[Elecraft] K1 Audio Problem after fitting KNB1 Noise Blanker

[Don Wilhelm]

Ray,

OK since the tone dd not stop during a TUNE, that places the problem 
after transistor Q10.  Refer to the schematic for the RF board sheet 1 
in the lower left corner - everything there is suspect.
You should be able to short U4 pin 3 to ground and kill the sound - if 
that is true, the problem is with the U3, Q10 or Q11 stages and their 
associated components.  If shorting U4 pin 3 to ground does not stop it, 
it is a problem with U4 and its components.

Be aware that a leaky capacitor (in conjunction with a resistor) can 
create an unintended oscillator.  Replacement of capacitors may be in 
order - but unfortunately, I cannot tell you which ones.

As a bit of history -- at one time, the KX1 0.1 uF capacitors were a 
problem (problem now fixed), but the 0.1 uF capacitors in the K1 are not 
the same - however, if you substituted a blue body 0.1 inch lead spacing 
capacitor for a 0.1 uF capacitor used for the K1, then that is suspect.

"Tis a mystery right now - let's hope it can be found in short order.

I would re-flow the soldering at U3 and U4 just to see if a soldering 
problem is the cause.  I suspect it is - and your opening the K1 to 
install the KNB1 just accelerated an impending failure point.

73,
Don W3FPR



On 1/10/2012 4:52 PM, Ray Spreadbury wrote:
> Hi Don
> The "whine" is a steady continuous tone (perhaps at 800 or 900 cycles), not
> popping, nor a low pitched oscillation and in fact I wondered if the
> sidetone spot was on or if the key was down.
> It does vary in level with the AF gain control but doesn't change in pitch.
> It is present whether there is a signal being received or not. It is still
> present if I do a tune.
>
> 73
> Ray G3XLG
>
> -----Original Message-----
> From: Don Wilhelm [mailto:w3fpr at embarqmail.com]
> Sent: 10 January 2012 20:35
> To: Ray Spreadbury
> Cc: Elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K1 Audio Problem after fitting KNB1 Noise Blanker
>
> Ray,
>
> Please describe the "whine" in more detail.  Is it more of a "popping"
> noise, or is it a low ptched oscillation, or is it a high pitched
> squeal, or something else.
> Does it vary with the AF gain control or is it more constant - if it
> varies, does it change in level, or pitch or both?
> Does it vary when tuning through a strong signal - how about a weak one,
> or is it present whether there is a signal being received or not.
>
> If you do a TUNE (connect a dummy load first), is it silenced or is it
> still present.
>
> 73,
> Don W3FPR
>
>
>
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