Xpantastic!

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.
> > > >
> > >
> >
>