Very first thing if you are convinced it's built correctly is a new CA3280.
Paul S.
----- Original Message -----
From: "Jim Coursey" <dumbname@...>
To: <motm@yahoogroups.com>
Sent: Monday, December 12, 2011 12:31 AM
Subject: [motm] MOTM-190 troubleshooting
> Hi, I don't know where to direct my MOTM-2.0 build questions, since nobody
> seems to do that here, nor at e-m forums, muff, etc. Clearly Paul's
> excellent instructions must result in few gaffes, but I've managed to
> bungle one of mine at least. Let me know if you'd recommend asking
> elsewhere.
>
> I'm trying to troubleshoot VCA "A" from my MOTM-190. "B" has worked great
> for a while, and I've just been neglecting bothering to fix "A".
>
> In VCA mode, the Blend Pot works more like a mix of the 2 sources:
> CCW = Audio In, CW = CV In.
>
> In Ring mode, the Blend Pot works as follows:
> CCW = Audio In
> 12:00 = CV In
> CW = Sum of Audio In + CV In
>
> Additional weirdness: Neither TP1 nor TP2 do anything of consequence.
> (True to form, TP3 did trim out thumping as expected.)
>
> I've checked all the dumb stuff, as far as I can tell, or most of it.
> Components seem correct, with correct orientations, continuity checks
> throughout the circuit, +/-15v is at all the right IC pins, and the
> Ring/VCA switch switches between +5v and -0.2v. TP2 is adjusting the
> +/-15v to R21. Obviously I've missed something dumb, either that or a
> component is bad.
>
> I've read through Paul's description of the circuit, which is excellent
> and detailed and still partially written in Greek as far as I can tell.
> (Sorry, I'm still struggling to grasp the theory behind a lot of the
> things I'm building.) In my limited understanding it seems like something
> around the 3280 must be going wrong since "dry" audio works fine and it
> seems like CV just comes directly out of pin 13.
>
> If anyone with a better read on the workings of this module has some tips
> of components or areas of the circuit to check, I'd really appreciate it.
>
> Cheers,
> Jim
>
>
>
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