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<DIV><FONT face=Arial size=2>I think the earliest tempcos were a coiled length
of very fine copper wire, </FONT></DIV>
<DIV><FONT face=Arial size=2>so if they did fail, I expect the likeliest thing
would be to go open circuit,</FONT></DIV>
<DIV><FONT face=Arial size=2>which would be obvious. I don't think they would
simply drift in value.</FONT></DIV>
<DIV><FONT face=Arial size=2></FONT> </DIV>
<DIV><FONT face=Arial size=2>paul perry Melbourne Australia</FONT></DIV>
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style="PADDING-RIGHT: 0px; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; BORDER-LEFT: #000000 2px solid; MARGIN-RIGHT: 0px">
<DIV style="FONT: 10pt arial">----- Original Message ----- </DIV>
<DIV
style="BACKGROUND: #e4e4e4; FONT: 10pt arial; font-color: black"><B>From:</B>
<A title=niroke@tampabay.rr.com href="mailto:niroke@tampabay.rr.com">Nicholas
Keller</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</A> </DIV>
<DIV style="FONT: 10pt arial"><B>Sent:</B> Thursday, October 27, 2016 3:31
AM</DIV>
<DIV style="FONT: 10pt arial"><B>Subject:</B> [sdiy] Do Tempcos go bad?</DIV>
<DIV><BR></DIV>
<DIV style="DIRECTION: inherit">Strange question, probably, and I imagine all
parts can age and fail, but are tempcos generally formidable? </DIV>
<DIV style="DIRECTION: inherit"><BR></DIV>
<DIV style="DIRECTION: inherit">The reason I ask: as an SRM owner, a friend in
another state asked me to help troubleshoot his Cat SRM which is behaving in
such a way that each VCO is drifting independently (I apologize for the remote
third-party help request). He's had the PSU looked at about a year ago
or so and was told that it was stable and that the keyboard CV is also
reliable. </DIV>
<DIV style="DIRECTION: inherit"><BR></DIV>
<DIV style="DIRECTION: inherit">I had heard that the Cats used poor quality
trimmers and that often these were the cause of jumpy and unstable pitch.
However, a tech in his area who's services he cannot afford has suggested that
the tempcos are probably the culprits. Can anyone throw in some opinion
or experience so I can pass on some advice to him? Swapping out tempcos
is something he can probably handle himself, although I've warned him that
post-repair calibration could be tricky without good test equipment. Thanks
for any suggestions. </DIV>
<DIV style="DIRECTION: inherit"><BR></DIV>
<DIV style="DIRECTION: inherit"> Below are links to some pics showing the
location of the tempcos "as shown" in the schematics and "as installed" on the
VCO board, one is across the AD821 and two (both labeled R150) are across the
CA3046. Keep in mind that the schematics for the SRM do not always match
the layout diagram, and neither of those match the actual PCB :( I
suspect the "extra" R150 is actually across the AD821 and that the "real" R150
and R83 are across the 3046. </DIV>
<DIV style="DIRECTION: inherit"><BR></DIV>
<DIV style="DIRECTION: inherit"><A
href="https://imgur.com/a/3sRfG">https://imgur.com/a/3sRfG</A></DIV>
<DIV style="DIRECTION: inherit"><A
href="https://imgur.com/a/9Wsl9">https://imgur.com/a/9Wsl9</A></DIV>
<DIV style="DIRECTION: inherit"><BR></DIV>
<DIV style="DIRECTION: inherit">Thanks </DIV>
<DIV style="DIRECTION: inherit"><BR></DIV>
<DIV style="DIRECTION: inherit">Nick</DIV>
<DIV></DIV>
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