Oscillator build problems

Discussion in 'The Projects Forum' started by JohanEricson, Aug 9, 2018.

  1. JohanEricson

    Thread Starter New Member

    Aug 30, 2017
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    Hi all!
    I've built this oscillator on a bread board, and it worked fine!
    But when i transferred it to a perf board i got a problem as you can se in the picture. And it's a pretty annoying problem since four other wave shapes is modified from this triangle wave...!

    I've read about that the jfet's on resistance can cause this, but it's the same one that was on the bread board so.. what's happening?

    Any tips?

    Thank you!
     
  2. danadak

    Well-Known Member

    Mar 10, 2018
    1,562
    323
    Looks like the trip point of U2B changed, did you swap setpoint Rs by accident ?

    Regards, Dana.
     
  3. JohanEricson

    Thread Starter New Member

    Aug 30, 2017
    27
    0
    Yeah that's what I've been wondering about that to!
    Rs?
    All of the resistors around U2B seems to be the correct value.
    Any specific resistor in the circuit you can point to?

    Thank you!
     
  4. danadak

    Well-Known Member

    Mar 10, 2018
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    R46, 47, 42,69

    Regards, Dana.
     
  5. JohanEricson

    Thread Starter New Member

    Aug 30, 2017
    27
    0
    No they all seem to be the correct value.
    But as you say it feels like there is something wrong with the triggering point..
     
  6. danadak

    Well-Known Member

    Mar 10, 2018
    1,562
    323
    Obviously the integrating cap is not being discharged long enough,
    and its clear its being switched properly in that the ramp abruptly
    changes, no tailing off or exponential discharge.

    Post a pick of ramp and comparator out, and if possible ground reference
    on scope, in relationship to waveforms.

    Regards, Dana.
     
  7. JohanEricson

    Thread Starter New Member

    Aug 30, 2017
    27
    0
    For a moment I thought I had it figured out, but as it turned out I didn't..!
    I've done some simulations trying to figure out what is going on.
    As I was messing about with I screwdriver to see if there was a connection between any of the copper rails the problem got a lot better! and I don't know why! So, for now, the problem is solved but I don't know how...
    Now the frequency range is a bit off, it goes very very low and not as high as i would like it to. So it's back to the simulation to what can be done.

    Thank you danadak for your help! I will take a picture and post!
     
  8. JohanEricson

    Thread Starter New Member

    Aug 30, 2017
    27
    0
    There is something strange going on... The frequency has increased a bit, but as the top frequency is climbing the problem is returning and getting worse.
    But no modifications have been done to the circuit.
    I have a problem with my other scope probe so I can't take the picture right now.
     
    Last edited: Aug 11, 2018
  9. danadak

    Well-Known Member

    Mar 10, 2018
    1,562
    323
    Sure sounds like a floating/loosly coupled connection, a little heat,
    a little stress and its connection integrity suffering.

    Do you have any cooling spray in a can, move over circuit section/part at a time
    and cool it to see if there is a big sensitive part/connection.

    Regards, Dana.
     
    Last edited: Aug 11, 2018
  10. JohanEricson

    Thread Starter New Member

    Aug 30, 2017
    27
    0
    Ha! It's solved!
    It was C18 that was 4,7nF instead of 4,7pF!
     
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