I had to change out the opto in my unit. There's a text file in the "Files"
section of the group website that has the following advice, which I
followed:
From a user (rhe solution refers to the problem of not being able to
get correct scaling of the Polysix keyboard):
I wanted to let you know that I've finally managed to repair my
Precious (Polysix). It was indeed the opto resistor, the PC-1, that
was faulty. It was suggested to me that I replace the old mysterious
PC-1 component with a VTL5C3 and change R93 from 4k7 to 1k2 (to get
the VTL5C3 working properly). I did and then the synth was as good
as new!
Appearently, the PC-1 is what stabilizes the expo-converter circuit.
If it's broken, the circuit can't manage to keep the synth in tune
as the voltages vary (which is especially noticeable during the time
the machine is warming up).
Thanks for the help!
On Tue, May 10, 2011 at 3:50 PM, ltern_te <ninonine@xs4all.nl> wrote:
>
>
> Hi Don/ Andy and thanks for your advice and feedback,
>
> Maybe a dummy question but how does one replace the P1501 with a VTL5CX ?
> Btw. did anyone find out already if its better to use a VTL5C2 or VTL5C3
> replacement?
>
> Thanks for the answer(s) in advance.
>
> Simon
>
>
> --- In PolySix@yahoogroups.com, Andrew Jury <andy@...> wrote:
> >
> > Thanks Don,
> >
> > You advice and expertise are much appreciated! I shall have a bit more of
> an
> > experiment, but I am at least ending up with the playable instrument for
> my
> > efforts rather than the sound of a piano that has been dropped out of a
> > window!
> >
> > Cheers,
> > Andy
> >
> >
> > On 27/07/2010 13:35, "longenough2002" <backshall1@...> wrote:
> >
> > >
> > >
> > >
> > >
> > >
> > > I tested this by setting VR1,2,3 to their midpoint, inserted a trimpot
> for R93
> > > and adjusted the pot for best scaling. It seemed to be about 40 point
> > > something K. 39K was the closest I had, so that's what I used. If you
> have
> > > more resistor choices (41K, 42K?) you might want to try one of those
> and see
> > > if you get better results, or even leave in a 50K trimmer.
> > > Don B.
> > >
> > > --- In PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com> ,
> Andrew
> > > Jury <andy@> wrote:
> > >> >
> > >> > Hi,
> > >> >
> > >> > Just wanted to say that I have been getting on very well with the
> > >> > Silonex / 39k resistor mod. The only problem is the tuning is a bit
> > >> > critical towards the lower end of the keyboard. Apart from that all
> is
> > >> > well and I am on my fourth successful repair.
> > >> >
> > >> > Cheers,
> > >> > Andy
> > >> >
> > >> >
> > >> >
> > >> > On 23 Jul 2010, at 16:31, "longenough2002" <backshall1@>
> > >> > wrote:
> > >> >
> > >>>> > > > Shucks, just noticed a note in the "files" section from gil_we
> > >>> > > back in Oct 2007 where he replaced the p1501 with a VTL5C3. I
> wonder
> > >>> > > if the lower temperature coefficient of the VTL5C3 makes it a
> better
> > >>> > > choice than the VTL5C2 for the tuning circuit? Some day, I gotta
> > >>> > > read the rest of the stuff in there.
> > >>> > > Don B.
> > >>> > >
> > >>> > > --- In PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com>
> , M Ll
> > >>> <f115@> wrote:
> > >>>> > > >
> > >>>> > > > Thanks for the update!
> > >>> > >
> > >>>> > > > ________________________________
> > >>>> > > > From: longenough2002 <backshall1@>
> > >>>> > > > To: PolySix@yahoogroups.com <mailto:PolySix%40yahoogroups.com
> >
> > >>>> > > > Sent: Sat, June 12, 2010 8:53:50 AM
> > >>>> > > > Subject: [PolySix] Re: Replacement for HTV P1501 photocoupler?
> > >>>> > > >
> > >>>> > > >
> > >>>> > > > Got another Polysix in the shop with tuning problems. Same
> sort of
> > >>> > > thing with octaves "stretched" and it couldn't be corrected with
> the
> > >>> > > trim pots. The diode side of the photocoupler tested bad, so it
> was
> > >>> > > time to go shopping again. This time, I thought I would try one
> of
> > >>> > > the Vactrol parts, so I got a Vactec VTL5C2 from Small Bear (same
> > >>> > > place I got the Silonex part). I replaced R93 with 22K (up from
> > >>> > > 4.7K) and it seems to be working very well, so now we have a
> couple
> > >>> > > of choices for replacing the P1501.
> > >>>> > > >
> > >>>> > > > Don B.
> > >>>> > > >
> > >>>> > > >
> > >>> > >
> > >>> > >
> > >> >
> > >> >
> > >> > [Non-text portions of this message have been removed]
> > >> >
> > >
> > >
> > >
> > >
> > >
> >
> >
> >
> > [Non-text portions of this message have been removed]
> >
>
>
>
[Non-text portions of this message have been removed]