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Scope help.. How much voltage is too much?

Discussion in 'Electronic Repair' started by Michael Kennedy, Nov 10, 2005.

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  1. I have a old heathkit tube oscilloscope. It is a model I0-17. I was wanting
    to learn a little about it and how to use it. My biggest question is how
    much voltage can a scope usually handle? This scope doesn't have any probes.
    Are there special probes for scopes that are different than those for
    multimeters?

    My first project I want to use it for is trying to find where I'm getting a
    buzz in my stereo. It will buzz if my computer is hooked up to and it is
    grounded. If the computer is ungrounded it doesn't buzz. The stereo only has
    a two wire connector so it isn't groudned. I thought this scope could be
    usefull in tracking down where the buzzing is coming from.. Anyhow I need to
    know if I can plug this thing into the wall (120vac) or if it will blow up
    if I do that.
     
  2. Ray L. Volts

    Ray L. Volts Guest

    Different strokes for different scopes. Some will only handle a few hundred
    volts before their front end will blow. Others, like Sencore analyzers, can
    handle 2000+ vdc/ac quite happily. Scope leads have important
    characteristics other than merely how much voltage they can safely handle --
    such as capacitance. Also, there are multiplier probes which allow the user
    to measure higher-than-usual voltages with the same scope.

    The manual for your scope ($22) can be found here:

    http://www.w7fg.com/manuals.php?manufacturer=Heathkit&page=5

    or here ($18):

    http://www.d8apro.com/heath2.htm

    The manual is 60 pages, btw.

    Try a device called a ground loop isolator. This may seem counterintuitive,
    since your stereo is not grounded, but isolators have been known to fix all
    sorts of seemingly weird grounding maladies. Don't be phased (pardon pun)
    by some online prices, as isolators can be had ultra cheaply; it's worth a
    shot.

    Most any scope easily accomodates 120vac, but even if the spec'd max voltage
    is well above that, it's no guarantee yours won't "blow up". Yours is
    afterall an OLD scope, which no doubt hasn't been checked for 100%
    functionality, safety and calibration in quite some time.
     
  3. tempus fugit

    tempus fugit Guest

    As for the hum, have you tried connecting bot stereo and computer to the
    same wall outlet or power bar? Sounds like ground loop to me, and if so,
    this should make it go away.
     
  4. The issue is solved by a ground loop isolator but when I run input in to my
    vcr I also get bars on the screen. I think I have a grounding issue in the
    building. The voltage spikes when the AC on the other leg of 120v starts up.
    It is not a 240v ac it is on a seperate circuit on a seperate leg. I would
    call it a sperate phaze, but it is really just off a different tap on the
    transformer on the power pole. Anyway I'm going in to too much detail. I'm
    sure you know what I mean. I think I may need to drive another grounding
    rod.
     
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