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oscilloscope view mode or something question

Discussion in 'General Electronics Discussion' started by LordVader88, Dec 10, 2016.

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  1. LordVader88


    Dec 9, 2016
    This is a lot of words about some simple OS setting I think, but still easier than pretty girls I'd say LOL, and If I had a video I'd be 1000x easier to convey.

    I have my 1st scope, and I'm a OS newb, its a Tektronix 2430A digital 50MHz, from the 80s, off ebay, no idea its history or its actually working condition but it seems fine for the basic stuff, no idea the accuracy or noise problems etc. Its self-test passes most stuff, but fails some too that r probably why it was on ebay, but it works.

    My simple problem is just a setting thing that IDK what its called or what setting it is. And IDK if it was like it on arrival or if its something I changed. I have the manual but its a huge book.

    I can hook up a sine wave generator to ch1 and then 2, and have the same volts/div, AC/DC coupling, a few other settings all the same on each channel that I can see, and I can swap the probes and no difference for below.

    CH2 > I can look at a nice sine wave or whatever, and adjusting the CH2 vertical position up and down just moves the image up and down on the CRT screen, and the shape remains the same, the scaling, the timing...the amplitude it always the same.

    CH1 > Its like if I center the vertical position, the signal is completely flattened out to just a straight line basically, attenuated to zero basically. If I move up a bit peaks start raising up and showing (think derivatives peaks for us calculus lovers) , and more and more it will start looking like a normal sine wave again only at the top of the screen with the negative half wave shape starting to apprear. But usually never enough to see the proper full wave shape on the volts/div. By the time time I scroll up enough to get a nice sine wave, most the wave is above screen.

    And in moving down from centered screen, the 180deg reverse happens, lower peaks barely start showing from the straight line, the amplitude and shape only barely gets to sine wave shape when the signal goes off the bottom edge basically.

    If u saw it u would know exactly what I mean, my words r not the best, please help, but surely its some simple setting IDK the name off or noticed
    Last edited: Dec 10, 2016
  2. Arouse1973

    Arouse1973 Adam

    Dec 18, 2013
    Connect the probe to the calibration output, normally 1KHz pulse train which can be found on the front of the scope. what do you see?
  3. Bluejets


    Oct 5, 2014
    This might help you along a bit.....

  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    Jan 21, 2010
    The pot for vertical position on channel 1 sounds dodgy. If you can spray some isopropyl alcohol into it and sweep the control up and down several times, you may be able to improve it.

    If this doesn't completely fix it, then replacing the pot may be your next step.

    There are apparently groups dealing primarily with the repair and maintenance of Tektronix equipment. Finding one of these would be of great assistance to you.
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