Xpantastic!

Hi Tony, 
I'm talking about D805 at the DAC circuit!



--- In xpantastic@yahoogroups.com, "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@yahoogroups.com<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.
> > > > > > > > > >
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
> >  
> >
>