I’d check the buffers for the 4051 first. I’ve also seen morethan the normal failure of the DACs. When they lose a really low order bit,certain voices won’t tune, just a matter of what voltages are needed for theautotune. I have a couple of spares… The same ones that are in the OB8… Samesymptom, sometimes.
See if the good voices are getting really accurate octaves.
John Leimseider
Electronics Technician/ Technicien desinstruments électroniques
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Coming up at Cantos
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The Lions aren’t showing signs of slowing down! The finalCalgary gig of the year is at Cantos for a double album release and doing goodby helping with an instrument drive for The Legacy Children’s Foundation.8:00pm, tickets available online.
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A new jazz series at the Hyatt Regency Calgary. Enjoy a variety ofdynamic jazz perfomances the last Sunday of the month for the All That JazzBrunch. The John Gray Trio performsat Thomsons Restaurant. 11:00am.
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From:chromapolaris@yahoogroups.com [mailto:chromapolaris@yahoogroups.com] OnBehalf Of rob
Sent: Thursday, September 29, 2011 4:39 PM
To: chromapolaris@yahoogroups.com
Subject: [chromapolaris] Re: Tuning/Channel Problems?
I experienced this issue as well. I still havenot figured out what the cause is. I replaced the 4051's, swapped out CEMs fromother voices, replaced the electrolytics, and still cannot make voice one tune.It seems to be happening to both oscillators on voice 1, so this is somethingaffecting the CV coming from the DA I am guessing. Perhaps the offsetcalculations happening on the 4051s could be wrong? Does anyone have any ideasas to what else this might be?
-Rob
--- In chromapolaris@yahoogroups.com,"Paul D. DeRocco" <pderocco@...> wrote:
>easy
> > From: charlespjackson
> >
> > Recently I began to experience an issue with my Polaris going out
> > of tune. Upon doing some research and reviewing older posts here
> > regarding similar problems it appears that the culprit has been
> > narrowed down to a faulty Channel (1). If I manually disable
> > this channel then the Polaris functions and stays in tune just fine.
> > From what I've gathered so far it seems the problem might be some
> > bleeding and/or bad (Sample & Hold) caps?
> > I would just like to know if I'm accurately diagnosing the
> > problem and if so how intricate/expensive a fix this may be? Are
> > the parts necessary for such a fix available? Where might I be
> > able to locate them?
>
> I think it's usually the 4051 analog switches that leak. They're pretty
> to find, since they're near the left end of each channel, which are thesix
> step-and-repeat sections on the right half of the board.and
>
> This is a pretty easy thing to diagnose and fix, for anyone with a scope
> good soldering skills. You can tell if a S&H is leaking by looking atthe
> op-amp outputs (pins 1, 7, 8 and 14 of the nearby TL084/LF347 parts) and
> seeing if there's any sawtooth modulation larger than a few millivolts.
>
> --
>
> Ciao, Paul D. DeRocco
> Paul mailto:pderocco@...
>