Xpantastic!

Hi,
are you talking about the D805 diode?
If so, mine does not have a capacitor parallel to it!
Did yours have one all along? If so please let me know of it's specs
so that I can add one myself!
Thanks!

 
--- In xpantastic@yahoogroups.com, "bjorn roland" <bjorn.roland@...>
wrote:
>
> Tip...
> A zener diode is always "noisy". It generates ripples in the voltage.
> Ripples in referance voltage may cause autotune to fail.
> To avoid these ripples there is always a capacitor mounted in
paralell to
> the zener
> to flatten out these ripples. Check ac voltage also, not only dc.
> Ac will show ripples. Should be zero, but if not check out this
capacitor.
> 
> On Thu, Oct 2, 2008 at 5:02 PM, Tony Cappellini <cappy2112@...> wrote:
> 
> >    Hello Takis
> >
> > Where did you make the measurement?
> > This sounds somewhat like the reading I got- when I measured one
of the
> > diodes near the battery. (as directed in the service manual test
procedure)
> >
> >
> >
> > On Thu, Oct 2, 2008 at 1:12 AM, takisdamaschis
<takisdamaschis@...>wrote:
> >
> >>   Hi Karl,
> >> the voltmeter reads 6.38v!
> >>
> >> Takis.
> >>
> >> --- In xpantastic@yahoogroups.com <xpantastic%40yahoogroups.com>,
"Karl"
> >> <shire03@> wrote:
> >> >
> >> > Hi Takis,
> >> >
> >> > What does the your voltmeter read when you measure the zener(D805)?
> >> > I keep thinking it's something to do with this circuit.
> >> > I am going to open mine up and see what I get.
> >> >
> >> > Karl
> >> >
> >> >
> >> >
> >> > --- In xpantastic@yahoogroups.com <xpantastic%40yahoogroups.com>,
> >> "takisdamaschis"
> >> > <takisdamaschis@> wrote:
> >> > >
> >> > > --- In xpantastic@yahoogroups.com <xpantastic%40yahoogroups.com>,
> >> "Karl" <shire03@> wrote:
> >> > > >
> >> > > Hi Karl,
> >> > > done everything you pointed out,no improvements!
> >> > > Anything else you can think of before we go for the DAC?
> >> > > Thanks,Takis.
> >> > >
> >> > >
> >> > > > Hi Takis,
> >> > > > > I also noticed that I get 3.79V at one of the pins of U815
> >> > instead
> >> > > > > of 4.0V(+/- .05V) as the service manual points out!
> >> > > >
> >> > > > Okay, lets look at D805, A zener diode which provides the
> >> > reference
> >> > > > for the DAC.Measure this with a good voltmeter, it should be
> >> > 6.9V.
> >> > > > Again, try reflowing the solder around this part and the ref
> >> > circuit.
> >> > > > If you have a service
> >> > > > manual, Look at the circuit around U815 and reflow all the
solder
> >> > > > around this part and the resistors capacitors etc...
> >> > > > Try this and let me know.
> >> > > >
> >> > > > Karl
> >> > > >
> >> > > >
> >> > > >
> >> > > > --- In xpantastic@yahoogroups.com
<xpantastic%40yahoogroups.com>,
> >> "takisdamaschis"
> >> > > > <takisdamaschis@> wrote:
> >> > > > >
> >> > > > > Hi Karl,
> >> > > > > I have gone and replaced all parts you suggested,
re-seated the
> >> > dac
> >> > > > > and went over all solders!
> >> > > > > No improvement, I keep getting the same problem!
> >> > > > > I also noticed that I get 3.79V at one of the pins of U815
> >> > instead
> >> > > > of
> >> > > > > 4.0V(+/- .05V) as the service manual points out!
> >> > > > > Anyway the good news is that I found a NOS dac ($150) which I
> >> > will
> >> > > > try
> >> > > > > out as soon as it gets in(in a few days I hope).
> >> > > > > I'll let you know!
> >> > > > > Thanks,Takis.
> >> > > > >
> >> > > > >
> >> > > > > --- In xpantastic@yahoogroups.com
<xpantastic%40yahoogroups.com>,
> >> "Karl" <shire03@> wrote:
> >> > > > > >
> >> > > > > > Hi Takis,
> >> > > > > > The other caps are Cx33 and Cx37 with x being
2,3,4,5,6,7 for
> >> > > > each
> >> > > > > > voice respectivly. And Yes they are the same 2.2uF 50V Make
> >> > sure
> >> > > > they
> >> > > > > > are 50V rating. and correct polarity (You probobly knew
that)
> >> > > > > > But before you replace those, try this.You are saying
you are
> >> > > > having
> >> > > > > > problems with all the voices right?
> >> > > > > > This points to the main DAC/Tuming circuit as you have
> >> > already
> >> > > > > > guessed.
> >> > > > > >
> >> > > > > > I would look closely at:
> >> > > > > > U811 The DAC
> >> > > > > > U816,U805 Multiplexer 4051
> >> > > > > > U812,U815,U813 Op Amps TLO81,TLO84,TLO81
> >> > > > > > U814 Analog Switch 4053
> >> > > > > >
> >> > > > > > Any of these parts failing could cause tuning problems like
> >> > you
> >> > > > > > describe.
> >> > > > > > Now, before you replace them carfully pull them from the
> >> > sockets
> >> > > > and
> >> > > > > > re-seat them. Sometimes corrosion on the socket/chip
lead can
> >> > > > cause
> >> > > > > > a "not to good" connection. Also before I replaced them I
> >> > would
> >> > > > > > reflow the solder on the bottom of the board, as bad solder
> >> > > > joints
> >> > > > > > could also cause this.
> >> > > > > > If this does not work replace em. All except the DAC are
> >> > readily
> >> > > > > > available. I would wait till you replaced the other chips
> >> > before
> >> > > > you
> >> > > > > > went searching for this DAC to see if any others are the
> >> > cause.
> >> > > > If
> >> > > > > > one of the chips have failed, I would bet on the mux or
> >> > analog
> >> > > > switch.
> >> > > > > > It would not hurt to replace the capacitors I mentioned
> >> > above, as
> >> > > > > > they are probobly on their way out anyway.
> >> > > > > >
> >> > > > > > Let Me Know How It Goes
> >> > > > > >
> >> > > > > > Karl
> >> > > > > >
> >> > > > > >
> >> > > > > > --- In
xpantastic@yahoogroups.com<xpantastic%40yahoogroups.com>,
> >> "takisdamaschis"
> >> > > > > > <takisdamaschis@> wrote:
> >> > > > > > >
> >> > > > > > > Hi Carl,
> >> > > > > > > yes I replaced all six Cx49 capacitors!
> >> > > > > > > What number are the other ones you're refering to?Are
they
> >> > also
> >> > > > > > 2.2uF?
> >> > > > > > > Many thanks,Takis.
> >> > > > > > >
> >> > > > > > >
> >> > > > > > > --- In
xpantastic@yahoogroups.com<xpantastic%40yahoogroups.com>,
> >> "Karl" <shire03@> wrote:
> >> > > > > > > >
> >> > > > > > > > Hello takisdamaschis,
> >> > > > > > > >
> >> > > > > > > > When you say output capacitors, are you talking
about the
> >> > > > small
> >> > > > > > 2.2uF
> >> > > > > > > > Cx49 at the edge of the voice board? There is one for
> >> > each
> >> > > > voice.
> >> > > > > > > > There is also one of these at the output of each VCO
> >> > feeding
> >> > > > the
> >> > > > > > VCF
> >> > > > > > > > If these go you can have tuning problems. Also, try
> >> > resetting
> >> > > > the
> >> > > > > > > > software.( hold sown clear and turn power On)
> >> > > > > > > >
> >> > > > > > > > Karl
> >> > > > > > > >
> >> > > > > > > >
> >> > > > > > > > --- In
xpantastic@...m<xpantastic%40yahoogroups.com>,
> >> "takisdamaschis"
> >> > > > > > > > <takisdamaschis@> wrote:
> >> > > > > > > > >
> >> > > > > > > > > Hi everyone, my xpander seems to fail the VCO
tune test
> >> > > > > > randomly!some
> >> > > > > > > > > voices fail during one test and pass on the next!
there
> >> > is
> >> > > > no
> >> > > > > > > > > cosistancy on the voices that fail,it can be any
one of
> >> > > > them!
> >> > > > > > Some
> >> > > > > > > > > times(rarely) the vco test passes! I have the same
> >> > problem
> >> > > > > > sometimes
> >> > > > > > > > > with the Resonance and VCF but not as often!
> >> > > > > > > > > I have totally rebuilt the power supply,changed the
> >> > battery
> >> > > > and
> >> > > > > > output
> >> > > > > > > > > bypass capacitors!All currents measure right so
this is
> >> > not
> >> > > > a
> >> > > > > > voltage
> >> > > > > > > > > supply problem!
> >> > > > > > > > > The only other part I can think of is the DAC or
maybe
> >> > the
> >> > > > > > Timer?
> >> > > > > > > > > Any thoughts?
> >> > > > > > > > > Takis.
> >> > > > > > > > >
> >> > > > > > > >
> >> > > > > > >
> >> > > > > >
> >> > > > >
> >> > > >
> >> > >
> >> >
> >>
> >>
> > 
> >
>