K-2 Audio problem

[Maxwell Moon]

Hello,
My K-2 audio sometimes fades completely away. It can happen whether I'm in RX or
TX mode. (Yes, the sidetone can fade to faint or no signal.)

Sometimes the audio comes back up almost to the original level, sometimes even
all the way back. But it fades again before too long. And it happens with an
external speaker or headphones, too.

This doesn't happen when I've just powered up. In fact, it's probably always
more than 15 or 20 minutes but I've never remembered to note the exact time.

If the audio stays weak, I can almost always recover it by turning the AF up
until the audio makes an odd sound, sort of like a bubble bursting. I may have
to rotate the knob to the 3 or 4 o'clock position, and sometimes I go all the
way & it still doesn't come back. But after it's back, it stays that way for at
least a few minutes.

The serial number of my K-2 is 9xx (I'm not being discrete or protecting my
privacy--I just can't remember & don't want to climb the stairs to check on the
rig itself ;-) It's a CW-only rig with the I/O, 160M, & NB mods. The filter
cases were grounded, filters aligned with Spectrogram, & several other mods
completed last year including installation of the speaker grill cloth (you don't
suppose *that's* the problem, maybe the fabric has too tight a weave for the
sound to get out??).

Well, that probably tips you off to my level of RF sophistication. So, if any of
you can suggest what I should check or look for, I'd be very grateful.

72,
Max, k0max


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[Don Brown-4]

Hi

As you describe your problem occurring with the side tone as well as the received signal I would suspect something in the AF amp circuit. Look for a bad connection, missing or wrong part around U9 on the control board. If you cannot find anything U9 may be bad. If you need to replace U9 cut all of the pins next to the body. Then using tweezers or needle nose pliers remove each pin while heating the pad. Clean out the holes with a solder sucker or tooth pick and then install the replacement IC.


Don Brown
KD5NDB

  ----- Original Message -----
  From: Maxwell Moon<mailto:[hidden email]>
  To: Elecraft List<mailto:[hidden email]>
  Sent: Tuesday, August 24, 2004 10:06 PM
  Subject: [Elecraft] K-2 Audio problem


  Hello,
  My K-2 audio sometimes fades completely away. It can happen whether I'm in RX or
  TX mode. (Yes, the sidetone can fade to faint or no signal.)

  Sometimes the audio comes back up almost to the original level, sometimes even
  all the way back. But it fades again before too long. And it happens with an
  external speaker or headphones, too.

  This doesn't happen when I've just powered up. In fact, it's probably always
  more than 15 or 20 minutes but I've never remembered to note the exact time.

  If the audio stays weak, I can almost always recover it by turning the AF up
  until the audio makes an odd sound, sort of like a bubble bursting. I may have
  to rotate the knob to the 3 or 4 o'clock position, and sometimes I go all the
  way & it still doesn't come back. But after it's back, it stays that way for at
  least a few minutes.

  The serial number of my K-2 is 9xx (I'm not being discrete or protecting my
  privacy--I just can't remember & don't want to climb the stairs to check on the
  rig itself ;-) It's a CW-only rig with the I/O, 160M, & NB mods. The filter
  cases were grounded, filters aligned with Spectrogram, & several other mods
  completed last year including installation of the speaker grill cloth (you don't
  suppose *that's* the problem, maybe the fabric has too tight a weave for the
  sound to get out??).

  Well, that probably tips you off to my level of RF sophistication. So, if any of
  you can suggest what I should check or look for, I'd be very grateful.

  72,
  Max, k0max


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[Tom Hammond-3]

Hi Max:

Don gave you some good suggestions there, but...

Were it me, given that the problem comes and goes and is not necessarily
present at turn-on. I think I'd first look for a flakey (or unsoldered)
joint in the AF chain. This sounds like a connection that fails after
things warm up just a bit... and might tend to move just a hair with
expansion from the heating.

When it fails, try (selectively) touching components in the audio chain
with an INSULATED tool... if touching one causes the sound to return,
chances are that (or at least something very close to it) is your culprit...

Sometimes, just the lease movement can cause a failed connection to 'renew'
for a while, only to fail again... usually just when you need it the most.

73,

Tom Hammond    N0SS

At 07:43 AM 8/25/04, Don Brown wrote:

>Hi
>
>As you describe your problem occurring with the side tone as well as the
>received signal I would suspect something in the AF amp circuit. Look for
>a bad connection, missing or wrong part around U9 on the control board. If
>you cannot find anything U9 may be bad. If you need to replace U9 cut all
>of the pins next to the body. Then using tweezers or needle nose pliers
>remove each pin while heating the pad. Clean out the holes with a solder
>sucker or tooth pick and then install the replacement IC.
>
>
>Don Brown
>KD5NDB
>
>   ----- Original Message -----
>   From: Maxwell Moon<mailto:[hidden email]>
>   To: Elecraft List<mailto:[hidden email]>
>   Sent: Tuesday, August 24, 2004 10:06 PM
>   Subject: [Elecraft] K-2 Audio problem
>
>
>   Hello,
>
>   My K-2 audio sometimes fades completely away. It can happen whether I'm
> in RX or
>   TX mode. (Yes, the sidetone can fade to faint or no signal.)
>
>   Sometimes the audio comes back up almost to the original level,
> sometimes even
>   all the way back. But it fades again before too long. And it happens
> with an
>   external speaker or headphones, too.
>
>   This doesn't happen when I've just powered up. In fact, it's probably
> always
>   more than 15 or 20 minutes but I've never remembered to note the exact
> time.
>
>   If the audio stays weak, I can almost always recover it by turning the
> AF up
>   until the audio makes an odd sound, sort of like a bubble bursting. I
> may have
>   to rotate the knob to the 3 or 4 o'clock position, and sometimes I go
> all the
>   way & it still doesn't come back. But after it's back, it stays that
> way for at
>   least a few minutes.
>
>   The serial number of my K-2 is 9xx (I'm not being discrete or protecting my
>   privacy--I just can't remember & don't want to climb the stairs to
> check on the
>   rig itself ;-) It's a CW-only rig with the I/O, 160M, & NB mods. The filter
>   cases were grounded, filters aligned with Spectrogram, & several other mods
>   completed last year including installation of the speaker grill cloth
> (you don't
>   suppose *that's* the problem, maybe the fabric has too tight a weave
> for the
>   sound to get out??).
>
>   Well, that probably tips you off to my level of RF sophistication. So,
> if any of
>   you can suggest what I should check or look for, I'd be very grateful.
>
>   72,
>   Max, k0max
>
>
>   _______________________________________________
>   Elecraft mailing list
>   Post to: [hidden email]<mailto:[hidden email]>
>   You must be a subscriber to post to the list.
>   Subscriber Info (Addr. Change, sub, unsub etc.):
> http://mailman.qth.net/mailman/listinfo/elecraft<http://mailman.qth.net/mailman/listinfo/elecraft>
>
>   Help:
> http://mailman.qth.net/subscribers.htm<http://mailman.qth.net/subscribershtm>
>   Elecraft web page: http://www.elecraft.com<http://www.elecraft.com/>
>_______________________________________________
>Elecraft mailing list
>Post to: [hidden email]
>You must be a subscriber to post to the list.
>Subscriber Info (Addr. Change, sub, unsub etc.):
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