[sdiy] my VCO not oscillating :(

[Michael Ruberto]

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
>
>