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Wall wart Transformer troubleshooting

Discussion in 'Electronic Repair' started by Taz, Sep 14, 2007.

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  1. Taz

    Taz Guest

    Newbee here. The wall wart charger for my rechargeable vacuum failed.
    It's rated 24VDC 250MA. I decided to open it up and see what's inside.
    Just a transformer, a capacitor and 4 zener diodes. Very simple
    circuit. Anyways I made an educated guess that the capacitor had
    failed, so I replaced it. Still doesn't work. I took out one of the
    diodes and checked for continuity, one way go the other no go, I
    assume it's ok and so are the rest. That only leaves the transformer,
    so my question is how do I check transformer function? Can I use an
    oscilloscope to check the transformer output? I am also wondering if a
    scope can be used to look at line voltage directly (stick the probes
    in the wall plug-hey I am just an amateur). Tnx
  2. Charles

    Charles Guest

    The diodes are rectifiers, not Zeners.

    The transformer can be checked with a multimeter.
  3. bob

    bob Guest

    If its looks like the transformer it may simply be the thermal overload
    protection which is usually mounted right on the outer windings You can get
    a replacement at radio shack check for the right temp
  4. Meat Plow

    Meat Plow Guest

    A simple voltmeter on the secondary of the transformer will tell you. Be
    careful not to make contact with the primary.
  5. hr(bob)

    hr(bob) Guest

    The thermal fuse looks like a small glass resistor in most cases, but
    will read open-circuit in both directions if it has failed. You ned
    to look at the secondary transformer voltage on the transformer side
    of the thermal fuse to be sure it is the fuse that is defective, not
    the transformer.

    Unplug the transformer and check resistances also. If you measure the
    line side resistance, it should be in the range from 10 -30 ohms, more
    or less. The secondary resistance should be about 1/5th that amount,
    as a rule of thumb.

    The diodes are probably arrnaged as a full wave bridge.

    H. R. (Bob) Hofmann
  6. Eeyore

    Eeyore Guest

    Wrong already.

    Why did you think they are ZENER diodes ?

  7. clifto

    clifto Guest

    I bought a dozen eggs the other day and the container is leaking egg.
    I took out one of the eggs and checked it for structural integrity and
    it was fine. I assume it's ok and so are the rest. So where is the leak?
  8. JW

    JW Guest

  9. clifto

    clifto Guest

    And the student was enlightened.
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