Operation confirmation please?

Discussion in 'The Projects Forum' started by Fluxor1964, Jun 3, 2017.

  1. Fluxor1964

    Thread Starter Member

    Jun 11, 2015
    ] I just built this circuit and the L.E.D glows constantly, I was expecting it to flash.....

    can someone verify please that this is supposed to be what happens before I spend time checking my wiring which
    is probably at fault since whenever I build something that doesn't work, it usually turns out to be my wiring lol

    I changed R11 to a 1K since it doesn't make sense to have 10K here.

    ignore the yellow highlight.....that was just for my reference.



    Moderator's note: The schematic is protected by copyright. The copyright owner provides the schematic on pges 25 and 26 of the instructions manual on the web page at the link below.
    Last edited by a moderator: Jun 4, 2017
  2. DickCappels


    Aug 21, 2008
    Yes is should flash. Check and see whether Q4 is oscillating or not. It is a phase shift oscillator that drives the JFET that modulates the gain of Q2.

    This circuit is only supposed to draw a few milliamps from the battery, and the LED is there to be viewed directly. Decreasing R11 may have lowered the gain of Q4 and that can be bad for oscillation. If I were troubleshooting this circuit I would use the original part values and only experiment with variations after it starts working.
    Fluxor1964 and atferrari like this.
  3. Fluxor1964

    Thread Starter Member

    Jun 11, 2015
    A phase shift oscillator, yes your right, I have never seen it drawn this way and didn't recognize it.......

    Thanks Dick.