ASM-1 VCO testing

[Magnus Danielson]

From: "Aaron Harding" <aaharding at bigfoot.com>
Subject: Re: ASM-1 VCO testing
Date: Tue, 21 Nov 2000 21:08:01 -0500 (EST)

> Well, I'm back, with no positive results. I have checked the wiring of the
> circuit 4 times now and haven't found any mistakes. Are there any key
> points I should check? I took a few voltage measurements and thought I
> would throw them out to see if anyone saw anything strange. I am running
> +15v in on CV input one in all cases:
> 
> U1A -6.10v
> U1B -13.12v
> U2A 0v
> U2B -5.57v
> U3 -.26v
> U4 +.68v
> U5B -.26v
> Pulse Out +6.44v
> Sawtooth Out +5.56
> 
> One other thing I noticed:
> 
> My power supply puts out +14.96v and -15.06v, however, when I hook it up
> to the circuit it puts out +13.94v and -14.21v. Could this indicate a
> problem somewhere?
> 
> I have verified the pinout of the FET, as well as the 2N3904 trans. and
> all IC's. The VCO is currently outputting a constant buzz, which does not
> change with CV changes or trim pot adjustments.
> 
> Any ASM-1 guru's have any advice/suggestions?

Eh, this rings a bell. Your CA3140 is stuck at about +15V? OK, if so,
your reset constant is too short, if you would look at it with a scope
it is stuck high with small spikes down. Try bumping in some extra
capacitance there and see if you are able to make it tick. That is
what I was forced to do. I hooked extra capacitance to ground, but
that was just out of convenience.

Cheers,
Magnus