[Elecraft] Filter TOO wide on my KX1
Don Wilhelm
w3fpr at embarqmail.com
Thu Apr 9 23:59:56 EDT 2015
Ken,
You did remember that lead "A" on the KXB3080 board connects to KX1 RF
board hole "B" did you not?
That leaves lead "B" of the KXB3080 to connect with hole "A".
Did you have good receive when you tested the installation with the
original L1 and L2 in place? Hopefully you did not skip that step. If
you had good receive at that point, then the wires of the KXB3080 board
are correct.
Most problems with the KXB3080 option come from the Low Pass Filter board.
Be certain that you have good stripping and tinning on the toroid
leads. Look at the solder side of the LPF board - if you see any
evidence of wire enamel on that side, or if any toroid lead has a ring
around it, that lead was not properly stripped and tinned.
In addition, take a look at the green lead on L2. It must route to the
rear of the board without coming in contact with L2 lead 4 on either
side of the board.
73,
Don W3FPR
On 4/9/2015 8:43 PM, Kenneth Talbott wrote:
> 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.
>>
>>
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