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Bridge rectifier.

Discussion in 'Electronic Repair' started by John, Oct 30, 2006.

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  1. John

    John Guest

    How do you check a bridge rectifier in circuit to be absolutely sure it
    needs replacing. Conditions: No power applied as 2amp fuse in the
    transformer primary blows immediately power is applied. Usual short circuit
    procedures followed throughout but I don't place too much reliance on this
    test . BTW, the rectifier (B40 C3200/2200)) is in a theatre organ purchased
    from an outfit no longer in business and space on the pcb is at a premium
    and discourages using single diodes.
    Thanks - John
  2. CJT

    CJT Guest

    What makes you so sure that's even possible?

    Conditions: No power applied as 2amp fuse in the
  3. Jamie

    Jamie Guest

    the primary side of the xformer could be shorted.

    to check the rectifier.
    put your DMM on ohms, place the red lead on the
    + output of the rectifier and black on the -.
    if you have a very low ohm reading, you have
    either a rectifier or a capacitor or something
    else connected to the supply shorted.
    normally, a fuse won't blow instantly unless
    it's shorted on the primary side.
    have you checked for any shorted MOV's ?

    the only way to know this, is to disconnect one
    side of the secondary and put in another fuse,
    then fire it up.
    if you don't want to use fuses, use a lamp of
    a set wattage that is near the fuse rating inplace
    of the fuse. if the circuit is still shorted badly,
    the light will glow and produce low current in your
  4. James Sweet

    James Sweet Guest

    Remove it from the board and check the individual diodes with an ohm
    meter, they're all accessible from the pins.
  5. CJT

    CJT Guest

    That's not "in circuit."
  6. zack

    zack Guest

    have you ever checked power diodes
    that thay check ok but still not work.
    ive had that also with transistors as well.
    thay can check out ok but can have
    probs when power applied.
  7. Meat Plow

    Meat Plow Guest

    Take the thing out and check it. You do know how to check a diode do you?
  8. First measure across the + and - leads of the bridge. If it's a steady
    LOW, like under 10 ohms, then it could be the bridge or anything after
    that. You'll have to cut the + lead of the bridge to isolate the
    problem any further.

    Then use an ohmmeter on its low ohm or "diode" range and measure the
    resistance across each diode, in both directions. It should be very
    different each way for each diode.

    That part is a 4-amp 100 volt bridge. The rating may have been
    marginal so I'd replace it with a somewhat heftier bridge.
  9. John

    John Guest

    Thanks for all your replies. Will proceed as advised .
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