op amp query no output

Discussion in 'The Projects Forum' started by dougalere, Sep 11, 2016.

  1. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    hi
    hi ive been getting some help on more general points on this system,over on tech repair , for which im very grateful,
    but i thought i,d give them a break, as this is a bit more straightforward and specific.

    i have an op amp in circuit , it is reading. 4.1 volts on the inverting input.
    4.37 volts on the non inverting input
    and .zero volts on the output

    thats with + 15.13 volts on the pos power supply pin and 14.3 volts 0n the neg power supply pin.

    as its in a tricky place to get to, could someone please be kind enough to confirm that the op amp is faulty.
    thank you.
     
  2. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,935
    383
    I presume you mean -14.3V on the negative supply pin.
    Either the amp is faulty or the connections or usage are incorrect in some way.
    Which op-amp are you using?
     
  3. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    hi
    the op amp is the dual njm4580

    forgot to mention --all voltages and signal voltages are dc,
    and output not connected.

    yes
     
    Last edited: Sep 11, 2016
  4. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,935
    383
    The supply and input voltages are appropriate for this amplifier so we are back to a faulty chip or your connections to it. Check the pin connections in the datasheet for the particular package that you have and compare with your circuit. Check that your output is not short-circuited to ground.
     
  5. #12

    Expert

    Nov 30, 2010
    16,283
    6,795
    A good op-amp in a defective circuit, the output usually sticks to one of the rails. That is, the output is stuck either to the highest or lowest voltage available. The exception is when they are oscillating. That makes most DC meters go a little crazy.

    Check for oscillation. If it's all nice, clean DC, I'd say replace the chip. If the output is still wrong, then I was wrong.
     
  6. dannyf

    Well-Known Member

    Sep 13, 2015
    1,792
    360
    what does "no output" mean?
     
  7. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,935
    383
    TS said the output was 0V.
     
  8. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    solved
    put a new op amp in -working fine,
    thank you
     
  9. AlbertHall

    Well-Known Member

    Jun 4, 2014
    1,935
    383
    Triffic :)
     
  10. dougalere

    Thread Starter Member

    Mar 4, 2015
    128
    5
    solved.
    changed opamp ,
    good output now,
    thank you
     
    absf likes this.
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