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old TEK 475 problem

Discussion in 'General Electronics' started by Jeffrey Dutky, Aug 5, 2003.

  1. I've got an old TEK 475 that belonged to my father and hasn't seen the
    light of day for at least ten years. I powered it up recently (after
    'baking' it in the attic with a dehumidifier for a few weeks) and it
    seems to be basically working, except for a little trouble with
    channel 2:

    When I connect channel 2 to the built-in calibration signal, rather
    than the expected square wave, I get something that looks like this
    (channel 1 is also
    connected to the calibration signal):

    _________ _________
    | | | |
    | | | | channel 1
    | |_________| |_________



    \ \
    `-------- ,-------- `-------- ,-------- channel 2
    / /


    I recognize this as an 'integrator' (Art of Electronics term) which, I
    guess, means that there is a broken connection in the channel 2
    electronics. Any ideas on where to start looking for the problem (or
    if I'm on the wrong track, what I should be looking for)?

    Another issue: I have two P6075A 10X probes for the scope, one of
    which is marked "Bad". I haven't seen any difference in the readings
    between the two probes (swapped on channel 1) but I've only been
    looking at the, relatively low frequency, calibration signal. There
    may be some obvious deficiency at high frequencies. Does anyone have a
    suggestion where I could obtain another P6075A, or what other probe I
    could use as a substitute?

    -- Jeff Dutky
     
  2. Tweetldee

    Tweetldee Guest

    Yep, you're thinking along the right path. The broken connection that
    you're looking for is likely to be a tarnished or corroded vertical
    sensitivity switch contact in channel 2. Take the covers off the scope so
    you can get to the switch and see if you can get a cotton swab that has been
    dipped in 91% isopropyl alcohol, or denatured alcohol. Be careful not to
    get the common rubbing alcohol, because that may contain some contaminants
    that you don't want to leave behind. Scrub the contacts until they are
    bright and shiny. Actually, that's stretching it a bit.. just clean them
    until the areas that make contact are clean and tarnish-free.
    You might spray a cotton swab with a good tuner cleaner and CAREFULLY swab
    it onto the contacts. Be very careful not to get any of the lubricant that
    is in the tuner cleaner on the body of the switch. That's a pretty good
    scope, and cleanliness is important in this area.
    With a bit of care and luck, that should get your scope back into service.
    Good luck!!
    As for your probes, use Google to search for sources of used probes. I seem
    to remember a web site that specializes in used probes, advertising
    themselves as "dirt cheap probes" or something like that. Another great
    source for probes is at a hamfest, the larger the better. Find one that's
    scheduled within driving distance and visit. You'll probably find more than
    probes to spend your cash on.
    Cheers!!!
    --
    Tweetldee
    Tweetldee at att dot net (Just subsitute the appropriate characters in the
    address)

    Time is what keeps everything from happening all at once.
     
  3. Jim Yanik

    Jim Yanik Guest

    Instead of using a cotton swab and getting cotton fibers wrapped around the
    contacts,use a narrow strip of clean white paper,slide it under the closed
    contact,then wet with a drop of alcohol(99% isopropyl).Then move the paper
    srtip back and forth to clean the contact and pad.Tedious,but effective,and
    you will not bugger up the contact fingers.Don't use tuner cleaner as some
    will attack the polypropylene PCB material,and some tuner cleaners also
    leave a lube film which is not good for TEK HF cam sw.contacts.(very low
    wiping force)

    I'm an ex-TEK service person,21.5 yrs with TEK.
     
  4. A E

    A E Guest

    Hmmm, what about NU-TROL control cleaner? It's tetrafluoroethane. Cleans like a
    champ, do you know if this can damage old Tek stuff? So far, it hasn't in my
    careful use of the stuff.
     
  5. Rich Andrews

    Rich Andrews Guest

    (Jeffrey Dutky) wrote in
    For new probes, www.probemaster.com looks pretty good to me. I would think
    that you could repair the one you have.

    r
     
  6. Kevin Carney

    Kevin Carney Guest

    It could also be one of the compensation blocks that plug into the
    attenuator. I belive they are marked 2X, 5X and 10X. They way to tell is
    after doing the cleaning thing and if it doesn't fix the problem, swop the
    attenuation blocks from the good to the bad channel. Do one block at a
    time. Take Care, Kevin

    --
    change .combo to .com for correct email

    ***************************************************
    "We ought always to know precisely why a given job
    is done in a particular way, and why it is done at
    all, and why it can't be done more efficiently,
    if it must be done at all."-- T.J.Watson

    ***************************************************
     
  7. Jim Yanik

    Jim Yanik Guest

     
  8. JeffM

    JeffM Guest

    \ \
    Actually, it's a differentiator (high-pass filter), which says that
    the series capacitance is high in value (possibly open--totally capacitive)
    when compared to the shunt element (resistor || capacitor).
     
  9. Jim Adney

    Jim Adney Guest

    I'm not so sure this is good advice. I think this section of the 475
    uses a very delicate cam switch which was only to be cleaned with pure
    methanol. You also don't want to get cotton fibers in there; they
    could stay behind and cause more problems, or snag the contacts and
    ruin the switch. Don't take my advice on this, you should see if your
    father had the 475 manual, because this will explain it all correctly.

    There is something you CAN do right away. Rotate the vertical
    sensitivity knob back and forth a few times just to see if this helps
    at all. Move the AC-GND-DC switch back and forth a few times likewise;
    it should be on DC for the test above. Any of these switch contacts
    can get a bit of dust in there which could cause such a problem, so
    it's useful to find out exactly where the problem is before you start
    trying to clean things.

    -
     
  10. Andy Cuffe

    Andy Cuffe Guest

    I was able to repair a bad attenuator block on one of my Tek scopes by
    resoldering the connections to the ceramic substrate. The plastic cover
    on the attenuator was easily removable. I'm not sure if the 475 uses
    the same type. In this case it was only some V/div that didn't work.
    If all settings aren't working I doubt it could be a bad attenuator.
     
  11. Lionel

    Lionel Guest

    I don't suppose you've got any tips on where I can obtain
    (electronically, if possible) a user manual & a service manual for my
    fantastic old Tek 2235 CRO?
    (It hasn't been calibrated in the 10 years I've owned it, but it still
    works beautifully!)
     
  12. Jim Yanik

    Jim Yanik Guest

    First,Ebay.
    Also;
    MANUALS SOURCES

    TECH SYSTEMS 1-800-435-1516
    SYNERGETICS SURPLUS 520-428-4073
    PEPPER SYSTEMS 214-353-0257
    MANUALS PLUS 206-531-8031
    US SURPLUS 410-750-1083
    E-MAIL:

    Tektronix Used Manual Sources:
    1. Deane Kidd 27270 SW Ladd Hill Road Sherwood, OR 97140, 503 625-
    7363
    (also has some parts)
    2. Ed Matsuda, P.O. Box 390613, San Diego, CA 92149, 619 479-0225
    voice, 619 479-1670 fax
    3. Manual Merchant: Linda Perkins, PO Box 927792 San Diego CA 92192,
    619-642-0785, -0885 fax,
    4. W7FG Vintage Manuals, 3300 Wayside Dr., Bartlesville, OK 74006,
    800-807-6146
    5. Manuals Plus, P.O. Box 549, TAD #601, Tooele, Utah 84074, (801)
    882-7188, (801) 882-7195 Fax

    Some of these may be out of date.
     
  13. JeffM

    JeffM Guest

  14. KLØS

    KLØS Guest

  15. KLØS

    KLØS Guest

    I tried replying to the Grantl who asked for additional info but after
    removing the "NOSPAM" part of your address it still bounced. So here's the
    info on getting to the site:

    ----------
    Grant-- try going first to:

    http://www.logsa.army.mil/

    Select "Publications and Forms"

    which should get you to:

    http://www.logsa.army.mil/pubs.htm

    then select "Electronic Technical Manuals Online"

    which will roll you down to:

    "Go to Electronic Technical Manuals Online" - click on this link which
    takes you to:

    http://www.logsa.army.mil/etms/online.htm

    If you accept their terms click on "I accept" which takes you to:

    http://www.logsa.army.mil/etms/welcom1.htm

    Choose "Enter the Site" [Note the disclaimer that you have to login if
    accessing anything but public release manuals and that you have to have 128
    bit encryption engaged. That should bring you to:

    http://www.logsa.army.mil/etms/find_etm.cfm

    which is the search page; click on "TM Title Text" and enter "tektronix" and
    scroll down to hit "search" which should get you to:

    http://www.logsa.army.mil/etms/show_etm.cfm

    where if you scroll down and look CAREFULLY you'll find Tek 475 material
    which you can then download (it's in .pdf format).

    You may have to go thru this entire process to establish the fact that you
    accept their terms....there's probably a cookie in my system that lets me go
    straight to the search page. I've found a number of good references here
    for text equipment.

    Let me know if you have any luck...

    Dino KLØS/4
     
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