
    or a diode anyways. there is NO, repeat NO margin of error

    when dealing with circuits of that small size you need to make sure you keep it clean.
    small solder balls can destroy your work real quick.

    after replacing or changing anything best to use 99% alcohol and a brush to clean the area before turning on power.

    and above all, use anti static mats, tools, whatever . if none of this is available , be very carefu what you touch.
    one static charge and poof.. dead laser.. not even a whimper will you notice.

    Sorry if you know some of this allready,
    but this is a public forum and if there is something here that helps anyone. I will have done my job.
    now if i can get paid for this somehow
    Those who stand for nothing, Will fall for anything.

  8. #8
    Join Date
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    Default

    The current runs 350-380Ma. This is for the whole thing, not just the diode. And the current jumps as you move the pot, but never leaves the 350-380 range. But the current is not steady when not moving the pot. I thouht perhaps if the resistive element of the pot was damaged, that the diode may get too much. But this does not seem to be the case, as I would expect close to 500ma or more. It could be that the driver chip is acting wacky, and my meter is not catching pulses that could heat the diode. I dont have a scope or any way that I can think of to see something like this.

    As far as soldering, I'm not as young as I used to be. So I have to use a 25mm telescope eyepiece for inspection. Used like a jewelers thingy. SUPER ZOOM. And I use a temp controlled 24v ( think 24v) grounded tip iron around 600 F. And rosin/flux pcb cleaner spray that evaporates..

    As for ESD. I live near the beach in Florida with high humidity and have never had much trouble. I handle diode's and CMOS chips in ways that would make people cringe. I like to sit in front of the TV with 2 tray tables to play with my toys. And I dont have a ground handy unless I have the iron in there. Lazy will get me one day.

    I need to get another pointer. Because I dont have any "known good" parts to test with. The problem is that every time I pull one of these apart, it seems to end up in the known bad pile.

    .

  9. #9
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    Feb 2005
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    Florida
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    Default

    I been thinking ( I like to try new things)....Maybe I will get a LM 317 out of the pile , put 20 leds on a breadboard, and set 300ma. Then pull the driver off the leadlight and try the "known to be doing 300ma at 3v" test.

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