Transistors - faked or failed ones?

Discussion in 'General Electronics Chat' started by atferrari, May 26, 2012.

  1. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
    There is a lot of 40 transistors marked as:
    C K7A
    (no logo

    I spent part of the morning matching them in pairs of similar Vbe for a constant current.They were all tested diode-connected (collector to base). No news here.

    When trying to measure Ic for a constant Ib of 0,107 mA, found that no matter what Vb I applied to Rb (or leaving in the air), Ic was a steady 34 mA and transistor was rather warm.

    After two hours checking everything, and contradicting what the datasheet shows, I reversed the pins (easy because base is the middle pin) and everything started to be "normal" with an Ic of 25 mA only when +9 V was applied to the base resistor. Otherwise, Ic = 0 mA.

    Recalling that my DMM has hFE measurements, I got some credible value of 210 appr only when reversing the pins as above.

    Further tests with a LED confirmed that something is going wrong: in the datasheet condtion, if I apply +9V to Rb and then leave it in the air, the LED stays dimly ON.

    Reversing pins, LED switches ON and OFF as expected.

    Last tests I did just for few of them. I had enough for he day.

    Faked or failed ones sent to market expecting an idiot like me buying them?
    Last edited: May 26, 2012
  2. KL7AJ

    Senior Member

    Nov 4, 2008
    I suspect that the pinouts may be different. Even transistors with the same part numbers can have different pin orders.

  3. bertus


    Apr 5, 2008
  4. Wendy


    Mar 24, 2008
    I have one lot of faked PN2222 I bought a long while ago. It was still a good deal, the other 19 lots of different transistor (Qty 1000/lot) were good, and I paid a pittance for 20000 transistors. I suspect these were fall outs. Given the base price was something like $10 I didn't hold it against them.

    BG Micro sells a lot of Mfg marked PN2222 for 1000/$4 if you are ever interested.
  5. atferrari

    Thread Starter AAC Fanatic!

    Jan 6, 2004
    Gracias Bill and to all that replied.

    It seems they had just the pins reversed because a detailed test show they are working OK. :) :) :)

    After so many years of RTFM I trusted the 6 or 7 datasheets I looked for first. This time, it did not help and that is why I believed they were faulty (or faked).

    BTW, those 4 USD, is a third of what I paid for the lot of 40 locally. Such is life...

    Soldering now.