Seeking Help Solving KAF2 Problem

[Dennis Payton]

A couple weeks ago, I got out my K2 and operated the ARRL International DX
Contest. During the contest, my audio output was so low I had to constantly
use the preamp just to hear on my headphones, so afterwards I opened the rig
up and tracked the problem down to the audio filter. Shorting pins 1 & 2 of
J1 & J2 gave me full audio with the board removed, and flipping the
board-mounted switch to "out" gave me full audio with the board installed.



That told me the problem 'had' to be in the filter board, but after checking
the DC voltages from the chart and thoroughly examining each component's
location and solder joints, I found nothing. I decided to use a RS
speaker-amp to follow the audio signal through the filter to see where it
was getting attenuated, but was very surprised to not see it getting
attenuated anywhere. The filter appears to work properly from beginning to
end. The audio at pins 1 & 2 of J1 & J2 all sound fine to me, whether the
filter is switched in or out, but the K2's audio is 'greatly' attenuated
when the filter is switched in. Although I'd made sure the filters were
aligned with each other when I first started troubleshooting, I thought that
was all that was left, so I started checking them again. Then, at one point,
I hit the "spot" button and discovered I suddenly had no sidetone. I spent
quite a bit of time trying to figure out what happened, but couldn't get any
power from pin 25 of the MCU whether I keyed the rig, hit "spot", or turned
the rig off & on. Then as a curiosity after giving up, I removed the audio
filter board. That gave me sidetone again! Next, I reinstalled the board and
I still had sidetone, so something must have "locked up"? Now, I've got the
filter removed again though, and have decided that I'm at the end of my
ability.



Something else I think I should mention is that I measure 5.15 volts on pins
1 & 2 of  J1 on the control board. I hope that's expected. Also, I don't
know if I've had this problem since the beginning or if it just popped up. I
haven't operated the K2 since installing the KAF2 quite some time ago, and I
just don't remember how I left it.



Any advice would sure be appreciated.



Thanks!



Denny Payton    N9JXY



(By the way, I worked Auckland, New Zealand on 40-meters during the contest
operating one watt. That calculated to be 8312 miles-per-watt, which is by
far a new record for me. My antenna is just an R7 vertical mounted on a shed
in my back yard.)


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[n8ewy]

This is a post I used and then archived and may help you.

Your sidetone source likely was switched for some reason or other - maybe by
an 'extra' finger press while in the menu

Go back into the menu and dial up ST L, press EDIT to move the cursor over
to the right side and then tap DISPLAY to toggle the sidetone source.  When
you hear the sidetone, stop and exit from the menu.

In some rare instances, it may take a few 'toggles' to get things to switch
properly, so try it several times.  If you have a post SN 3000 K2 (or have
put the sidetone source change on an older K2 because you added the KPA100
or KIO2) your sidetone source should be 'U8 - 4' - you will see the source
displayed briefly each time it is toggled.

73,
Don W3FPR

Dohn   N8EWY

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Dennis Payton
Sent: Thursday, March 01, 2007 10:19 PM
To: [hidden email]
Subject: [Elecraft] Seeking Help Solving KAF2 Problem

A couple weeks ago, I got out my K2 and operated the ARRL International DX
Contest. During the contest, my audio output was so low I had to constantly
use the preamp just to hear on my headphones, so afterwards I opened the rig

up and tracked the problem down to the audio filter. Shorting pins 1 & 2 of
J1 & J2 gave me full audio with the board removed, and flipping the
board-mounted switch to "out" gave me full audio with the board installed.



That told me the problem 'had' to be in the filter board, but after checking

the DC voltages from the chart and thoroughly examining each component's
location and solder joints, I found nothing. I decided to use a RS
speaker-amp to follow the audio signal through the filter to see where it
was getting attenuated, but was very surprised to not see it getting
attenuated anywhere. The filter appears to work properly from beginning to
end. The audio at pins 1 & 2 of J1 & J2 all sound fine to me, whether the
filter is switched in or out, but the K2's audio is 'greatly' attenuated
when the filter is switched in. Although I'd made sure the filters were
aligned with each other when I first started troubleshooting, I thought that

was all that was left, so I started checking them again. Then, at one point,

I hit the "spot" button and discovered I suddenly had no sidetone. I spent
quite a bit of time trying to figure out what happened, but couldn't get any

power from pin 25 of the MCU whether I keyed the rig, hit "spot", or turned
the rig off & on. Then as a curiosity after giving up, I removed the audio
filter board. That gave me sidetone again! Next, I reinstalled the board and

I still had sidetone, so something must have "locked up"? Now, I've got the
filter removed again though, and have decided that I'm at the end of my
ability.



Something else I think I should mention is that I measure 5.15 volts on pins

1 & 2 of  J1 on the control board. I hope that's expected. Also, I don't
know if I've had this problem since the beginning or if it just popped up. I

haven't operated the K2 since installing the KAF2 quite some time ago, and I

just don't remember how I left it.



Any advice would sure be appreciated.



Thanks!



Denny Payton    N9JXY



(By the way, I worked Auckland, New Zealand on 40-meters during the contest
operating one watt. That calculated to be 8312 miles-per-watt, which is by
far a new record for me. My antenna is just an R7 vertical mounted on a shed

in my back yard.)


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[Dennis Payton]

I haven't received any comments about my audio filter problem yet, so
tonight I tried a few more things to no avail, and took some VAC
measurements with a fairly accurate voltmeter. The signal came from the
10Mhz. oscillator shown in the manual.
With the filter switched out, J1 & J2 pin 1 measured .030 and pin 2 measured
.018 (shouldn't they be equal?). At the LM380 (had to solder a couple wires
to the pins & stick them out from between the boards) pin 2 measured .004
and pin 3 measured .008. At the speaker (volume control centered) it
measured .292 and the volume was very good.
With the filter switched in, J1-1 measured .036 and J2-1 measured .056; J1-2
measured .022 and J2-2 measured .053. At the LM380 the voltage at pins 2 & 3
then measured .058 VAC on both, and the voltage at the speaker was way down
to .008.
I also took a couple DC measurements. With the filter out, the four pins had
5.1V. on them, and with it switched in, J1's pins were still at 5.1V. and
J2's pins measured 6.03V. Do these additional measurements I took give
anybody any ideas?
Thanks again,
Denny Payton     N9JXY
..................................................

>A couple weeks ago, I got out my K2 and operated the ARRL International DX
> Contest. During the contest, my audio output was so low I had to
> constantly
> use the preamp just to hear on my headphones, so afterwards I opened the
> rig
> up and tracked the problem down to the audio filter. Shorting pins 1 & 2
> of
> J1 & J2 gave me full audio with the board removed, and flipping the
> board-mounted switch to "out" gave me full audio with the board installed.
>
> That told me the problem 'had' to be in the filter board, but after
> checking
> the DC voltages from the chart and thoroughly examining each component's
> location and solder joints, I found nothing. I decided to use a RS
> speaker-amp to follow the audio signal through the filter to see where it
> was getting attenuated, but was very surprised to not see it getting
> attenuated anywhere. The filter appears to work properly from beginning to
> end. The audio at pins 1 & 2 of J1 & J2 all sound fine to me, whether the
> filter is switched in or out, but the K2's audio is 'greatly' attenuated
> when the filter is switched in. Although I'd made sure the filters were
> aligned with each other when I first started troubleshooting, I thought
> that
> was all that was left, so I started checking them again. Then, at one
> point,
> I hit the "spot" button and discovered I suddenly had no sidetone. I spent
> quite a bit of time trying to figure out what happened, but couldn't get
> any
> power from pin 25 of the MCU whether I keyed the rig, hit "spot", or
> turned
> the rig off & on. Then as a curiosity after giving up, I removed the audio
> filter board. That gave me sidetone again! Next, I reinstalled the board
> and
> I still had sidetone, so something must have "locked up"? Now, I've got
> the
> filter removed again though, and have decided that I'm at the end of my
> ability.
>
> Something else I think I should mention is that I measure 5.15 volts on
> pins
> 1 & 2 of  J1 on the control board. I hope that's expected. Also, I don't
> know if I've had this problem since the beginning or if it just popped up.
> I
> haven't operated the K2 since installing the KAF2 quite some time ago, and
> I
> just don't remember how I left it.

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[Don Wilhelm-3]

Dennis,

Are you certain your KAF2 is tuned to your sidetone pitch?  If it is not it
will severely attenuate your signal.

There is no need for the AC voltages at the headers pin 1 to match the
voltages at pin 2.  The filter and the input to the audio amplifier are
differential inputs and the measurement must be between the two pins to
indicate how it is working.  It is more than just a matter of subtracting
the two AC voltages to obtain the drive levels because the phase of the
signals must be considered too. If you have an ungrounded AC meter, measure
the voltage between the pins.  If you are observing with a 'scope, remember
that the scope is grounded and you must use two probes - invert one channel
and add the two to see the differential voltage.

I would suggest that you check the components on the KAF2 board for correct
values and good soldering.  Especially check R9, R10, and C16 because these
operate a phase shifter to restore the balanced output (the filter sections
themselves are single ended).

The temporarily lost sidetone is not related - the sidetone is injected into
the LM380 audio amplifier  by a separate path from the receiver audio.

73,
Don W3FPR

> -----Original Message-----
>
> I haven't received any comments about my audio filter problem yet, so
> tonight I tried a few more things to no avail, and took some VAC
> measurements with a fairly accurate voltmeter. The signal came from the
> 10Mhz. oscillator shown in the manual.
> With the filter switched out, J1 & J2 pin 1 measured .030 and pin
> 2 measured
> .018 (shouldn't they be equal?). At the LM380 (had to solder a
> couple wires
> to the pins & stick them out from between the boards) pin 2 measured .004
> and pin 3 measured .008. At the speaker (volume control centered) it
> measured .292 and the volume was very good.
> With the filter switched in, J1-1 measured .036 and J2-1 measured
> .056; J1-2
> measured .022 and J2-2 measured .053. At the LM380 the voltage at
> pins 2 & 3
> then measured .058 VAC on both, and the voltage at the speaker
> was way down
> to .008.
> I also took a couple DC measurements. With the filter out, the
> four pins had
> 5.1V. on them, and with it switched in, J1's pins were still at 5.1V. and
> J2's pins measured 6.03V. Do these additional measurements I took give
> anybody any ideas?
> Thanks again,
> Denny Payton     N9JXY
> ..................................................
> >A couple weeks ago, I got out my K2 and operated the ARRL
> International DX
> > Contest. During the contest, my audio output was so low I had to
> > constantly
> > use the preamp just to hear on my headphones, so afterwards I
> opened the
> > rig
> > up and tracked the problem down to the audio filter. Shorting
> pins 1 & 2
> > of
> > J1 & J2 gave me full audio with the board removed, and flipping the
> > board-mounted switch to "out" gave me full audio with the board
> installed.
> >
> > That told me the problem 'had' to be in the filter board, but after
> > checking
> > the DC voltages from the chart and thoroughly examining each component's
> > location and solder joints, I found nothing. I decided to use a RS
> > speaker-amp to follow the audio signal through the filter to
> see where it
> > was getting attenuated, but was very surprised to not see it getting
> > attenuated anywhere. The filter appears to work properly from
> beginning to
> > end. The audio at pins 1 & 2 of J1 & J2 all sound fine to me,
> whether the
> > filter is switched in or out, but the K2's audio is 'greatly' attenuated
> > when the filter is switched in. Although I'd made sure the filters were
> > aligned with each other when I first started troubleshooting, I thought
> > that
> > was all that was left, so I started checking them again. Then, at one
> > point,
> > I hit the "spot" button and discovered I suddenly had no
> sidetone. I spent
> > quite a bit of time trying to figure out what happened, but
> couldn't get
> > any
> > power from pin 25 of the MCU whether I keyed the rig, hit "spot", or
> > turned
> > the rig off & on. Then as a curiosity after giving up, I
> removed the audio
> > filter board. That gave me sidetone again! Next, I reinstalled
> the board
> > and
> > I still had sidetone, so something must have "locked up"? Now, I've got
> > the
> > filter removed again though, and have decided that I'm at the end of my
> > ability.
> >
> > Something else I think I should mention is that I measure 5.15 volts on
> > pins
> > 1 & 2 of  J1 on the control board. I hope that's expected. Also, I don't
> > know if I've had this problem since the beginning or if it just
> popped up.
> > I
> > haven't operated the K2 since installing the KAF2 quite some
> time ago, and
> > I
> > just don't remember how I left it.
>
>
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[Dennis Payton]

> Are you certain your KAF2 is tuned to your sidetone pitch?  If it is not
> it
> will severely attenuate your signal.

The trimmers are peaked to the sidetone, but the audio is also just as
attenuated in the "off" selection.

> I would suggest that you check the components on the KAF2 board for
> correct
> values and good soldering.  Especially check R9, R10, and C16 because
> these
> operate a phase shifter to restore the balanced output (the filter
> sections
> themselves are single ended).

R9, R10, & C16 all tested good, but I ended up removing C16 to test it
accurately. Then I was afraid the stress may have damaged it so replaced it
with another 470pf NPO.

VAC measurements between the pins with the filter in were .077 at J1, .005
at J2, and .000 at the LM380. With the filter switched out it measured .061
at J1/J2, and .008 at the LM380. I guess that says the problem is in the
filter?

Thanks for the advice, Don!

Denny    N9JXY.


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