K1 20M / 15M Receive Problem

[Treat Hull]

Success at last.

Using the TS-50/dummy load combination as a signal source, I kept injecting
20M signal until I got signal as far as T4. The turns on T4 were correct in
number and the leads and connections looked good, but the signal stopped
there. I bit the bullet, took T4 off and re-wound it from scratch...with
extra care. When I re-installed it on the board and powered up the
set...Bingo. Immediately after I re-tuned the 15M and 20M trimmers, I was
able to receive CW, as it should be!

Thanks for all the help, otherwise I'd still be staring at the board.

Treat Hull
VA3IMO

-----Original Message-----
From: Treat Hull [mailto:[hidden email]]
Sent: September 17, 2004 9:24 PM
To: 'Tom Hammond'
Subject: RE: [Elecraft] K1 20M / 15M Receive Problem

Thanks for your advice.

If first established that the Pre-mix oscillator was truly working by using
the TS-50 as a general communications receiver.

I then went back to Cheap 'n Dirty Signal Tracing using the TS-50 as a
low-level known frequency source as you suggested below.

I believe now that the issue really affects only 20M and that 15M was just
dead.

The TS-50, pushing 10W into a dummy load, put out enough rf that I had to
move the K1 some distance away to prevent rf from getting into the earlier
stages....except on 20M where I was able to work on the K1 close to the
signal source.

When I injected a 20M signal, I had good signal strength as I worked back
through the RF Band-Pass Filter. I had good output with signal inject on the
T3 side of capacitor CJ, and next to nothing when injected on the upstream
(T4) side. Likewise, as I injected signal further upstream, the was no
output.

So the problem appears to be in the 20M RF Band-Pass Filter. Suspecting
capacitor CJ was at fault, I replaced it, but to no avail.

Any suggestions welcome!

Treat Hull

-----Original Message-----
From: Tom Hammond [mailto:[hidden email]]
Sent: September 16, 2004 8:12 AM
To: [hidden email]
Subject: Re: [Elecraft] K1 20M / 15M Receive Problem

GM Treat:

>When I found the lousy performance on 20/15, I downloaded the K1
>troubleshooting guide from the site and went through the routine for all
>bands. The receiver checked out OK for all four bands using my antenna and
>a series capacitor as a signal injector, but still no discernable CW on
>the K1 when I can hear things on the Kenwood.

The fact that you CAN receive signals on the other two bands would tend to
imply that everything in the K1 which is COMMON to all bands is (or should
be) working correctly.

This pretty much leaves only the LPF (Low-Pass Filter) and BPF (Band-Pass
Filter) is a likely culprit as they are about the only band-specific
devices... other than the Pre-Mix Board, which you stated seemed to tune
correctly... though it's still a bit suspect as a failure in the pre-mix
could also cause a two-band failure as well.

I'd suggest you try returning to Cheap 'n Dirty Signal Tracing and this
time, try using your TS-50, set to virtually NO OUTPUT power, and into a
dummyload. With luck, this will give you a very low signal level, but one
which can be used on 15/20M. If course, if those bands are open, you can
also use the signals there, but the important point is to do the tracing ON
the band when it's active with signals, or to use the TS-50 to supply a
low-level signal which won't sneak in past the part of the circuit you're
testing and which REQUIRES that you use the 'sense' antenna to get the
signal injected.

IF you use the TS-50, just wrap the insulated end of the sense antenna
around the coax of the dummyload, so a little RF is coupled into it. You
want enough RF that you can inject it thru the coupling cap while not
having so much that the sense antenna 'radiates' it throughout the K1.

If you have a receiver capable of general coverage receive (does the TS-50
meet this requirement?), with a short sense antenna stuck into its coax
connector and laid near the Pre-mix section, use the general coverage
receiver to listen for the Pre-Mix signal (22.000 MHz for 20M, and 29.000
MHz for 15M), to confirm that the Pre-mix oscillator is truly working.

Once you have confirmed that the Pre-mix osc is running, then start using
the 'signal injector' method, starting at pin 1 of P2 (P2-1), this is the
ROUND pad, and it is the OUTPUT of the BPF. Inject a signal at P2-1 and
tune the K1 around to see if you can hear the signal. If you cannot hear
the signal, then the problem probably exists in the Pre-mix since
everything PAST this point (exc. the Pre-mix) is common to all bands.

If you CAN hear the signal when injecting at P2-1, move to P2-8 (the INPUT
to the BPF) and try again. If you cannot hear the signal, or if it's weak,
try peaking the caps for that band. If the signal still doesn't peak, then
the problem's in the BPF.

If you CAN hear, and peak, signals when injecting at P2-8, move to P3-1
(output of the LPF and then to P3-8, as you did with the BPF.

>As a final check, I ran the TS-50 on low power into a dummy load and ran a
>short wire antenna on the K-1 nearby. When I tested the K-1 this way, I
>picked up the TS-50 output at the expected points on all bands, 20M and
>15M included.

This tends to imply that the Pre-Mix IS working, but it still won't hurt to
check it directly, by listening to the osc. output of the Pre-mix on a
general coverage RX, if it is available.

Good luck,

Tom Hammond    N0SS


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