Xpantastic!

Hi Takis,
I measured the D805 in mine: 6.95 Vdc. I notice it's a diode in a 
transistor package. This is a very accurate reference diode. It 
should read at least 6.9 Volts. Pin 1 is not used. I measured from 
The left side of R856 ( just below it) to the middle leg of the 
diode.  My schematics identify this as a 6.9 V Zener. If the one in 
yours shows a lower voltage than that, maybe this is causing the 
tuning errors.  The diode may not be bad, something maybe dragging it 
down. I would take U815 out (turn Off first), then measure it again. 
If you can't get 6.9V out of that ref, I would replace it.  
BTW about where is the adjustment trimmer pointing?

Karl




--- In xpantastic@yahoogroups.com, "takisdamaschis" 
<takisdamaschis@...> wrote:
>
> Hi Karl,
> the voltmeter reads 6.38v!
> Takis.
> 
> --- In xpantastic@yahoogroups.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, "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.
> > > > > > > > >
> > > > > > > >
> > > > > > >
> > > > > >
> > > > >
> > > >
> > >
> >
>