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Diode identification?

Discussion in 'Electronic Components' started by John E., Mar 2, 2007.

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  1. John E.

    John E. Guest

    It's shorted, burned on the side against the board, the side of the diode
    that has part of the p/n printed (of course)...

    Best I can make out is (reading around the diode:

    Physically it resembles a typical 1A black epoxy rectifier.

    Would this be 1n4147? The "47" is clearly visible, and I think I can make out
    a "4" in the first part of the poorly-legible digits. No telling how many
    digits between the two "4"s.

    Any possibilities other than 4147?

  2. Palindrome

    Palindrome Guest

    Not wishing to trach granny, but this would be my approach:

    Reverse engineer parts of the associated circuitry until I am reasonably
    confident of what sort of application it is being used for, eg lf
    rectifier, hs switch, flywheel, etc. Or more importantly, if it is a
    zener.. It is normally not to difficult to work out what the diode is
    doing and what sort of currents, voltages and frequencies are happening
    to it.

    At that point, wire in an external diode with a much, much higher spec
    than the original - and measure the actual running parameters. I keep a
    few huge and very expensive semiconductors just for this.

    Then match a diode to that requirement, by measuring what is actually
    happening - with any luck the spec will match to something with a lot of
    4s and the odd 7 in its product name.

    Assumptions about what things may be tend to bite..
  3. Genome

    Genome Guest

    Unfortunately a 1N4147 is a small signal glass diode.......

    I would take a guess that what you have got is a zener diode.

    Try googling for a 1N4747.

    If it's fucked then something else might have fucked it so check the rest of
    the circuit. However it sounds like it might have been slowly fucked so you
    might want to re-design the circuit.

  4. John E.

    John E. Guest

    Ah, another ITT diode on the board starts with "ZY" (where "Z" could be
    mistaken for a "4" on the charred carcass). So I looked up ZY47 and get a
    4.7v power zener diode, 2W.

    Also, according to a National data sheet I found, a 1N4147 (a.k.a. 1N914A) is
    glass, and way too lightweight physically compared to my charred sample.
    Wrong turn, I think.

    So it looks like ZY47?
  5. Ben Miller

    Ben Miller Guest

    You can't just guess at this. As sue suggested, you need to look at the
    circuitry and figure out what that diode function is. What is the circuit
    for? What components are near the diode? Can you trace the diode connections
    to the next devices? What are they? Once that is determined, there are
    likely substitute devices that will work just fine, even if you can't
    identify the original. I do this all the time as I restore a lot of old test
    equipment. It can be a challenge when you don't have the schematic, but
    generally you can get there with enough patience and logical thinking.

    Ben Miller
  6. John E.

    John E. Guest

    Ben Miller sez:
    OK, here goes:
    German-made paper-handling machine, c. 1989. Circuit activates solenoid,
    taking several inputs from other sensors, signals, etc.

    Anode of unknown diode is to ground, cathode to drain of BUZ72 MOSFET. 1uF
    cap also from drain to ground. Drain connects to solenoid. Drive voltage is

  7. Arfa Daily

    Arfa Daily Guest

    Not then, I would suggest, a 4.7v zener ... Sounds like it's just a
    flywheeling diode and a 1N4007 would do the job just fine. Does the FET
    source go to ground ? Many power MOSFETS have a diode internally in that
    orientation across from the source to the drain. It gets there as an
    integral side effect of the manufacturing process.

  8. Dave Platt

    Dave Platt Guest

    flywheeling diode and a 1N4007 would do the job just fine. Does the FET
    Newer designs seem to use a fast-recovery diode (e.g. FRED or HEXFRED
    or HiperFRED) for MOSFET flyback protection. 1N4007s aren't
    particularly fast, and reverse-conduction losses can be significant if
    the switching frequency is high (in e.g. an SMPS). That's probably not
    all that much of an issue in a solenoid driver, though.
  9. I hope it doesn't come to that, if she has any breathing difficulties at
    all, I imaging it's just due to the rarified air of this place.
  10. Ben Miller

    Ben Miller Guest

    Anode of unknown diode is to ground, cathode to drain of BUZ72 MOSFET. 1uF
    The diode is a snubber to bypass the inductive kick from the solenoid when
    it deenergizes. A 1N4007 will work fine.

    Ben Miller
  11. Eeyore

    Eeyore Guest

    That's not what either a 1N4147 or 1N4447 looks like.

  12. Eeyore

    Eeyore Guest


    2 watt zener 47V ? The number after the C is the voltage. 4.7 volts would be
    BZY47-C4V7 btw.

  13. Franc Zabkar

    Franc Zabkar Guest

    Go here ...$$Search?OpenForm

    .... and type the following into the search box:


    - Franc Zabkar
  14. Arfa Daily

    Arfa Daily Guest

    That was my thought, and the reason that I suggested a KISS approach with a

  15. John E.

    John E. Guest

    Arfa Daily sez:
    The source connects to a flame-resistant (blue), less-than 1-ohm, 1/4w(?)
    resistor (red-violet-gold-gold) that measures about 0.5 ohm. (It should
    measure 0.27, yes? Maybe candidate for replacement? But maybe it's my Fluke
    77's accuracy at that low setting. Resistor doesn't look abused...) The other
    end of the resistor does connect to ground.
    Yes, I've read about the need to short out back-EMF when dealing with relay
    coils, solenoids, etc.

    So, 1N4007 it is.

    An after thought... since the diode was cooked (it actually charred the PCB
    beneath it) but the resistor and the FET are OK, maybe the diode needs to be
    boosted to a higher A rating? Thoughts?

    Thanks to all,
  16. Werty

    Werty Guest

    Black ? What size ? I guess 1n4007

    1KV , ?1amp , 40 amp surge

  17. Eeyore

    Eeyore Guest

    It seems my post aboutt his didn't reach the group.

    It's most likely a BZY47-C47 2 watt zener 47V

  18. Eeyore

    Eeyore Guest

    You would be wrong.
  19. YD

    YD Guest

    Late at night, by candle light, Eeyore
    Spot-on I think. It'll normally have 42 V across it, not enough to
    conduct. When de-energizing there'll be a spike wich it clamps at 47
    V. Dunno why the 1 uF cap.

    - YD.
  20. Eeyore

    Eeyore Guest

    German overkill engineering !

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