[sdiy] Newbie needs help with VCO

[Christian]

Hi

I am a newbie when it comes to VCO's, although I have been working
with electronics for over 20 years. If it isn't a 555 or a two
transistor astable, I am stumped!

I have recently (the past week) built a VCO circuit, but the darned
thing does not oscillate. I wonder if anyone could help me out.
The circuit is this one:

http://www.evenfall.com/diy/vco2061.gif

I am using a Transistor array for the Expo, and all the IC's are
socketed so I can isolate or replace them.

I have closely examined my board for errors etc three times, but all
seems well (although it isn't ).

Could someone help me out with:

a) What sort of CV do I input into the first summing OP-Amp for a
decent audiable tone for test purposes? (Middle C or 1000Hz etc?)

b) Is there a way of just making sure that the Oscillator (CA2140) is
oscillating without worrying about all the additional circuitry,
especially the EXPO and SYNC circuits.

c) I think there is an error in that circuit diagram - The Sync input
should go to the Diff-Amps non-inverting input. I believe the inputs
are the wrong way around on the LM311.

Any help is greatly appreciated.

Christian.