[sdiy] Microphonics

bbob fluxmonk at gmail.com
Tue Jan 23 17:21:31 CET 2018


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

On Tue, Jan 23, 2018 at 10:25 AM, Tim Ressel <timr at circuitabbey.com> wrote:

> Interesting idea. And they're only four adult male dear at harbor Freight.
>
> --tr
>
> On 1/22/2018 11:08 PM, Miles Stevens wrote:
>
> Do you have an automotive stethoscope? I would grab one of those and probe
> around
>
> On 23 January 2018 at 09:02, Roman <modular at go2.pl> wrote:
>
>> 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.
>> A photo of the board might bring some ideas also.
>>
>> Roman
>>
>> Dnia 22 stycznia 2018 22:44 Tim Ressel <timr at circuitabbey.com>
>> napisał(a):
>>
>> Yes, it tracks vco frequency. No switchers. Power draw is low so I don't
>> think its the big electros.
>>
>> btw microphonics can go both ways. It is caused by the dielectric being
>> piezoelectric, and that can both generate and absorb sound.
>>
>> --tr
>>
>> On 1/22/2018 11:31 AM, Roman wrote:
>>
>> Is whining somehow related to VCO frequency?
>> Do you have any DC/DC converter?
>> My first guess would be the largest ceramic cap you have there.
>> Or electrolytic capacitor run over maximum ripple specs.
>>
>> Roman
>>
>>
>> Dnia 22 stycznia 2018 17:24 Tim Ressel <timr at circuitabbey.com>
>> napisał(a):
>>
>> Got a weird one...
>>
>> An oscillator I designed is whining. Well, some units do it. It is faint
>> and you have to have your ear right up against the board to hear it. But
>> an end user complained so we had to investigate. Other weirdness ensued
>> but we got the customer taken care of.
>>
>> My question is: how to find where the whine is coming from? I tried
>> using a microphone but could not pick anything up. This is an ASM-1 type
>> VCO (saw core) so there is a pulse train present. That could explain the
>> mic not picking it up. I tried putting my finger over various components
>> on the board with no luck. I thought about using an accelerometer but it
>> would have to be high sensitivity and low mass to work.
>>
>> I am at a loss.  Any thoughts?
>>
>> --
>> --Tim Ressel
>> Circuit Abbey
>> timr at circuitabbey.com
>>
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>> --
>> --Tim Ressel
>> Circuit Abbeytimr at circuitabbey.com
>>
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> --
> --Tim Ressel
> Circuit Abbeytimr at circuitabbey.com
>
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