Hi Takis, Does that mean that the DAC is faulty? Could Be, What happens if you put the old one back in, And check it's calibration, from pin 6 of U815? Karl --- In xpantastic@..., "takisdamaschis" <takisdamaschis@...> wrote:
Hi Karl,
I did the calibration procedure but unfortunately I can't get the
DAC trimmed down to 0volts!It keeps showing 4v(pin 6)!
Does that mean that the DAC is faulty?
--- In xpantastic@..., "Karl" <shire03@> wrote:
Hi Takis,
On page 34 of the Xpander service manual there is a DAC
calibrtion procedure. A different chip would need a calibration.
What about the reference voltage?
Karl
--- In xpantastic@..., "takisdamaschis"
<takisdamaschis@> wrote:
Hi Karl,
I just got the new DAC! It's an HS3140C.I installed it
and.....nothing!Every test fails now instead of only some VCO's!
My original DAC is an MP7614KN, are these two incompatible and
if so why are they mentioned as both able to do the job?
Furtermore is there anything else I should have done when I
replaced the DAC that is not mentioned in the manual?
Thanks,Takis.
--- In xpantastic@..., "Karl" <shire03@> wrote:
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@..., "takisdamaschis"
<takisdamaschis@> wrote:
Hi Karl,
the voltmeter reads 6.38v!
Takis.
--- In xpantastic@..., "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@..., "takisdamaschis"
<takisdamaschis@> wrote:
--- In xpantastic@..., "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@..., "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@..., "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@..., "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@..., "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@..., "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.
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