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ID a motorola diode

Discussion in 'General Electronics Discussion' started by Doug3004, May 3, 2017.

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  1. Doug3004


    Sep 5, 2014
    I bought a grab-bag of NOS resistors and there was a diode thrown in. Just out of curiosity I'm trying to ID it.

    It is definitely a Motorola diode. The labeling is clear and complete, it has the Motorola "M" clearly printed on it, and there's pictures of other similar diodes in Google if you search there for 'tiny Motorola diode'.
    My mega328 parts tester says it's a diode: Uf = 767mv and C = 139pf.
    It is a thru-hole part and the body is pretty small, maybe 1.5mm x 3mm, with thin leads, maybe 26ga.
    Since the resistors are NOS carbon-composition, the diode may be older as well. It may be discontinued or superseded by another part# now.

    The labeling is horizontal around the diode body and reads as follows:
    MK (the M is the Motorola M logo inside a circle)

    On some other diodes the first number indicates the general series of the diode, as in this page-
    But that doesn't work here. If I google for "motorola diode 57" I just get page 57 of the Motorola catalog, or page 57 of other electronics parts catalogs.

    I have diode assortments around with all the common stuff, I don't need it for anything so it's not really critical. I'm more curious about how to go about researching this stuff.

    I would assume if you could read the markings and the part wasn't ancient, that finding info would be easy--but I can't get nuthin here?
  2. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Sir Doug3004 . . . . .

    I've seen one or two diodes . . . . . and those cryptic numbers mean nothing to me , 0ther than the 57 58 numbers tying well into the hey-day of carbon composition resistors.
    The 767 mv Vf spec tells us that you have a silicon diode.
    In those days even our workhouse 1N914 and current 1N4148 switching diodes had not made the scene.
    BUT you might pull out one of those and see how it compares on the capacitance reading.
    It you have an adjustable high voltage supply of up to a kilovolt at hardly no current demand at all . . . .in the microamperes.
    You might then non destructively test the diode for its peak voltage break down .
    You do this by using a DVM with that range capability and then connecting the output of the supply to a 1 meg series current resistor and then the meter gets connected outwardly past that resistor to keep a monitoring on the voltage level.
    You have the anode of the MYSTERY diode to ground thru a clip lead. that then leaves the cathode lead free.
    You start bringing up the supply voltage up from an initial 0 on up to ~ 50 V.
    you then touch the diode to that 1 meg plus the meter probe junction to initially see if you might have yourself a Zener diode.
    If the voltage does not decrease, then pull the diode away and step up the voltage ~ 50 V more and retest again.
    You keep upping the voltage until there is some level where you see the touching of the diode making an ever so slight decline in the initially measured voltage, that is your junction breakdown threshold.
    Deduct 50 volts and that will be your diodes HV break down spec.
    I can spec a diodes current also but that requires a 1- 5A regulated constant current source..
    Go ye forth and see what you have found yourself . . . . . cause I think that your cryptic set of numbers will help you NONE ..

    73's de Edd
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