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Help ID'ing diodes?

Discussion in 'Electronic Basics' started by DaveC, Dec 15, 2003.

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  1. DaveC

    DaveC Guest

    Have a couple of fried glass-body diodes in what is probably an old dimmer
    circuit that I've used for years as my soldering iron variable-heat
    controller.

    Circuit consists of main pot, trim pot, diodes, choke, a few caps, and a
    3-term semi device (sort of TO-220, only smaller -- SCR?).

    The diodes have no markings save these: one has a blue stripe around exactly
    the middle of the body, and one lead where it meets the body is slightly
    flared (cathode?). The other has no markings at all on the body, save a
    barely visible black mark on one end. Both are the traditional copper color
    under the glass.

    Both measure infinite cont. in both directions.

    Presuming this was originally a 100 watt light dimmer (I'm using it to
    control a 35 watt iron), are there some generic diodes I can use as
    replacements? Can I use 1N400x here?

    The controller quit when I tried to connect my scope's ground lead to 120 vac
    (there goes another lead clip!)

    Thanks,
     
  2. DaveC

    DaveC Guest

    Scope ground lead, that is...
     
  3. Oppie

    Oppie Guest

  4. DaveC

    DaveC Guest

    How does one troubleshoot this type of device? A simple continuity test won't
    do it, it seems.

    Maybe it's not these that are at fault, at all. Maybe it's the triac? Guess
    I've gotta put those devices back in circuit, fire it up and see...

    What should I see at these device's term?

    Thanks,
     
  5. The Al Bundy

    The Al Bundy Guest

    A diac conducts at a certain voltage and current can flow in both
    directions.

    It is used to trigger the gate of the triac. This triggering is done by
    charging up a capacitor with a potentiometer. When the voltage across the
    capacitor is high enough (the spec of the diac) the diac will conduct and a
    current flows into the gate (to cathode) of the triac. The triac will then
    conduct until the sinewave of the mains goes through zero. The Triac stops
    with conducting and the capacitor charges again, etc etc.

    What you control basically is how late the triac must switch on after the
    sinewave went through zero.

    A diac you can test by putting some voltage across with a series resistor.
    This voltage has to be high enough to let the diac conduct. So just
    measuring the resistance of the diac should give high or infinitive
    readings.

    Hope this helps a bit,

    Al
     
  6. Guest

    Probably blew the triac. Try replacing it with
    whatever you have or whatever you order. There should
    be nothing critical about it, so you don't need an
    identical replacement.
     
  7. DaveC

    DaveC Guest

    The catalog I looked in (NTE) lists them by voltage (50, 100, 200, 300,
    higher) and max forward current (1A to 8A):

    http://www.nteinc.com/Web_pgs/TRIACs.html

    Do you think an NTE5629 would work, here? See something better?

    Thanks,
     
  8. One is probably a DIAC, and would normally measure infinite in both
    directions. In any case a new 300W dimmer is dirt cheap, so buy one
    and use it or the parts.
    --
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  9. Well, if you use your scope, be (again!) prepared for a surprise.

    You had better use an isolation transformer.
    --
    @@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@,@@[email protected]@[email protected],@@[email protected]@[email protected]@[email protected]@
    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  10. Guest

    It'll work fine, but it costs more than a BTA06-400. I'd
    order a few BTA06's, just to have some on hand. By the way,
    the 06 means 6 amps, and the 400 means 400 volts. You can
    get them up to 40 amps! I keep a few BTA16's on hand.
    See http://www.mouser.com/ and put triac in the search box.
     
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