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Tektronix 465m - bad LV power supply?

Discussion in 'Electronic Repair' started by gabeschine, Aug 27, 2007.

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  1. gabeschine

    gabeschine Guest

    I just got a used Tek 465m. It worked perfectly when I tested it, and
    then a couple more times after that. It would then intermittently not
    turn on (although the screen illum would still work). Now, it
    consistently won't turn on (still screen illum, tho).

    I have opened it up and tested the +5/-5/+32 leads in a couple places
    on the board, and none show what they should:

    +5 = -0.11 V
    -5 = -0.05 V
    +32 = -0.04 V

    there is some, but very little, variance in the above numbers over
    time/tests.

    i'm a beginner repairing electronics, but i have the feeling this is a
    simple repair -- the thing worked perfectly until a couple days ago...
    could it be something as simple as a busted cap? i have the owners/
    maintenance manual with lots of diagrams in it (although, it seems,
    none of the power supply circuits). could anyone point me in the right
    direction to solve this problem? any help would be appreciated!
    thanks,

    gabe schine
     
  2. Jim Yanik

    Jim Yanik Guest

    well,first check to see if any internal fuses are open,the 32 unreg has a
    fuse.
    it could be bad electrolytics;they dry out with age or their ESR rises and
    the raw,unregulated supplies are not high enough for the regulators to
    work.

    TEK PS supplies all reference to one supply,and use pullups so if one
    supply dies,they all go out.

    HV multipliers are prone to fail,too;that's the black box with a heavy red
    lead that goes to the front of the CRT.

    Google for BAMA and download a service manual for the scope so you will
    have schematics to work from.
     
  3. gabeschine

    gabeschine Guest

    Thanks - got the schematics. Tested all the fuses I could find (4 of
    them) and they all check out.

    Your ref to the PS - does this mean that if the PS dies, I would see
    anything from the Scale Illum. feature? That's the only part of the
    scope that still works when power is on.

    Now I need to go and learn what everything you said means :). Thanks
    again
     
  4. Jim Yanik

    Jim Yanik Guest

    I hope you got the circuit descriptions,its VERY handy in learning about
    how your scope's circuits work.A great aid in troubleshooting.
    TEK used to write very good circuit descriptions for their instruments.Not
    anymore.
    One more thing,TEK regulated power supplies often use "foldback" current
    limiting;where when one supply gets overloaded,it *shuts down* that supply
    instead of simply limiting it's current output.
    Since that supply may be used in some of the other regulated supplies,they
    ALL drop in voltage.
     

  5. The manual can be downloaded from this site:

    http://bama.edebris.com/manuals/tek/465m/

    Circuit Descriptions should be in this file, AFAIR.

    hth,
    Andreas
     
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