I'd like to take this opportunity to thank everyone who responded.
You've all been very helpful. I probably won't be able to take
another look at this until the weekend, as I just got called in for
jury duty (selection was last week).
On 3/9/04, J. Larry Hendry put forth:
>It is also possible that the problem is in the control voltage circuit
>rather than the timing circuit. I am wondering if the CV control range
>varies greatly like the pot control range.
>
>Don't worry about the pot VR1 - variance here will make no difference.
>Here are things to check in the CV control circuit:
>R5 - controls the range of rate pot
>R6 - sets the initial frequency (summed with rate pot)
>R7 - controls the gain of the CV circuit
>R8 (tempco), R9, R10, and R11 need to be checked.
Thanks, that will give me something to think about while I'm in court :)
On 3/9/04, John Loffink put forth:
>Another possibility is a cold solder joint somewhere in the control voltage
>circuitry, including the Rate input. This will manifest itself as a high
>impedance. After building dozens of modules I finally found a cold solder
>joint in one of my VCAs. Exponential mode worked, Linear mode didn't. It
>did not take long to solve once I started probing with a meter.
Btw, my most common problem is pinched coax cables.
>Since you have two 320s, the easiest methodology is to put them side by side
>with the same control settings. Power them both on, then go through the
>schematic from the rate pot forward and compare the DC voltages at each node
>with a multimeter. If you find a large difference you will have a clue to
>the problem.
Which leads to a very important question, which module is the one
that has a problem?? They both work. Using a tuning meter, with the
knobs at "10", the one I built has a top frequency equivalent to G#
-1, but the one I bought built only goes up to A# -4 (it also doesn't
go as low).
>A problem with the timing cap seems less likely to me.
It seems very unlikely to me too. If the value were smaller or
larger than it should be, the entire frequency range would be higher
or lower. The problem I have is that the range of one 320 is much
wider than the other.