<div dir="ltr">A piezo disk clamped to a dowel or rod might work. Actually, if it's a physically vibrating component, pressing on it might dampen the vibration and prevent the stethoscope for picking up anything, but that in itself might be diagnostic</div><div class="gmail_extra"><br><div class="gmail_quote">On Tue, Jan 23, 2018 at 10:25 AM, Tim Ressel <span dir="ltr"><<a href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Interesting idea. And they're only four adult male dear at harbor
Freight.</p>
<p>--tr<br>
</p>
<br>
<div class="m_2506388829699380375moz-cite-prefix">On 1/22/2018 11:08 PM, Miles Stevens
wrote:<br>
</div>
<blockquote type="cite">
<div dir="ltr">Do you have an automotive stethoscope? I would grab
one of those and probe around</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On 23 January 2018 at 09:02, Roman <span dir="ltr"><<a href="mailto:modular@go2.pl" target="_blank">modular@go2.pl</a>></span>
wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>So that narrows it down to capacitors close to VCO
core, like timing cap, decoupling caps around reset
circuit, or caps around sub-osc divider if you have one
there.<br>
</div>
<div>A photo of the board might bring some ideas also.<span class="m_2506388829699380375HOEnZb"><font color="#888888"><br>
</font></span></div>
<span class="m_2506388829699380375HOEnZb"><font color="#888888">
<div><br>
</div>
<div>Roman<br>
</div>
</font></span>
<div class="m_2506388829699380375HOEnZb">
<div class="m_2506388829699380375h5">
<div><br>
</div>
<div class="m_2506388829699380375m_2390645076341141776nh_extra">
<p>Dnia 22 stycznia 2018 22:44 Tim Ressel <<a href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a>>
napisał(a):<br>
</p>
<blockquote class="m_2506388829699380375m_2390645076341141776nh_quote" style="border-left:2px solid #999;padding-left:8px;margin:0">
<div id="m_2506388829699380375m_2390645076341141776gwp90911c5a">
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<div text="#000000" bgcolor="#FFFFFF" class="m_2506388829699380375m_2390645076341141776gwp90911c5ab">
<p>Yes, it tracks vco frequency. No switchers.
Power draw is low so I don't think its the
big electros. <br>
</p>
<p>btw microphonics can go both ways. It is
caused by the dielectric being
piezoelectric, and that can both generate
and absorb sound.<br>
</p>
<p>--tr<br>
</p>
<div><br>
</div>
<div class="m_2506388829699380375m_2390645076341141776gwp90911c5a_moz-cite-prefix">On
1/22/2018 11:31 AM, Roman wrote:<br>
</div>
<blockquote type="cite">
<div>Is whining somehow related to VCO
frequency?<br>
</div>
<div> Do you have any DC/DC converter?<br>
</div>
<div> My first guess would be the largest
ceramic cap you have there.<br>
</div>
<div> Or electrolytic capacitor run over
maximum ripple specs.<br>
</div>
<div> <br>
</div>
<div> Roman<br>
</div>
<div> <br>
</div>
<div><br>
</div>
<div class="m_2506388829699380375m_2390645076341141776gwp90911c5a_nh_extra">
<p>Dnia 22 stycznia 2018 17:24 Tim Ressel
<<a href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a>>
napisał(a):<br>
</p>
<blockquote class="m_2506388829699380375m_2390645076341141776gwp90911c5a_nh_quote" style="border-left:2px solid #999;padding-left:8px;margin:0">
<div id="m_2506388829699380375m_2390645076341141776gwp90911c5a_gwp3b3c4a3d">
<div>Got a weird one...<br>
</div>
<div><br>
</div>
<div>An oscillator I designed is
whining. Well, some units do it. It
is faint<br>
</div>
<div>and you have to have your ear
right up against the board to hear
it. But<br>
</div>
<div>an end user complained so we had
to investigate. Other weirdness
ensued<br>
</div>
<div>but we got the customer taken
care of.<br>
</div>
<div><br>
</div>
<div>My question is: how to find where
the whine is coming from? I tried<br>
</div>
<div>using a microphone but could not
pick anything up. This is an ASM-1
type<br>
</div>
<div>VCO (saw core) so there is a
pulse train present. That could
explain the<br>
</div>
<div>mic not picking it up. I tried
putting my finger over various
components<br>
</div>
<div>on the board with no luck. I
thought about using an accelerometer
but it<br>
</div>
<div>would have to be high sensitivity
and low mass to work.<br>
</div>
<div><br>
</div>
<div>I am at a loss. Any thoughts?<br>
</div>
<div><br>
</div>
<div>--<br>
</div>
<div>--Tim Ressel<br>
</div>
<div>Circuit Abbey<br>
</div>
<div><a href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a><br>
</div>
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<pre class="m_2506388829699380375m_2390645076341141776gwp90911c5a_moz-signature" cols="72">--
--Tim Ressel
Circuit Abbey
<a href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a>
</pre>
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<br>
<pre class="m_2506388829699380375moz-signature" cols="72">--
--Tim Ressel
Circuit Abbey
<a class="m_2506388829699380375moz-txt-link-abbreviated" href="mailto:timr@circuitabbey.com" target="_blank">timr@circuitabbey.com</a></pre>
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