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Tek 11302 behavior

Discussion in 'Electronic Repair' started by Ancient_Hacker, May 18, 2007.

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  1. I just got a Tek 11302 scope. It's in fine shape and most everything
    seems to work well.

    Except for one thing-- the main trace pulses and flashes a bit-- if
    you adjust the sweep speed just right, you can see the beam is going
    off for a few milliseconds every 20 msec or so, probably to go refresh
    all the legends on the screen.

    Now I suspect that is supposed to happen during the retrace time and
    not be quite so noticeable.

    Can anybody confirm whether this is normal or abnormal behavior?



    Thanks,

    A_H
     
  2. Normal scope behaviour. It's due to the mikroprocessor and screen/
    readout technique used during times these scope series was developed.

    hth,
    Andreas
     
  3. Jim Yanik

    Jim Yanik Guest

    I can't recall if that's the 11K model with the scope-type CRT instead of a
    video raster-scan display. The 7000 series had to interrupt the trace to
    display on-screen readouts,it did not have a raster-scan CRT display.There
    was provision to turn off the readout for non-interrupted traces in the 7K
    series.(no microprocessor in the 7K series,it was a discrete analog readout
    display,lots of TEK-made ICs.)

    IIRC,other 11K scopes had a raster-scan video display,and should not have
    to interrupt the display to show on-screen readouts.

    I have no real experience with the 11K series,just what I've observed on
    the other tech's benches.
     
  4. Okay I found the answer in the service manual.

    The scope has a "refresh priority" circuit. If you're asking for
    maximum trace performace, with no holdoff, the scope has no choice but
    to interrupt the trace to refresh the text. If there's some spare
    non-trace time, like you've dialed in some holdoff, then the text
    refreshing gets done then.

    You'd think the scope could figure out how much idle time it has after
    the sweep and before the next expected trigger. As is things flicker
    a bit more than optimum.
     
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