[Elecraft] K2: No recieve/power out on 20M thru 10M

[W3FPR - Don Wilhelm]

Marc,

What were you using as a signal during the 'cheap and dirty signal tracing'? 
If you were using an antenna lead and off the air signals, remember that the 
bands have been rather dead the last couple days - and more so on 20 meters 
and up in the evenings.

Now that you have done the signal tracing (I assume in receive) and have 
determined that everything from D6/D7 to the audio is working, try the 
reverse using the RF probe while attempting to transmit at low power (about 
2 watts) into a dummy load.

You should see some drop in level from D6/D7 through the bandpass filters, 
but sufficient to measure.  You can easily do a comparison from band to 
band.  The output of the pre-driver stage (collector of Q5) is easy to reach 
on the top of the RF board - the collector is connected to the case.

It is true that there is nothing in common to all those bands in the 
bandpass filters.  As a totally wild guess, there might be some failure in 
the T/R switch that would convert something to a low pass filter (but that 
is a real stretch).
Could it be that your prior efforts misaligned the bandpass filters for 
those bands while attempting to align them in receive state?  You should be 
able to peak the bandpass filter during transmit (TUNE or TUNE/DISPLAY) with 
the RF probe on the collector of Q5.
If you can find any peak at all on the bandpass filters, it is likely to be 
correct and you can rule out the bandpass filter area as the problem (or 
verify that is really where the problem lies).

73,
Don W3FPR

----- Original Message ----- 
From: "Marc Glade" <mglade at gmail.com>
To: "W3FPR - Don Wilhelm" <w3fpr at arrl.net>
Cc: <elecraft at mailman.qth.net>
Sent: Thursday, November 11, 2004 2:59 AM
Subject: Re: [Elecraft] K2: No recieve/power out on 20M thru 10M


> Well, after following Tom's (N0SS) Cheap 'N Dirty Signal Tracing Guide
> it would seem that the problem does fall within the band-pass filter
> as injecting a signal at D6 works fine but at W6 hardly anything comes
> through for the aforementioned bands. Now I'm even more confused
> though as I don't see how one fault can cause issues on 20M-10M, but
> leave 30M-160M unaffected. That would leave me to believe that there
> are multiple faults in the band-pass filter which while possible,
> strikes me as very odd since everything was originally working fine
> and the now affected bands all started showing problems at the same
> time.
>
> Marc W1RSC
> K2 #4360
>
>
> On Wed, 10 Nov 2004 08:11:17 -0500, W3FPR - Don Wilhelm
> <w3fpr at earthlink.net> wrote:
>> Marc,
>>
>> There is nothing in the bandpass or lowpass filters that would cause good
>> behavior below the 10 mHz band and bad performance above that.
>>
>> I suggest that one of the few things that could cause such behavior is 
>> the
>> VCO.  Use CAL FCTR with the probe in TP1 and check the VCO frequency on
>> those bands.  The frequencies should be close to those listed in the VCO
>> Table of the K2 Schematic Key (appendix B of the manual).  Also, build 
>> the
>> RF Probe and check the VCO voltage as indicated in page 10 of the
>> Troubleshooting section (Appendix E).
>>
>> 73,
>> Don W3FPR
>>
>>
>> ----- Original Message -----
>> From: "Marc Glade" <mglade at gmail.com>
>> To: <elecraft at mailman.qth.net>
>> Sent: Wednesday, November 10, 2004 1:23 AM
>> Subject: [Elecraft] K2: No recieve/power out on 20M thru 10M
>>
>> >I am the proud owner of K2 #4360. When I first put the unit together
>> > everything checked out smoothly and there were no issues. I have since
>> > added the KSB2, KIO2, KAT2, K160RX, KNB2, K60XV, and KAF2. No issues
>> > appeared to arise after adding the modules. I had to set the K2 aside
>> > for a month due to other commitments and upon returning to it about a
>> > month ago I noticed I had no power out on any band. A quick check and
>> > replacement of R50 solved this. Except now I noticed that on 20M thru
>> > 10M with a slight exception on 15M I still had no power out and also
>> > that even with max AF gain the signal from a connected N-gen was
>> > barely perceptible. 15M is a little different in that I can get a max
>> > power out of 1.5W on that band and receive is also a little better but
>> > not by much. On 160M thru 30M the rig functions perfectly fine. I have
>> > tried re-aligning the bandpass filters multiple times to see if that
>> > was were the problem was but could not resolve the issue. I have spent
>> > hours looking over the rf board with a magnifying glass and a dmm
>> > trying to find a fault or bad solder joint but haven't found anything.
>> > My knowledge in this area is limited and I feel like I've run into a
>> > brick wall with this issue. If there is anyone that has any
>> > suggestions I eagerly await them.
>> >
>> > Thank You,
>> > Marc W1RSC
>> > K2 #4360
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