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Metrologic ML855 HeNe Laser

Discussion in 'Electronic Repair' started by [email protected], Sep 10, 2013.

  1. Guest

    Hi Folks,

    I'm a high school physics teacher, and just found an ML855 HeNe Laser from 1989 in a storage closet at my school that I'm trying to get to energize. My degree is in electrical engineering, so I'm not unfamiliar with troubleshooting electronics, but I've never worked with laser electronics, especially not from the 80s. The device requires a key to activate a switch, which Icannot find, but I was able to use a paperclip, while the device was unplugged, to attempt to rotate the lock mechanism into the "on" position. Now, I'm not sure if this rotated the actual switch or just some part of the lock, so the source of this entire problem could be that I am missing that key.. If this is so, how could I obtain a replacement key for this unit?

    If this is not the case, and you think my "jimmy the lock with a paperclip"method should have turned it on, does anyone know of any common failures with this model laser? The power light on the back does not even turn on, soif it is a failure, I imagine it's with the power supply.

    Any and all suggestions would be appreciated.

    Thanks
     
  2. tm

    tm Guest

    You should be able to get a key made by a locksmith. Baring that, key
    switches are easy to find with new keys. You could remove the key switch and
    install a common toggle switch for trouble shooting the laser tube.

    Most likely you will find the tube will not start. Over the years, the He
    gas has migrated through the glass and the seals and will be at low
    pressure.

    If this is the case, It is possible to soak the tube in a He atmosphere and
    He will diffuse back into the tube. This will take a few days to do and you
    will need to check it frequently

    tm


    Hi Folks,

    I'm a high school physics teacher, and just found an ML855 HeNe Laser from
    1989 in a storage closet at my school that I'm trying to get to energize. My
    degree is in electrical engineering, so I'm not unfamiliar with
    troubleshooting electronics, but I've never worked with laser electronics,
    especially not from the 80s. The device requires a key to activate a switch,
    which I cannot find, but I was able to use a paperclip, while the device was
    unplugged, to attempt to rotate the lock mechanism into the "on" position.
    Now, I'm not sure if this rotated the actual switch or just some part of the
    lock, so the source of this entire problem could be that I am missing that
    key. If this is so, how could I obtain a replacement key for this unit?

    If this is not the case, and you think my "jimmy the lock with a paperclip"
    method should have turned it on, does anyone know of any common failures
    with this model laser? The power light on the back does not even turn on, so
    if it is a failure, I imagine it's with the power supply.

    Any and all suggestions would be appreciated.

    Thanks
     
  3. Paul Drahn

    Paul Drahn Guest

    IF there is a number on the metal part of the switch, a locksmith can
    make you a key based on that number.

    Paul
     
  4. bypass the switch.

    there's no reason to have a keyswitch on some old dead laser.

    You'll also find a new keyswitch from digikey or newark will cost less
    than talking to a locksmith.
     
  5. tm

    tm Guest

    Wow, you need to find a better locksmith. I needed a key for a portable
    pulsed x-ray source and took it to a good locksmith. He looked up the lock
    number and sold me two keys for $6 something.

    I agree with you that the laser will most likely be dead but might be
    recoverable with a He soak.

    I am pretty sure that a key switch is required by the FDA depending on the
    laser power. Considering he is a HS teacher and may be using this around
    students, the key switch is a good thing to have.


    This space reserved for snarkey comments.
    -----------------------------------------------------------------
     
  6. Guest

    Thanks all. I'll pop it open and hook in a rocker switch or something like that (when no students are around, of course). Maybe I'll get lucky and the tube will still work. Otherwise, I'll talk to some friends in labs about a Helium soak.

    Thanks again.
     
  7. Guest

    Well if that doesn't work. What's a HeNe do, that you can't do with a red diode laser? ~$10 or so.

    George H
     
  8. Actually quite a lot.

    If it is less than about 30 years old, the tube is hard-sealed and
    doesn't really leak. An ML855 could be function like new.

    Bypasss or replace the switch and see what happens.

    Just be careful of the line voltage and high voltage inside!

    --
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  9. Roger

    Roger Guest

    "Cydrome Leader" wrote in message
    bypass the switch.

    there's no reason to have a keyswitch on some old dead laser.

    You'll also find a new keyswitch from digikey or newark will cost less
    than talking to a locksmith.
    -----------------------------------------------------------------------------------------------------------------------------
    I've worked with HeNe tubes before. The ones I've seen are a foot to 1.5
    feet in length; they are usually 1 milli-watt to 5 milli-watts laser output
    power. You would not want to get the beam directly in your eye, it could
    cause some damage. I have heard that the eye very quickly turns to avoid
    being damaged though. The little laser pointer that you can buy all over
    that work off of watch batterys are in the same range of power. A HeNe tube
    puts out a much better quality of laser light and more coherent than a
    little laser pointer and it will be most likely red light. You won't see
    the beam at these low power levels, just a intense bright spot on what ever
    you aim it at. Note that the brightness of the spot is much brighter that
    our eyes can determine. If it is low power like I'm guessing, I don't think
    you need the key switch; just replace it with a toggle switch, I think US
    and Canada changed the rules on low power laser otherwise you wouldn't be
    able to by a laser pointer toy.

    The power supply to power the HeNe tube run around 2000 volts and some put
    out a pulse to start the tube up to a voltage of around 10,000 volts. They
    draw a few milliamps. So watch out not to shock yourself if you touch
    anything inside the chassis. Also note that after the power is turned off,
    the laser tube holds a charge on it and if you touch the wrong area you'll
    get an unpleasant shock - guess how I know this :)

    Good luck!

    Shaun
     
  10. Leif Neland

    Leif Neland Guest

    Roger kom med denne ide:
    Sign: Don't look into laser with remaining good eye.
     
  11. Guest

    Hi Sam, What kind of things? We sell both a HeNe and a diode laser with our interferometery apparatus.
    http://teachspin.com/instruments/moderni/index.shtml

    The HeNe has a fixed wavelength.... and as it warms up you can watch the coherence length 'swish' around as the different longitudinal modes cross over the gain curve. But that seems like a bit of an esoteric difference for the 'normal' high school laser application.

    What else do you have in mind?

    George H.
     
  12. Guest

    Hi Shaun, Certainly the beam profile is better in a HeNe.

    I'm not sure what you mean by 'more coherent', but for the few diode lasers I've looked at - compared to the short cavity HeNe that I have, the diode lasers had a longer coherence length.
    (Which struck me as a bit weird the first time I saw it... I had this mistaken belief that the coherence length was related to the cavity length.)
    I'm not sure if the long cavity HeNe's have a longer or shorter coherence length when compared to the short cavities... Perhaps Sam will educate us.

    George H.
     
  13. chuck

    chuck Guest

    09/10/2013On Tue, 10 Sep 2013 23:41:52 +0200, Leif Neland

    I worked for a company in the mid 80s that sold Pioneer Laser Disc
    players. A high school kid came in one day who experimented with the
    laser tubes from these players. He had holes burnt into the iris of
    one of his eyes. Chuck
     
  14. There's a lot one can do with respect to the longitudinal modes, though
    perhaps that is a bit of a stretch for an intro to lasers in high school.

    But one can do some nice interferometry experiments with not much additional
    equipment.

    In fact, I see you your Web site that you do some of these things.

    A Fabry-Perot with a common random polarized HeNe laser is a work of art. ;-)

    The beam quality is also a lot better than most diode lasers (divergence,
    beam profile).

    With some you can put another mirror in front or in back of the laser
    (if accessible) and get 1 or more of the other HeNe wavelengths.

    I can go on and on..... :)

    Contact me directly via repairfaq.org if you'd like.
    --
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  15. It's a crap shoot. Some diodes have exception coherence length but
    many/most are very short.

    --
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  16. IF they are soft-seal. If newer than around 30 years of age, they will be
    hard-seal with an essentially infinite shelf life.

    Running a soft seal tube that has a decently bright discharge may get it
    to come back to life after anywhere from a few hours to months.

    --
    sam | Sci.Electronics.Repair FAQ: http://www.repairfaq.org/
    Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
    +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
    | Mirror Sites: http://www.repairfaq.org/REPAIR/F_mirror.html

    Important: Anything sent to the email address in the message header above is
    ignored unless my full name AND either lasers or electronics is included in the
    subject line. Or, you can contact me via the Feedback Form in the FAQs.
     
  17. Shaun

    Shaun Guest

    "chuck" wrote in message
    09/10/2013On Tue, 10 Sep 2013 23:41:52 +0200, Leif Neland

    I worked for a company in the mid 80s that sold Pioneer Laser Disc
    players. A high school kid came in one day who experimented with the
    laser tubes from these players. He had holes burnt into the iris of
    one of his eyes. Chuck
    ------------------------------------------------------------------------------------------------
    Bullshit!

    A read laser does not have that much power. If it was a CD Burner - then
    that could happen. With a regular CD player, the laser might damage the
    Retina which is at the back inside of the eye ball, it converts what we see
    into a signal that our brain decodes as an image.

    I would still like to know why it is allowed that anyone can buy a handheld
    diode laser under 5 milliwatts without any safeties or adult supervision.
    They can do lots of damage!

    Roger
     
  18. Guest

    Hi Sam, Thanks for the response. You're talking about sending the laser into a F-P and looking at the output? A flat mirror F-P (Etalon), a confocalcurved mirror F-P, or something in between?
    Yeah there are lots of fun things if you allow for access to the cavity. Irecall fondly an argon laser in grad school, that was equipped with a grating and mirror on one side... you could tune through all the Argon lines. There is a certain beauty in the 'pure' blue colors.
    Thanks Again,

    George H.
     
  19. chuck

    chuck Guest


    The kid did have holes in his iris, maybe he experimented with other
    more powerful lasers that I didn't know about. Chuck
     
  20. Guest

    OK that's good to know. It'd be nice if someone had a list of good diode lasers. The one we use is from US lasers M650-5I. ~$33 from digikey. We have a couple of others but I never looked at the coherence length.

    George H.
     
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