Xpantastic!

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, "takisdamaschis" 
<takisdamaschis@...> wrote:
>
> --- In xpantastic@yahoogroups.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, "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.
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>