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oscilloscope question

Discussion in 'Electronic Repair' started by Dave, May 4, 2007.

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  1. Dave

    Dave Guest

    I'd like to know what the minimum useful bandwidth is for an oscilloscope to
    be used for general TV and audio equipment troubleshooting and repair. I've
    stumbled across a 20MHz dual-trace scope at a second-hand store, it appears
    to work and they only want $50 for it. The brand is "Leader" which I'm not
    familiar with. Comments?
  2. Tim

    Tim Guest

    Hmmm, I recall that Leader had a fairly good name in the past. And the
    company I worked for bought me a 20Mhz dual trace model to do service
    work on video equipment. Of course this particular unit maybe modified
    or damaged in some way, but I would likely buy it if I knew it hadn't
    been abused.

    - Tim -
  3. ian field

    ian field Guest

    About 10 to 20Mhz is adequate for most CRT TV diagnosis, in my experience -
    the more experience I gained at servicing, the less I needed a scope to
    diagnose most day to day faults. IMO it might be better to get by as cheap
    as possible until you assess the requirements for servicing flat panel TVs,
    there might be other instruments that prove more useful than a CRO.
  4. N Cook

    N Cook Guest

    An isolation transformer may well cost the same again.
    For TV work and isolation transformer is first priority and then a 'scope.
    Somewhere in the list comes an ELCB/RCCD/GFCI
    Then a variac for diagnosing crowbar problems etc
  5. Dave

    Dave Guest

    I've already got an isolation transformer and GFCI. What are ELCB and RCCD?

  6. Dave

    Dave Guest

    Sorry, two seconds on my part answered my own question. Hate it when people
    post lazy questions to newsgroups.
  7. Guest

    20MHz is more than enough.

  8. Charles

    Charles Guest

    Offer them $35. Leader scopes are decent and the BW is fine for your use.
  9. And have them add the schematics so you can repair it yourself.
    Check wether Leader used any proprietary semiconductors and
    wether the CRT has burnt in trace.
    You may well want to check eBay for comparable offers, too.

  10. James Sweet

    James Sweet Guest

    More important than burn is to make sure the CRT can still produce a sharp
    trace. It should only take a few minutes to plug it in and verify basic
    functionality though. For 50 bucks it's hard to go wrong on a working 20 MHz
    scope, that's more than enough scope for the average hobbyist.
  11. Franc Zabkar

    Franc Zabkar Guest

    I have a Leader LBO-514 10MHz scope. It seems to be adequate for most
    jobs. I had to fix about 50 dry joints, though. If yours is anything
    like mine, you will need to redo all the interconnects between the top
    and bottom layers of each PCB.

    - Franc Zabkar
  12. Lionel

    Lionel Guest

    Other names for GFCI. They're called all sorts of different names
    around the world.
  13. Dave

    Dave Guest

    Yeah, another one of those unfortunate examples of the old axiom "there
    ain't no such thing as a free lunch".
  14. Dave

    Dave Guest

    When the scope is powered up, it has a white line which starts to cross the
    screen from left to right. The line gets about halfway across, then
    disappears and doesn't come back.

    Does this mean the scope is disfunctional? I thought it should have a
    steady horizontal line when it's turned on with no inputs.
  15. bz

    bz Guest

    That depends on how the triggering is set.

    You could be set for single sweep. It almost sounds like that and a slow
    sweep at that.

    You could be set for triggered sweep and not have a trigger.

    You need to play with a properly working scope for a while to learn how to
    use it and then you can test a questionable scope.

    bz 73 de N5BZ k

    please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
    infinite set.

    remove ch100-5 to avoid spam trap
  16. ian field

    ian field Guest

    The trace sweeps from left to right and should be blanked on the return
    If the trace only goes half way across the screen try centering it with the
    horizontal shift control.
  17. The centering is set to the left.

    Set all knobs to mid position and try again. Set Sync to Auto.
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