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Tek 465 oscilloscope

Discussion in 'Electronic Repair' started by Sidney, Apr 29, 2004.

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  1. Sidney

    Sidney Guest

    Tektronix 100 Mhz dual channel oscilloscope model:Tek 465,year:1972
    one day channel 1 trace disappeared but when you press beam finder
    button the trace is on the top of the crt and while holding the beam
    finder button in and moving the channel 1 vertical position pot up &
    down the trace moves a bit but is still above on the crt screen,it is
    visible on the top but not visible when the beam finder button is
    released.I have the schematics but cannot figure it out.
    Anyone have any common repair tips?.Thanks in advance.

    Sidney
    Dartmouth,Nova Scotia
    Canada
     
  2. Sidney,
    Check the filter caps for the various low voltage supplies. I just had a similar problem but my trace
    went off the left side of the screen and that ended up being bad caps on the +5v and -8v lines. If your
    voltages are say, 2 volts or so low then you have a bad cap. If they are within say .25 volts then the trouble
    is elsewhere. Check all the caps while your at it, you have 120V (with 110v, 55v, and 22v regulated off
    that), +15V, +5V, and -8V. And make sure the schematics are for your serial number range. I was using the
    power supply schematic for an earlier version and was fruitlessly trying to find a diode that no longer
    existed.
    Filter caps seem to be the number 1 failure item in the 465s.
    Hope this helps.
    Richard WB8KRN
     
  3. Jim Yanik

    Jim Yanik Guest

    (Sidney) wrote in
    Is Ch.2 doing the same,or is it OK?
    If Ch.2 is OK,then first place I'd go is the input FET pair,look for a DC
    offset on their output. The rest of the Ch.1 preamp is differential,so you
    can pick places to short(collectors;voltage points,not current points) and
    see if the trace centers.That will narrow it down to a particular stage.

    If Ch.2 does the same as Ch.1,then the problem is in the output amp,a
    different PCB.(the one the delay line goes to.)
     
  4. TekMan

    TekMan Guest

    I'd recommnd to follow the procedure Jim suggested.
    And I would download a manual (e.g. the 475 from www.logsa.army.mil
    or the 465B from bama.sbc.edu) of one of these similar instruments
    (475/465B).

    There is a "flowcart" in each of these servicemanuals that will very
    well guide you through the process to analyze the cause of the error.

    Even if the circuits & schematics are a bit different, the flowchart
    is very well applicable to your 465.

    hth,
    Andreas
     
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