Xpantastic!

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.
> > >
> >
>