transistor internally is causing fluctuating

Discussion in 'General Electronics Chat' started by Billy Mayo, Apr 11, 2013.

  1. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    if a transistor internally is causing fluctuating, what internally is wrong with the transistor? and what kind of state is the transistor in when it's fluctuating on the collectors output?
     
  2. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    How would you approach finding a bad transistor like this in a circuit?

    If a circuit is fluctuating voltage, how do you know which transistor or IC chip is fluctuating the voltage up and down or at random?

    How would a troubleshooting tech Find which transistor or IC that is cause this kind of problem?

    What is this called when a transistor or IC is fluctuating the voltage? the transistor is not shorted or open , so what is this called? or what state is the transistor or IC chip in when it's fluctuating either it's input or output?

    The Transistor is Partially Intermittent I guess you can say

    1.) The transistor is either fluctuating voltage AC or DC at the repeative pattern
    2.) The transistor is fluctuating voltage either AC or DC at a random pattern

    Using Freeze or a Heat gun on the transistor won't help troubleshoot this problem, I have tried that
     
  3. ScottWang

    Moderator

    Aug 23, 2012
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    What you said "fluctuating" is oscillation?
    Do you have the circuit and waveforms?

    The fluctuating voltage is a AC voltage, that is not a DC voltage.
     
  4. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    The Transistors is fluctuating DC voltage

    DC voltage goes on the base and it's fluctuating on the collector's output of the transistor

    What internally inside the transistor is doing this? and what state is the transistor is?

    The Transistor is not shorted or open, it called what ? when it's fluctuating?
     
  5. MrChips

    Moderator

    Oct 2, 2009
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    Suppose you replace the suspect transistor with a known working transistor.
    If you find the same symptoms then the transistor is not at fault but the entire circuit is either unstable or oscillating.
     
  6. Papabravo

    Expert

    Feb 24, 2006
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    There is nothing wrong with it. I'm pretty sure that is what they are supposed to do. How about a schematic diagram. They are worth thousands of words or so I've been told by experts.
     
  7. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    The problem is find which transistor is fluctuating, how do u a fluctuating transistor?
     
  8. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    What kind of tests or checks can i do when troubleshooting fluctuating transistors?
     
  9. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    I find that a sledge hammer or fire axe works best.
     
    #12 likes this.
  10. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    What I'm asking is when a transistor is fluctuating , I'm not talking about a circuit or a transistor in circuit, i'm just talking about the transistor by it self , when it's fluctuating

    1.) what internally is wrong inside the transistor?
    2.) What causes a transistor to get like this?

    3.) How would you know which transistors are stable and which one is fluctuating?

    I would first use a function generator and inject a .5 volts AC sine wave on the input of the base of the transistor and than see if the output is fluctuating

    How would you guys approach it to find the fluctuating transistor?
     
  11. patricktoday

    Member

    Feb 12, 2013
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    Any node of a circuit has 2 or more components attached to it by definition. How would you know that an individual transistor is responsible if the voltage is fluctuating at a particular node? It could be a reaction of multiple components working in harmony together in response to some problem condition. Transistors usually just go out completely with an open circuit or short circuit between two pins.
     
  12. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    Yes very true, so what troubleshooting skills and techniques would u use or how would u approach this?
     
  13. ScottWang

    Moderator

    Aug 23, 2012
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    There is no any fluctuating voltage will come from transistor when it is independent.

    When a independent transistor didn't adding any voltages on it, then the transistor is not a logical circuit and it also is not a amplifier circuit, there is no hfe, there is no Ib, Ic, Ie, the transistor that it is only a parts including two diodes.

    If a transistor is not a transistor and it just a parts has two diodes, then everything that you measuring is not equal to the transistor.
     
  14. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    That's True, But I have changed many transistors that was causes circuits to fluctuate or fluctuating

    The Transistor is the problem for sure, because when I change the transistor the circuit works , so it's the transistor for sure 100% only the transistor no other components around it cause the fluctuation
     
  15. patricktoday

    Member

    Feb 12, 2013
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    One test that's probably easiest is the base emitter voltage test. The base should be _about_ 0.7V above the emitter (in an NPN transistor). If the base is > 1V higher it's almost surely blown.
     
  16. patricktoday

    Member

    Feb 12, 2013
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    Are you saying that you have a particular circuit that begins to behave strangely (it "fluctuates") and you already know which particular transistor is the problem and that you have changed it many times and then, after some time passes, the same circuit begins to behave strangely again?
     
  17. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    It the base to emitter voltage always 0.7 volts? when measuring it IN circuit

    Because when I measure the base and emitter I get DC offset voltages not 0.7 volts

    How do you do the emitter to base test to get 0.7 volts? did you switch your DVM meter to diode mode or you using DC volt mode?
     
  18. Billy Mayo

    Thread Starter New Member

    Mar 24, 2013
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    No, I'm saying if you are testing 100's of the same boards and each board has 50 transistors on it and one of them is fluctuating but you don't know which one out of the 50 is doing it , how about you find it and when troubleshooting skills and techniques would you do to track the bad transistor?

    Would you start by doing what?
     
  19. patricktoday

    Member

    Feb 12, 2013
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    Yes, you do this in-circuit while it's powered on and put one probe to the emitter and one to the base in DC mode.
     
  20. patricktoday

    Member

    Feb 12, 2013
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    No idea on that.
     
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