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Tektronix 7603 scope behavior when readout board is missing

Discussion in 'Electronic Repair' started by msg, May 6, 2007.

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  1. msg

    msg Guest


    I just acquired a Tek 7603 scope with 7A18 dual-trace vert. and 7B53A
    timebase plugins but upon internal inspection and cleaning discovered
    that the readout board (when facing the front of the instrument it is
    found on the upper right side midway along the length) is missing, as
    are all interconnecting cables it uses.

    The display is very corrupted: odd blanking and sawtooth displays
    appear with no vertical input and horizontal sweep width changes with
    timebase selection in a drastic way. A vertical input signal modulates
    the strange displays in a fashion that suggests the vertical section
    is functional and the vertical position controls do work.

    The plugins are supposed to be in operating condition.

    The internal logic timeshares the display between readout and
    waveforms and is rather complex and implemented in Tek custom
    hybrid ICs and a mix of TTL and CMOS. I would really
    appreciate a report of the behavior on a working 7600 series scope
    when the readout board is disconnected; the service manual describes
    various voltage measurements with the board removed so it is
    permissible to do so and power the instrument (but no mention is
    made of the scope's behavior with the board removed).

    Many thanks to anyone willing to do this.


  2. PeterD

    PeterD Guest

    Post what options were sold as part of this scope. Some were sold
    without readouts, the fact there are no connectors indicates that
    possibly the readout option was deleted.

    IMHO, (and this is just a WAG) the problem you are reporting is not
    related to the readout...
  3. msg

    msg Guest

    Digging through Internet archives this morning I noticed a few posts
    from folks seeking the readout board for 760x scopes with a mention
    that 'Option 01' was a cost-reduced version sans this board so evidently
    the scope should work without it (if properly optioned?). I was not
    sure if any cable modifications would be needed if the board were
    removed from a scope not-so-optioned.

    And indeed I now discover an "Option 1" label on the bottom of the
    left bay so this scope never had the board.

    Its problems are elsewhere.


  4. <snippety>

    There is a Tektronix group on Yahoo groups that is loaded with very
    experienced 'Tekkies.' You would do well to take your query there.

    Off the top of my head, I would say two things.

    (1) Get the service manuals for your 'scope frame, AND both plug-
    ins. It will be nearly impossible to troubleshoot or service without

    (2) Check your power supply section for bad filter caps, correct
    voltages, noise, etc. Ironically enough, you will likely need a known-
    working 'scope to fix this one.

    Happy tweaking.
  5. Jim Yanik

    Jim Yanik Guest

    #1 check power supplies.
    the LV regulator board at the top rear of the scope had problems with the
    TO-3 connections to the PCB;the solder joints would crack and cause
    intermittents,also the DIP socket was removed and the IC soldered direct to
    the PCB. The cap-rectifier board had electrolytics go bad and cause voltage

    I used to dismantle the LV reg assy,unsolder all the 6-32 studs for the TO-
    3 xstr connections,file off the chrome plating down to the brass,and
    resolder,and they would be much more reliable.

    also,there's 4 electrolytic caps on the interface board that can cause Ps

    Then there's the "gold-dot ribbon cables" that were a cause of
    intermittents;the TEK-mod was to replace all the ribbon cables with new
    ones that did not have the "gold-dot" connectors. G-D connectors are a
    paler color than the good gold-plated connectors. Since you cannot get new
    ones anymore,you would have to rework or build new ribbon cables.( a real
  6. msg

    msg Guest

    The problem was a defective C811 (14000 uf / 25v), the -18V filter
    capacitor for the -15V supply.

    Scope works well now.


  7. tekamn

    tekamn Guest

    Sounds good to my repair eperience. Due to own experience bad/dried
    filter caps in the LV pwr supply of Tek 76xx is often a problem. I had
    more than 50 of these for repair, and most of these due to cap

    Good luck with your fresh repaired scope, it is a nice instrument
    (with and without readout option).

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