[sdiy] Do Tempcos go bad?

[Andrew Simper]

Would the oscillators drift if they differed in temperature from each
other with the tempco broken so it was an open circuit?

On 27 October 2016 at 09:09, Paul Perry <pfperry at melbpc.org.au> wrote:
> I think the earliest tempcos were a coiled length of very fine copper wire,
> so if they did fail, I expect the likeliest thing would be to go open
> circuit,
> which would be obvious. I don't think they would simply drift in value.
>
> paul perry Melbourne Australia
>
> ----- Original Message -----
> From: Nicholas Keller
> To: synth-diy
> Sent: Thursday, October 27, 2016 3:31 AM
> Subject: [sdiy] Do Tempcos go bad?
>
> Strange question, probably, and I imagine all parts can age and fail, but
> are tempcos generally formidable?
>
> 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.
>
> 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.
>
>  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.
>
> https://imgur.com/a/3sRfG
> https://imgur.com/a/9Wsl9
>
> Thanks
>
> Nick
>
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