K1-2 No TX on one band

[Detrick Merz]

Folks,

I built my K1 around the end of last year (my favourite xmas
present!).  Originally I had a 2 band module with 80/15 on it.  A few
months later, I bought a second 2 bander, with 40/30.  The 40/30 works
fine on both bands, but I can't get 15 to play nice on the 80/15
module!

Originally, I thought my troubles were due to a poorly matched
antenna.  The KAT1 just wouldn't get anything better than 9.9 on 15M.
I was okay with this, figuring it was just my bad luck in having a
poor length of wire up (80 matched beautifully, as did 30.. but both
40 and 15 were no good).  This weekend, I put up a G5RV, about 80-90'
up in some trees.  Of course, I had to try the new antenna, and see
how the thing worked... at least if I could match up on more bands
now.  80, 40 and 30 matched up just fine.  15 still shows  9.9 when
the KAT1 tries to work it's magic.  Now, I'm still new to all of this
HAM stuff, but, the G5RV is supposed to match up on 15, right?  I
mean, at least better than 9.9:1!

So, I've begun to suspect that there's something buggy in the 15M
section of this filter board.  I did peak the filters, although even
if they were *very* far off, I would still expect *something* better
than  9.9:1 (but maybe this is my ignorance).  I figure it being on
the filter board, and not on the RF board because:

1) 80M (band 1, board 1) works fine
2) 30M and 40M (band 1 & band 2, board 2) both work fine (this kind
rules out the RF board, I think, since the RF board is talking to both
bands on the second filter board just fine).

So, thinking there might be trouble in band-2 land on this 80/15
filter board, I've gone and done the investigating that I know how to
do.  I've turned up nothing, so I come to the rest of you for some
help.  Here's what I've done:

Pulled the filter board for examination.  Solder joints look okay
(take a peek yourself: <http://merzhaus.org/ham/k1.80.15.jpg>) to me
(no bridges, good contact everywhere).  Beyond the basic resistance
checks in the build manual, I switched to band 2, then powered down
the rig.  I then verified 0, or infinite resistance between the
following points:

K1, pin 8-9, infinite
K1, pin 8-7, 0.3ohm
K1, pin 3-2, infinite
K1, pin 3-4, 0.3ohm
(relay seems to be latched in the right direction)

K2, pin 8-9, infinite
K2, pin 8-7, 0.3ohm
K2, pin 3-2, infinite
K2, pin 3-4, 0.3ohm
(relay seems to be latched in the right direction)

K3, pin 8-9, infinite
K3, pin 8-7, 0.3ohm
K3, pin 2-3, infinite
K3, pin 2-4, 0.3ohm
(relay seems to be latched in the right direction)

L7, L8, L3, L4, pins 1-3, 0.4ohm

L9, L10, L11, L12, 0.3ohm
(toroids stripped well enough to make good contact, counted turns
also, and L11, L12 both have 12 turns)

Having failed to find anything exciting in the visual and DMM checks,
I fired up the oscilloscope.  Mind you, I don't claim to be any kind
of expert at using a scope.. I can poke the probe at places I think
there should be a signal, and make a nice wide band show up on the
screen.  I can fiddle with a knob (time division) and make that band
blur, or slow to a crawl as it scans across the screen (I usually let
it blur).  I can fiddle with another knob (amplitude division) to make
things taller or shorter on the display.  Anyway, that's about the
extent of my scope knowledge (other than hooking a probe up to "CAL"
and adjusting things back into alignment).  So, with my limited
scope-using abilities, here's what I find:

With the K1 powered up:

Band 1 selected, probe to filter-board P1, pin 4: nice wide signal (6
divisions worth) seen on the scope
Band 2 selected, probe to filter-board P1, pin 4: signal on the scope
is very narrow (1 division total)

Pulling the bottom cover off the K1 to probe a few more points, I find
that when band 1 is selected, I see nice wide signals at all the
exciting points (ANT, PA, DRV, MIX, PRE, OSC).  When I select band 2,
everything pretty much stays the same, except for ANT and PA... both
of them now barely show up on the scope... if band1 was 8 divisions
high on the scope (4 up, 4 down from center) at .5V/div, band 2 is
about 1 division (1/2div up and 1/2 down) at 2mV/div (or completely
unseen at .5V/div).  So, if I'm understanding correctly, that
basically is just confirming that almost no signal is heading out of
this thing on 15M.  But why?!

Any thoughts?

-detrick
KI4STU
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[Detrick Merz]

Well, I think I have this one sorted out.  Here's how it boiled down
for me, in case anyone else gets anything similar:

1) Reflowed *every* solder joint on the filter board.  Added a bit of
solder to the ones that looked like they could handle a little more

2) Reinstalled the filterboard and experienced *no* change (still
9.9:1swr, no appreciable power out).

3) Tuned around to find some kind of signal.

4) Repeaked the filters (they did take a bit of adjusting, and signals
got stronger)

5) Asked the KAT1 to tune.. it found 1.6:1 this time.  Tested
transmitting, and while no one responded, the rig was showing 4 watts
out.

So, I guess the filters were far enough out of whack to be blocking
the signals I wanted.  Adjusting them again seemed to do the trick!
Thanks to everyone who replied with suggestions (and, the "shadow" one
person saw turned out to just be a bit of solder resin).  Now, if I
can just find something decent on 15M :)

-detrick
KI4STU

On 5/28/07, Detrick Merz <[hidden email]> wrote:
> Folks,
>
> I built my K1 around the end of last year (my favourite xmas
> present!).  Originally I had a 2 band module with 80/15 on it.  A few
> months later, I bought a second 2 bander, with 40/30.  The 40/30 works
> fine on both bands, but I can't get 15 to play nice on the 80/15
> module!
<snip>
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