[Elecraft] Filter TOO wide on my KX1

[Kenneth Talbott]

Very helpful Don.  This enabled me to eliminate a large piece of realestate!
Now I am focusing on the lowpass filter and KXB3080.  Under the microscope I
discovered that wire B of the KXB3080 was never soldered!  That didn't solve
the problem but suggests there might be more issues in that area.  I will
keep looking!
Ken - ke4rg

-----Original Message-----
From: Don Wilhelm [mailto:w3fpr at embarqmail.com] 
Sent: Thursday, April 9, 2015 2:57 PM
To: Kenneth Talbott; Elecraft at mailman.qth.net
Subject: Re: [Elecraft] Filter TOO wide on my KX1

Ken,

Soldering problems on R2, RP5 or D5 and D6 can cause that problem. At one
end of rotation of R2 (the bandwidth pot) you should have near 6 volts on
the cathodes of D5 and D6, and at the other end of rotation you should have
near zero volts.
You can measure with your DMM.  I suspect you have zero volts all the time.

73,
Don W3FPR

On 4/9/2015 2:43 PM, Kenneth Talbott wrote:
> Even in the extreme counterclockwise position of the Filter pot, the 
> width is TOO wide.  A full quieting CW signal (not really strong, 
> simply above the
> noise) can be heard at diminishing volume 800 Hz above and below the 
> center frequency (1.6 kHz wide!).  This is an older KX1 which I purchased
built.
> Any suggestions as to where I should start troubleshooting?  I have 
> reviewed the assembly documentation and schematic.  At the top end of 
> resistors at pins 2 and 3 of RP5 what voltage should I expect at the
extreme ends of R2?
> Can this be measured with DMM or would I need an RF voltmeter? Thanks 
> for any suggestions.
>
>