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<DIV><FONT face=Arial size=2>Make sure your Resistor values are
correct.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>I had this happen from misreading a schematic and
it took ages to figure out.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV> </DIV>
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<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=jays@aracnet.com href="mailto:jays@aracnet.com">Jay
Schwichtenberg</A> </DIV>
<DIV style="FONT: 10pt arial"><B>To:</B> <A title=synth-diy@dropmix.xs4all.nl
href="mailto:synth-diy@dropmix.xs4all.nl">synth-diy@dropmix.xs4all.nl</A>
</DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Friday, March 19, 2004 12:50
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> RE: [sdiy] VCO oscillation
problem</DIV>
<DIV><BR></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=309243505-19032004>My
4D and 4E both worked right off the bench at +/- 15V. The 4D had some
rework on the PCB I don't remember the 4E having any.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=309243505-19032004>Do a
good visual inspection and make sure all the solder joints look
good.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004>Might check the cap to see if it's the right value.
The difference between a 103 and 104 value cap is pretty
substantial.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=309243505-19032004>Also
look to what voltages the saw works at. If I remember right it should be about
0V to 1/2 +V.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=309243505-19032004>Then
it could be bad parts.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN class=309243505-19032004>It
would help a lot to if you had an oscilloscope to see what is going
on.</SPAN></FONT></DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004></SPAN></FONT> </DIV>
<DIV><FONT face=Arial color=#0000ff size=2><SPAN
class=309243505-19032004>Jay</SPAN></FONT></DIV>
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<DIV class=OutlookMessageHeader dir=ltr align=left><FONT face=Tahoma
size=2>-----Original Message-----<BR><B>From:</B>
owner-synth-diy@dropmix.xs4all.nl
[mailto:owner-synth-diy@dropmix.xs4all.nl]<B>On Behalf Of
</B>Peng<BR><B>Sent:</B> Thursday, March 18, 2004 10:33 AM<BR><B>To:</B>
synth-diy@dropmix.xs4all.nl<BR><B>Subject:</B> [sdiy] VCO oscillation
problem<BR><BR></FONT></DIV>
<DIV>
<DIV>I'm having a problem with my VCO 4E from EFM. Assembled and looks nice
but the wave outputs all produce the same high-pitched screalling. It
responds to keytracking and LFOs as cv mod. Tried the trimmers: couldn't
bring the pitch down enough. Quadruple checked pcb, wiring, solder joints,
etc. Started poking my finger around the board ( as a beginner this is my
scientic troublshooting method ) , Got to the op amp that sums the cv inputs
and touched the capacitor in its feedback loop and the pitch changed
slightly. Tried attaching a bigger cap but this had only a very small
effect. My best guess is a problem with the feedback loop. Any pointers,
suggestions, or links would be of great help.</DIV>
<DIV> </DIV>
<DIV>Thanks,</DIV>
<DIV>Peng</DIV></DIV>
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