[sdiy] my VCO not oscillating :(

[Jeff Farr]

A hot resistor is suspicous.  2N3905's are ECB IIRC.  I'm not at all
shure how the FET's should act, I would need a datasheet for the 4302
(you got one?)

Q5 touches the positive rail by way of R25, and since there is no
emitter resistor the voltage is simply a diode drop.  Q5, if I
understand things correctly, will never have a Vbe over .7v, but Vce
should be 15v when off tho.

On 12/3/05, Michael Ruberto <frankentron at hotmail.com> wrote:
> Ok, now I'm getting somewhat confused (easily done). If Q4 is seeing -3.5V
> on it's base then it should not be conducting, right?
> If that's the case why do I have +0.7V on the base of Q5?
>
> It seems to me that Q5 ought to have 15V on it's base when Q4 has a negative
> base. What gives here?
>
> M. A. Ruberto
>
>
> >From: "Michael Ruberto" <frankentron at hotmail.com>
> >To: synth-diy at dropmix.xs4all.nl
> >Subject: [sdiy] my VCO not oscillating :(
> >Date: Sat, 03 Dec 2005 13:43:24 -0500
> >
> >I have finally built the prototype of my SEM VCO clone. Unfortunately, it
> >will not oscillate. I have removed all components involved with the linear
> >detune mod and jumpered the circuit so it is the same as the original SEM
> >schematic. This was just to rule out that mod as the problem. Here's what
> >I've found so far. Q7 is conducting and is resulting in R22 getting hot
> >(not too hot). Q2 has 15 volts on it's gate. This doesn't seem right to me
> >- it seems Q2 should be conducting which in turn would hold Q7 off. I'm
> >thinking Q2 is the culprit but I'm not ruling out the possibility that I
> >have been going by the wrong pinout for the device.
> >
> >Any help with this is very much appreciated.
> >
> >
> >http://frankentron.freezope.org/source/REV4-2.gif
> >
> >M. A. Ruberto
> >
> >
>
>
>