Rhodes Chroma Polaris

I had another non-working Polaris in the shop so I swapped the chips between the 2 Polari and was able to kill two birds with one stone. I swapped out all of the chips from a polaris that doesn't boot up into the one with the channel 1 tuning problem. I did not swap the EPROMs, but I did switch all of the RAM chips around in the working one and did a full reset. The tuning problem persisted. I swapped out the DAC with a dac from a Polaris that works perfectly, and the tuning problem persisted. At this point, the only thing I have not swapped out is the EPROMs themselves. As a side benefit, I was able to confirm that all of the chips in the non working Polaris actually worked as well(except for the EPROM) and I think I am arriving at the conclusion that the EPROMs are bad in both units. Each unit has has a new 186 processor put in, and has been recapped. There's not much left to be the problem aside from perhaps a flux issue, though the board looks very clear of flux.
If anyone thinks there is something I might not have considered, please let me know. Thanks!
-Rob
--- In chromapolaris@yahoogroups.com, Rob Currier <robiecurrier@...> wrote:

>
> I'm going to pull the DAC from my OB8 to confirm that's the problem, then

I will let you know if I need one. Â More soon. Â Thanks.

> -ROb
>
>
> ________________________________
> From: synthparts <synthparts@...>
> To: chromapolaris@yahoogroups.com
> Sent: Sunday, October 2, 2011 11:47 PM
> Subject: [chromapolaris] Re: Tuning/Channel Problems?
>
>
> Â
> If you do need a new DAC I have one.
> Doug
> synthparts.com
> --- In chromapolaris@yahoogroups.com,

"John Leimseider" <leimseiderj@> wrote:

> >
> > I'd check the buffers for the 4051 first. I've also seen more than

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 the autotune. I have a couple of spares... The same ones that are in the OB8... Same symptom, sometimes.

> >
> > See if the good voices are getting really accurate octaves.
> >
> >
> >
> > John Leimseider
> >
> > Electronics Technician/ Technicien des instruments électroniques
> >
> >
> >
> >
> >
> >
> > Cantos Music Foundation/National Music Centre Project/Projet du

Centre National de Musique

> > Second Floor, 134 - 11 Ave SE, Calgary AB T2G 0X5
> > Phone/ Téléphone: (403) 543-5127
> > Fax/ Télécopie: (403) 543-5129
> > www.cantos.ca/www.nmc.ca <http://www.cantos.ca/www.nmc.ca>

<http://www.cantos.ca/www.nmc.ca <http://www.cantos.ca/www.nmc.ca>

>
> > Coming up at Cantos
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> >
> > September 25 - All That Jazz Brunch at Thomsons Restaurant
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> > A new jazz series at the Hyatt Regency Calgary. Enjoy a variety of

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>
> >
> >
> >
> >
> >
> > From: chromapolaris@yahoogroups.com

[mailto:chromapolaris@yahoogroups.com] On Behalf 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 have not figured out what

the cause is. I replaced the 4051's, swapped out CEMs from other 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 something affecting the CV coming from the DA I am guessing. Perhaps the offset calculations happening on the 4051s could be wrong? Does anyone have any ideas as to what else this might be?

> > -Rob
> >
> > --- In chromapolaris@yahoogroups.com

<mailto:chromapolaris%40yahoogroups.com> , "Paul D. DeRocco" <pderocco@> wrote:

> > >
> > > > 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 easy

> > > to find, since they're near the left end of each channel, which

are the six

> > > step-and-repeat sections on the right half of the board.
> > >
> > > This is a pretty easy thing to diagnose and fix, for anyone with

a scope and

> > > good soldering skills. You can tell if a S&H is leaking by

looking at the

> > > 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@
> > >
> >
>