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tek 2465a, again, pleeease help, cal procedure help needed desperately

Discussion in 'Electronic Repair' started by sck0006, Dec 2, 2005.

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  1. sck0006

    sck0006 Guest

    short intro
    Same problem as before, tek 2465a... In B swp, the cursor readout
    delta t reads wrong when using superimposed waveforms (using the
    single vertical line cursors reads correct). Everything else on the
    scope works fine, just the cursor readout is off in B swp. I've
    replaced many parts on the scope with the same exact outcome. I
    replaced ALL caps in the sample and hold circuit, in fact I replaced
    all caps that were that same type on all the boards. I replaced the
    delay loop with one out of a working scope (it has hv problems that we
    can't get rid of), I replaceed the ic, can't think of the number but
    it's the custom tek one that usually goes bad, still nothing (you
    know, the dip looking ic w/ the metal tab hanging out the end). I'm
    starting to wonder if it's an adjustment issue.

    So I ran through all the adjustment procedures except Cal 07. The one
    that has me wondering is in cal 1, steps 17 through 29.

    The manual says to hookup cal generator to CH1 on the IUT(instrument
    under test, of course), and also to CH1 on an additional bench scope.
    It then says to hook up B Gate out from IUT to Ch2 on bench scope.
    Ok, so far no problem. Then on bench scope, view CH1, trigger off
    CH2, both to 50ohm coupling (assuming dc?). So, you're only viewing
    CH1? It then says to put in time markers, for instance in step 17, of
    1uS. Ok, no prob. This is where I get confused.

    Step jj.
    For each step in Table 5-3 (except step 28), adjust the delta control
    for roughly the listed number of markers over the center 8 divisions,
    then superimpose markers on bench scope screen. Manually set SEC/DIV
    setting of bench scope to keep a usable time mark as listed in Table
    5-3. Use IUT DELAY POS to bring markers on screen. Some sweep speeds
    might require adjusting holdoff to see both markers. When markers are
    superimposed, press and release the trigger coupling switch. blah
    blah blah

    Ok. So from the manual, you're only viewing CH1. Ch1 is the time
    marker input from the cal generator, triggered by B gate out from the
    other scope. So, what are you superimposing. Adjusting delta adjusts
    how many marks per div. That works fine. Delay pos adjusts something
    on B gate out. I honestly don't know what to be looking for in these
    steps. Just by viewing CH1 triggered by CH2, adjusting Delay Pos will
    move the time marks left and right on the scope screen. I viewed both
    channels, and there are two pulses, looks somewhat like this,

    __ ________
    | |__| |_______

    with time marks on CH1 like:

    | | | | | | | | | | | | |

    Adjusting Delay Pos adjusts pulse width of the first pulse. I really
    don't know how to describe it. The marks will move left and right.
    just to finish up the cal, I turned the knob full ccw until no further
    movement, full cw until no further movement, and then lighed up the
    mark that was between the two marks at the two extremes with the
    rising edge of the first pulse. I performed all the steps this way,
    but I still have an offset on the cursors. I'm sure I performed this
    step wrong, and am desperately seeking help for this situation,
    because if this doesn't work, we're going to have to buy a new (or
    newer) scope.

    Has anyone performed these steps before, and if so, would you please
    tell me what I'm supposed to be looking for on this bench scope? I
    will gladly clairfy anything I can, I know this is probably not
    explained very well. Thanks very much for reading, and all comments
    always appreciated.

    Thanks, Steve
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