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Tek 465M Horizontal Problem

Discussion in 'Electronic Repair' started by Ingo Cyliax, May 10, 2005.

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  1. Ingo Cyliax

    Ingo Cyliax Guest

    I have this tek 465m for many years and it has always had the
    following problem.

    There is no horizontal sweep (either A or B) when the "var" knob
    is in the calibrated position (i.e. uncal LED off). other than
    that the scope works really well and other than being an annoyance
    it hasn't bothered much.

    However, last week last week the high voltage supply when out (the
    fuse blew) and after fixing that, I wanted to dig into the horizontal
    problem. I don't think the HV problem and the clibration problem are
    related at all.

    What I have found is this.... the switch and variable pot are OK. There
    are two switch circuits, one shorts the variable potentiometer wipe to
    the low contact and the other switche the uncalibrate LED. Just shorting
    the wiper on the potentiometer using a jumper wire, while the variable
    pot is at 25% will "calibrate" the sweep timing. It turns out that the
    sweep will only work when the LED is "on". There are three LEDs which are
    driven off the same power supply, which look like they are derived from
    the +32V using a voltage divider, trigger, MAG10 and the Uncalibrate
    LED. It turns out that if either of the MAG10 or the Uncalibrate LEDs
    are on, the sweep will work. There is a small dip in the LED power
    supply rail (5mV) when either these LED are on. I suspect that this
    also effects something in the sweep generator.

    Has anyone run into this ? I do have a maintenance manual. Unfortunately,
    this manual does not have the foldout schematics and the simplified
    schematics aren't relevent. Anyone know were I can get a copy of the
    schematics for the relevent sections (i.e. sweep, LEDs, etc...).

    Thanks, -ingo
     
  2. Asimov

    Asimov Guest

    "Ingo Cyliax" bravely wrote to "All" (10 May 05 18:05:44)
    --- on the heady topic of "Tek 465M Horizontal Problem"

    Sync gate or hold off not being propagated beyond the LED logic? Trace
    back these signals and where they then end up. Seems like some logic
    input there is faulty.


    IC> From: (Ingo Cyliax)
    IC> Organization: Computer Science, Indiana University
    IC> Xref: aeinews sci.electronics.repair:47791


    IC> I have this tek 465m for many years and it has always had the
    IC> following problem.

    IC> There is no horizontal sweep (either A or B) when the "var" knob
    IC> is in the calibrated position (i.e. uncal LED off). other than
    IC> that the scope works really well and other than being an annoyance
    IC> it hasn't bothered much.

    IC> However, last week last week the high voltage supply when out (the
    IC> fuse blew) and after fixing that, I wanted to dig into the horizontal
    IC> problem. I don't think the HV problem and the clibration problem are
    IC> related at all.

    IC> What I have found is this.... the switch and variable pot are OK.
    IC> There are two switch circuits, one shorts the variable potentiometer
    IC> wipe to the low contact and the other switche the uncalibrate LED. Just
    IC> shorting the wiper on the potentiometer using a jumper wire, while the
    IC> variable pot is at 25% will "calibrate" the sweep timing. It turns out
    IC> that the sweep will only work when the LED is "on". There are three
    IC> LEDs which are driven off the same power supply, which look like they
    IC> are derived from the +32V using a voltage divider, trigger, MAG10 and
    IC> the Uncalibrate LED. It turns out that if either of the MAG10 or the
    IC> Uncalibrate LEDs are on, the sweep will work. There is a small dip in
    IC> the LED power supply rail (5mV) when either these LED are on. I suspect
    IC> that this also effects something in the sweep generator.

    IC> Has anyone run into this ? I do have a maintenance manual.
    IC> Unfortunately, this manual does not have the foldout schematics and the
    IC> simplified schematics aren't relevent. Anyone know were I can get a
    IC> copy of the schematics for the relevent sections (i.e. sweep, LEDs,
    IC> etc...).
    IC> Thanks, -ingo

    .... That was a fascinating period of time for electronics
     
  3. Ingo Cyliax

    Ingo Cyliax Guest

    thanks for the pointer...of course, the last time I worked on it,
    the -5V supplied stopped working and then the main fuse blew... so
    now I have some power supply work to do, before digging into that
    problem again...

    Later, -ingo
     
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