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Identify diodes

Discussion in 'Troubleshooting and Repair' started by steinarne, Feb 8, 2016.

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  1. steinarne


    Feb 6, 2016
    Hi. I am struggling with a Toko dc dc converter that is powering a display of an old Pioneer car cassette deck.And cannot identify two diodes that are included,no markings,only colour bands on one. Has even searched all over www. Can anybody help?


    They are diam 1,8mm and length 4mm.
    Last edited by a moderator: Feb 8, 2016
  2. davenn

    davenn Moderator

    Sep 5, 2009
    HI welcome to EP

    your best bet would be getting a schematic for the unit or a full service manual
    it would be the only way to guarantee an identification

    else they are just diodes ... could be a number of different types

  3. Lightning


    Oct 12, 2013
    I have seen germanium diodes that look like that before so it would be worth finding the voltage drop.

    Diodes are pretty similar which is why we always use the ballpark figure 0.7v for the voltage drop, with the exception of germanium diodes which are around 0.3v, hence my previous statement.

    Hope this helps :)
  4. zeepee19


    Sep 16, 2009
    upperone is zener of 5.6v almost bt first u must trace pcb for that and lower one is common switching doode like 1 N 4148 or any low power scotty diode, most used in dc dc hf operation
  5. dorke


    Jun 20, 2015
    This is very hard to identify.

    The color code of the top one can be a 1N54A glass germanium diode(It may be if that thing is very very old).

    The bottom one ,who knows.

    How old is that converter?
    Are the diodes blown?
    Please post a good photo of the board ,
    indicating the location of the pulled diodes.
  6. cjdelphi


    Oct 26, 2011
    Measure the foward voltage drop, the bottom one looks like a zener (if you have an adjustable power supply, a 1k resistor and the diode in reverse, gradually increase the voltage until it begins to conduct while measuring voltage)

    Top diode? New to me, maybe it is a ge diode, measure the vdrop
  7. Lightning


    Oct 12, 2013
    Yer, if the diode is from an AC/DC converter, it could be a zener. I took apart a mains rectifier circuit the other day and found something that looks like the bottom diode.
  8. shrtrnd


    Jan 15, 2010
    Did you, as suggested by davenn, Google the model of your Pioneer to see if you can find a schematic? (I'm assuming that Toko is internal to the Pioneer(?)
    It might be helpful since I also assume you're just checking the diodes to see if they're bad or if you have another problem elsewhere.
    My experience, which may or may not be true here, is like zeepee19 noted: most of the unmarked diodes I've seen like that are 1n4148's or 1N914's.
    The physical construction of the diodes lead me to believe they're not old germaniums.
    Last edited by a moderator: Mar 3, 2016
  9. 73's de Edd

    73's de Edd

    Aug 21, 2015
    Absolutely . . . . .give us the model number of that Pioneer unit.
  10. AmidBahar


    Mar 6, 2016
    If there are no standard markings on a component it may be very difficult to determine exactly what it is without testing the component in a circuit. You may be able to guess that it is a diode or a zener diode but that does not tell you anything about its characteristics. Some manufacturers may build circuits with unmarked components purchased in bulk, and the part number can only be obtained from a schematic diagram or a parts list for the circuit.

    If you have any unknown diode you can use a voltmeter to determine the forward and reverse voltages, but if you want more detailed characteristics it can require elaborate testing.

    If you have an unknown zener diode you can use a voltmeter to verify that the forward voltage is about 0.6 or 0.7 volts. You can then connect the zener diode (in the reverse direction) in series with a 9 or 12 volt battery and a resistor to limit the current. Measure the voltage drop across the zener diode to determine the approximate zener voltage for the diode. Again this only gives you some basic information about the diode but not its type. If you need to know the exact component type you will have to consult the packaging or other information from the manufacturer.
  11. steinarne


    Feb 6, 2016
    Thank you all for your answers to my question.The green/yellow is dead. My Pioneer is an KEX900 from 1986, i have the manual, but the unit is L701 as you see, a unit on the PCB. No more schematic is available. I bought a spare converter from an Italian for 60$ and carefully dissassembled it. I ohmed the green/yellow on, and it showed 460 kohm one way, and nothing the other way (zener?) but i couldn't afford to test it, and maybe kill it.



    Last edited by a moderator: Mar 8, 2016
  12. troiuuuu


    Mar 27, 2016
    I never seen them in Viet Nam.
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