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Tektronix 465 with uncontrollable intensity

Discussion in 'Electronic Repair' started by [email protected], Oct 22, 2005.

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  1. Guest

    I've got a tek 465 oscilloscope that has a weird intensity problem. On
    powerup, the intensity gradually increases as one would normally
    expect, but it continues to rise until the whole room is illuminated
    with an eerie blue glow. The intensity knob has an effect on the trace,
    but it only goes from ridiculously bright to obnoxiously bright.

    At the point where I estimated I'd had my year's worth of x-rays, I
    turned the power off. But I think I did check a few voltages on the CRT
    circuit and didn't see anything unusual. It's been a year or so since I
    have messed with it.

    I have heard legends about CRT's shorting internally and causing this
    problem. Is this likely in my case? And how would I verify that? I did
    not observe any continuity between any of the CRT neck pins, with the
    exception of the filament, of course.
  2. Sounds like the z amp is on the fritz, but I don't know that 'scope well.
    For folks who really know their Tek. 'scopes, go to the Tekscopes group on

    It's probably something quite simple ...

  3. Jim Yanik

    Jim Yanik Guest

    The DC restorer diodes commonly are a failure item on the 465 scopes.
    They can break down under HV,but test OK on a DMM.
    If you don't have a curve tracer,just replace them.
    Next,the HV caps (in the DC restorer) themselves can break down.
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