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Thread: Help Me Select Parts to Repair and Upgrade these 1.2w Projectors (Pics Inside)

  1. #1
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    Moderator, Please Delete Thread
    Last edited by Majik; 02-19-2018 at 08:02.

  2. #2
    Join Date
    Feb 2007
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    Hi Majik,

    Yeah, this is what you get when you purchase the lower end Chinese projectors. As with many things, you get what you pay for. The good thing about purchasing low end stuff is that you can upgrade it without significant fear of breaking it as you wouldn't loose as much as botching the improvement of an expensive, higher quality build. That's how I started, anyway.

    Regarding your first question, the galvos in picture number one and on the left of the two in pictures 3-6) look like super-cheap open loop galvos. Open loop galvos are just too sloppy for graphics applications. You could do basic abstracts and basic beams with them, but they just aren't up to the task of graphics. The ones in picture two are 15Kpps closed loop or 20K closed loop scanners. The corners are not bad at whatever scan speed they are set for. I'm surprised they are the same model number as this is a huge difference in quality alone. Sadly, there is no saving or tuning those open loop scanners. Thankfully you can replace them fairly easily with a better set.

    The differences in the red modules is significant as well. A 655nm module is much deeper red than 638nm and much less bright to the human eye assuming the beam characteristics and power are similar. The 2x638nm may be single mode or multimode reds. Its hard to tell from the pics. In any case, the 655nm module is . . not ideal and something to target for upgrade after those open loop scanners.

    Its anyone's guess what the actual powers are from any of these modules without a meter, but if they were relatively accurate, I'd say the primary issue regarding the 'heavy blue' is a combination of a fat multimode blue beam (those are usually the worst beam spec of cheap red/green/blue modules) and not enough power out of the 532nm green modules. I'd say to target 200mw 532nm (or 520nm) for a better white. Even with these upgrades, you are still going to end up with a tight green beam, surrounded by fatter red and even fatter blue . . but you'll gain experience by upgrading!

    Finally regarding question #2, this is an issue with either a floating ground causing voltage on the modulation line to the blue module or a bias setting potentiometer that needs to be adjusted down a bit. Measure the voltage on the modulation line to the blue when the projector should be projecting nothing and see if its over 0V. If not, finding out what pot is what if they aren't labeled is going to be tricky. Maybe take some detailed pics of that module?

    Let us know what you find!

    -David
    "Help, help, I'm being repressed!"

  3. #3
    Join Date
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    Quote Originally Posted by Majik View Post
    I absolutely agree, and I understand that these are nowhere near the caliber of what you've built (they were only $450 brand new), but I do think they're a good platform to learn with.
    Definitely!

    However, the sloppy graphics are a fairly new symptom. Mind you, I've been using these projectors for several years (average of 10 hours per month). When brand new, the graphics were symmetrical between both projectors.
    OK, so I am likely wrong about the one set being open loop scanners. Although any set of decent scanners should have lasted longer than those have (assuming they weren't being abused), there could be several things that have gone wonky with them - from tuning issues to power supply issues. To be honest, it isn't worth trying to diagnose the problem with such a cheap set. I'd just replace them. For beams only, the AL-20K set that you mention should be fine.


    10-4. So how do I find a suitable replacement? I mean, I've seen modules with a wide variety of voltage and amperage requirements. I have no idea what I'm working with...

    Seems to me like the 638nm could be replaced with the 500mw Mitsubishi Modules on DTR?
    That one needs to be corrected which requires cylindrical lenses, a driver, a multimeter and a good bit of patience at a minimum. CDBeam, Absolom and others have shared their correction findings for several diodes over the years, so you can look at one of those threads to gain an idea about what would be required. Warning - those new diode findings threads are often as long and wrinkled as a . . . <insert your punch-line here>.

    Something like this 200mw 532nm MODULE on eBay? I have a few 50mw modules lying around that look similar to this case/heatsink. Is it easy enough to replace the diodes with a higher power rating and use the same driver? Or just swap the existing diode for a more powerful one? I have been known to solder a few things...
    Replacing the diode in a 532nm set-up is considered advanced work that even very seasoned builders wouldn't touch. You are better off buying as you discovered - although you generally want analog not TTL. TTL can only be turned on and off limiting a RGB projector to 7 colors, where-as analog can be dimmed to combine to make a near-infinite number of combinations. If the rest of your laser modules are TTL, then you'd be fine with the one your pointed out.

    Above my comprehension level. Floating ground? Bias setting potentiometer? How do I know where the modulation line is? And of course none of the pots are labeled. I can certainly take detailed pictures. I assume you want pictures of the driver? The module just has +/- wires running to it.
    There should be two sets minimum going to the blue driver. One is power in and the other is modulation in. There is also one set (possibly two) going from the driver to the diode module (diode power and possibly fan power). Trace the lines from the blue module back to the driver (likely one of those matching stacked boards). I'd guess the white pair of wires is your modulation in line. Just measure the voltage across that pair when the projector shouldn't be displaying anything and see if the voltage is greater than 0V. If so, this will lead to another set of instructions to diagnose the root cause. If not, you just need to adjust the bias pot down slightly. There are two pots on those boards, but I can't tell from the pic which is which. The other pot controls the power going to the diode, which would blow the diode if you turned it up too much. It should be fairly safe to dial down each pot counterclockwise a little (like less than one revolution) to make the static beam stop. Keep track of what you do to return the pot to the same place if you got the wrong pot - or better yet, attach a better picture of the driver so we can see which pot is which.

    If it's going to cost me $300 just to repair it to OEM, I might as well purchase a brand new one for not much more. If that same $300 will yield me a much better projector, I'm all in.
    Yup, understood. Purchasing new but cheap only gets you back to where you started though. Seriously, sometimes these things aren't worth the effort to fix, but in this case, I suspect it would be educational and relatively inexpensive.

    Quote Originally Posted by Majik View Post
    Now that I think about it...are their any popular and/or common build logs on this forum (or elswhere), with a materials list of commonly used components? . . but does anything similar exist for the laser community?
    Ahh, yes, somewhere buried in PL there are such things. In addition, Laser Enthusiast Meetings (LEMs) are a great place for education and on-the-spot assistance from kind, knowledgeable laserists. If you share your location, we can point you out to the closest one and badger you to attend it.

    Happy hunting!

    -David
    "Help, help, I'm being repressed!"

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