Xpantastic!

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, "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, "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, "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, "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, "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.
> > > > >
> > > >
> > >
> >
>