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Tektronix 465 Scope

Discussion in 'Electronic Design' started by Dick, Dec 21, 2004.

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  1. Dick

    Dick Guest

    My Tek 465 scope has developed a minor but annoying fault in its
    triggering circuitry but before diving into the guts of an old &
    faithful friend I would appreciate it if anyone who has experienced
    similar symptoms to those below could give me their thoughts on possible
    causes & (more importantly) how they fixed their particular version of
    the problem.

    1) My scope just won't trigger in the A Normal mode although a stable
    trace obtained in A Auto will remain displayed (and stable) in A Normal
    until I touch either A Trigger slope or polarity controls.

    2) I can stabilise a trace using the A Auto mode but only by adjusting
    the A Trigger Hold-off control rather than the A Trigger slope/polarity
    I would normally expect.

    3) Everything appears to be triggering correctly when I use the B
    Trigger.

    4) All other scope functions appear to be OK.

    I've checked these symptoms and they seem to be present what
    ever type of signal I'm inputting - sine/square, 1kHz - 1MHz, Ch1 or
    Ch2.

    I've got a set of battered circuit diagrams & layout drawings so
    should at least be able to follow up any ideas you experts might be able
    to pass my way.

    In the mean time many thanks for at least reading this posting
    and Merry Xmas & Happy New Year to everyone fra' Auld Reekie
     
  2. It sounds (reads) like a bad connection.

    By Ole Occam's razor, and a description of the problem - 'it works
    till I touch the knob' - my first guess is a dirty and/or worn
    synch selection switch or trigger level pot. The pot wouldn't
    happen to have one section for Ch. A and one for B and get
    bypassed in Auto, would it?

    If it were mine, I would first try a spritz of contact cleaner into
    the switch via the front panel slot (IIR465C). All contact
    cleaners are the same - mineral oil and alcohol - so the cheapest
    Radio Shack stuff works as well as anything. WD40 also works well.

    Getting to the switch or pot by disassembly I would save for last.
    There is an old adage "Fix anything long enough and you will _really_
    break it." And I wish I would remember that adage in time.

    Other likely causes are bad connector, crimp or solder joint. After
    that electrolytic caps.

    --
    Nicholas O. Lindan, Cleveland, Ohio
    Consulting Engineer: Electronics; Informatics; Photonics.
    Remove spaces etc. to reply: n o lindan at net com dot com
    psst.. want to buy an f-stop timer? nolindan.com/da/fstop/

    OP:
     
  3. Clean the switches with Radio Shack tuner cleaner.

    --
    Many thanks,

    Don Lancaster
    Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
    voice: (928)428-4073 email:

    Please visit my GURU's LAIR web site at http://www.tinaja.com
     
  4. Leon Heller

    Leon Heller Guest

    You need the Tekscopes group:

    Leon
     
  5. "Nicholas O. Lindan" <> schreef in bericht

    [snip]
    How true. Today I fixed something... all the way to the rubbish bin ;)
     
  6. Highland Ham

    Highland Ham Guest

    ==============================
    On various occsasions I have been told that WD40 is NOT the right cleaning
    agent for electrical systems involving plastic insulation re wiring, etc. I
    always use (non chlorinated) contact cleaner as available from Rat Shack and
    similar stores.
    Here in the UK I use contact cleaner supplied by Maplin.

    Frank GM0CSZ / KN6WH
     
  7. Have you cleaned the controls and switches? Electromechanical parts are
    the weakest link.
     
  8. Dave Platt

    Dave Platt Guest

    Ugh. and Ugh again.

    I'd raise three cautions about this advice:

    [1] My recollection is that Tek specifically warns against using
    most contact cleaners on, or around, certain of the internal
    controls (e.g. the attenuator switches). These switches are
    apparently quite sensitive to contamination, as they deal with
    high-impedance signals. Spraying an oil-and-alcohol contact
    cleaner anywhere in their area might very well contaminate them.

    IIRC, Tek's recommendation is to use pure isopropyl alcohol, and
    a small clean brush, for cleaning contacts.

    [2] Not all contact cleaners are the same. Many used for sensitive
    equipment are "zero-residue" types - they have a cleaning solvent
    and propellant, but do not contain any sort of lubricant, and are
    intended to leave nothing behind on the contacts. Even among the
    contact treatments which do contain a lubricant of some sort, there
    is wide variation in the type of solvent used (some use alcohol,
    some use a hydrocarbon or chlorinated/fluorinated hydrocarbon)
    and the lubricant used (some use mineral oil, some a polyphenyl
    ether, others something else entirely). It pays to use the right
    combination for the job.

    [3] I would not use WD-40 as a contact cleaner, on anything less robust
    than an electric motor. It's not formulated for that purpose
    (in fact, it's not really formulated as a long-term lubricant!)
    and it is notorious for getting gummy and attracting dust over
    the long run.
     
  9. At the moment I'm having a fight with my Dynatek. So I looked up this
    section in the schematics. Triggering looks simple. The trigger signal is
    enabled/disabled by the outputs of a flipflop (LS74 here) which is
    set/cleared by the channel selector switch. Here the switch is floating to
    select Channel 2. So a bad contact will select channel 2. It looks almost
    too simple, but an attack with contact cleaner may cure your old friend.

    Carel
     
  10. NONONONONONONO!!!! DEFINITELY NOT!!!!!

    All contact cleaners ARE NOT the same! Never have been, never will
    be, and the proper ones for degreasing electronic equipment do NOT
    contain any mineral oil!

    I speak from knowledge gained over 25+ years of pro experience in
    the fields of radio, electronics, and computers. NEVER, under ANY
    conditions, use WD40 inside a Tektronix 'scope or any other electronic
    device! It leaves an oily residue which will actually ATTRACT dirt and
    gunge, and make the problem worse.

    If you value your test equipment, don't cut corners on the stuff
    you use to maintain it. Check the Tektronix service manual for the
    recommended cleaner formulation, and get it from a quality electronics
    supply place (Radio Shack does NOT come under that category as far as
    I'm concerned).

    I can tell you from personal experience that CRC 'CO Contact
    Cleaner' works very well, and it is plastic-safe so you won't damage the
    innards of the vertical attenuator assemblies.

    It may cost a little more up front, or be a little harder to find,
    but you won't be risking the long-term life of said equipment.

    Happy hunting.

    --
    Dr. Anton T. Squeegee, Director, Dutch Surrealist Plumbing Institute.
    (Known to some as Bruce Lane, ARS KC7GR,
    kyrrin (a/t) bluefeathertech[d=o=t]calm -- www.bluefeathertech.com
    "If Salvador Dali had owned a computer, would it have been equipped
    with surreal ports?"


    -----------== Posted via Newsfeed.Com - Uncensored Usenet News ==----------
    http://www.newsfeed.com The #1 Newsgroup Service in the World!
    -----= Over 100,000 Newsgroups - Unlimited Fast Downloads - 19 Servers =-----
     
  11. Roy Lewallen

    Roy Lewallen Guest

    A number of the switches on the 465 use PC board pads as contacts. They
    have heavy gold plating, but eventually the gold wears off. When that
    happens, the switch is dead and as far as I know can't be repaired. You
    might be able to squeeze a little more life out of it by cleaning, but
    in any case I'd be very careful not to use a cleaner with any abrasive
    qualities. If cleaning doesn't cure the problem, worn pads might be the
    cause.

    But by all means check with the 'scope newsgroup. I'm sure you'll find
    folks who have had a lot of experience with the 465, and some might even
    know of some kind of fix or replacement for worn switch contact pads.

    Roy Lewallen, W7EL
     
  12. Jim Yanik

    Jim Yanik Guest

    On TEK LF or HF cam style contact switches,do NOT use mineral oil-based
    cleaner/lubes.Take some 99% isopropyl alco,wet a narrow paper strip,and
    slide under the closed contact,and move back and forth.These cam-style
    switches have VERY low wiping force,and any oil,grease,or film will cause
    intermittents or opens.

    I suspect a calibration may improve his triggering,too.
     
  13. Jim Yanik

    Jim Yanik Guest

    No.Use 99% isopropyl alcohol.
     
  14. John Miles

    John Miles Guest

    You know, it's funny how often these debates flare up over a subject as
    mundane as contact cleaner. "My tuner cleaner is better than your tuner
    cleaner. Your tuner cleaner should be used only in Ukrainian opposition
    candidates' minestrone. My tuner cleaner costs more than HP printer
    ink. If you spray your tuner cleaner on a Tektronix 465, it will
    trigger a resonance cascade and gate in alien overlords from the planet
    Xen." Yadda, yadda, yadda.

    Despite all the gurus out there forking the evil eye at WD-40, I sure
    seem to own a lot of stuff that still works fine after being sprayed
    with WD-40 over the years (decades, in some cases). Yeah, I know.
    "Data: n, plural of 'anecdote'."

    Some of these gurus are admittedly respected veterans of companies such
    as Tektronix, with whom mere mortals are loath to argue. All I can say
    is, those switches must not have been of the greatest quality in the
    first place, or the gurus wouldn't have to spend so much of their time
    on Usenet warning people against hosing them down with WD-40.

    Just sayin', is all. No disrespect intended. :)

    -- jm
     
  15. "John Miles" <> schreef in bericht

    [snip]
    LOL. Well, some switches on oscilloscopes are very fragile with many,
    many contacts, and rather low contact pressure. Sometimes hermetically
    sealed too, so you can even use a spray can of Spam or shaving foam and
    it won't hurt a bit ;)
     
  16. Roy Lewallen

    Roy Lewallen Guest

    The discussion about contact cleaner isn't altogether mundane.

    I worked at Tek for many years, although I'm certainly not a guru when
    it comes to oscilloscope maintenance. But I do recall one experience
    with cleaning solvents and board-mounted switches.

    Before introducing a new instrument, we went through a lengthy process
    of building and testing prototypes, which I described some time ago in
    this newsgroup. In one group, it was our practice to borrow some
    assemblers from production to build the prototypes. One afternoon I was
    looking at some units they had built, after they had left for the day,
    and saw that the plastic of some switch bodies was very badly crazed --
    they were covered with tiny cracks. Some experiments with bottles of
    solvent we found in some of the assemblers' work areas pinned it down to
    one particular liquid. The problem was one of the ingredients, which was
    a relatively common solvent of the time. Unfortunately, I don't recall
    which one -- it was something pretty mild as solvents go, like toluene
    or Freon, not a relatively strong solvent like acetone, which we all
    knew better than to use. We found out that the solvent had been banned
    from production, but the assemblers kept a supply out of sight because
    it was really good at removing flux.

    The lesson is that even some normally pretty innocent solvents can
    destroy some plastics. Other components can also be ruined by various
    solvents, so that's another reason to use some caution. As just one
    example, it was found that Freon and its relatives would migrate up the
    leads and into even pretty well sealed radial leaded aluminum
    electrolytic capacitors, corroding the insides and causing premature
    failure. This was solved by improving the end seals, but only after a
    lot of the older type reached the field, some on boards having been
    washed with Freon. Of course, Freon is no longer used, but there are a
    host of other potential problems. It's ultimately up to you to decide
    whether you want to experiment with your scope.

    As for WD-40, I love the stuff and use it on all kinds of switches and
    electrical components. But I mentioned a short while ago that the cam
    switches in the 465 and some other scopes use PC board pads for
    contacts, and when the pad's gold plating is gone, the switch -- and the
    scope -- is dead. So it doesn't seem like a good thing to me to use a
    cleaner on those that'll leave a film which can collect dust or anything
    abrasive.

    I don't agree that a switch's ability to withstand WD-40 or any other
    particular chemical is an indicator of its quality. But we all have our
    own criteria we use to judge.

    Roy Lewallen, W7EL
     
  17. That was also my impression. But I have used it on plastics and
    have not found any problems after 20 years. Famous last words,
    I know. I have used it as a contact cleaner with great success.
     
  18. It is possible to re-plate the gold. But imagining the circuit board
    it may be impossible to mask the components. Aw, what the heck - gold
    plate the whole thing and screw it to your Hinkley yacht.
     
  19. Jim Yanik

    Jim Yanik Guest

    I worked for TEK for 21.5 years as a service tech in 2 of their field
    offices;repaired and cal'd a lot of scopes and other TEK products.
    Considering how longlasting and popular the 465 is,that's not a very smart
    sentence.The same HF and LF cam switches were also used in the high-
    performance 7000 series lab scopes.
    Same here.
     
  20. Roy Lewallen

    Roy Lewallen Guest

    If there's any disagreement between what I say and what Jim says about
    maintaining Tek scopes, listen to Jim and not me. He was there in the
    trenches; I wasn't.

    Roy Lewallen, W7EL
     
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