[Elecraft] K3 speaker audio gone!

Tue Aug 28 15:17:37 EDT 2012

See: http://www.elecraft.com/K3/mods/AF_Output_Mod_Rev_C.pdf

"This modification is needed for all K3s shipped to date containing
either a Revision XB or Revision A KIO3
board. You must inspect the KIO3 board to see whether the modification
has been made. Modified boards will
include the leaded resistors shown in Figure 4. You can see the
resistor in the lower part of the figure by removing
the top cover as shown in Figure 1 and inspecting the side of the KIO3
board facing away from the rear panel.  "

Also http://www.elecraft.com/K3/k3_app_notes.htm states "Included on
all new K3s About 12/23/08 and later."

73,

    ~iain / N6ML

On Tue, Aug 28, 2012 at 11:31 AM, hawley, charles j jr
<c-hawley at illinois.edu> wrote:
> Was there a serial # that included the current limiting?
>
> Sent from my iPhone
>
> On Aug 28, 2012, at 1:18 PM, "Wayne Burdick" <n6kr at elecraft.com> wrote:
>
>> Dave,
>>
>> Do you have the AF amp current-limiting mod in place? The parts for
>> this mod are installed on the RF board. They've been in production for
>> quite some time, and we can send them to you on request.
>>
>> With the limiter installed, we've seen near-zero problems with the AF
>> amp IC.
>>
>> 73,
>> Wayne
>> N6KR
>>
>>
>>
>> On Aug 28, 2012, at 10:25 AM, Dave Hachadorian wrote:
>>
>>> I have blown the speaker amp twice, in two different radios, by
>>> using a speaker with AGC OFF.  POOF! Gone before you can react by
>>> turning down the audio.
>>>
>>> The factory guys report that they have been unable to duplicate
>>> the problem.  Unless you are an EXPERT solderer, replacing the
>>> speaker amp chip is best done by the factory.  The job will run
>>> about $125 with shipping, maybe a little less if you ship only
>>> the DSP Board.  I don't use the speaker amp any more.  I still
>>> think there is a transient susceptibility problem in that
>>> circuitry that they have been unable to find.
>>>
>>>
>>> Dave Hachadorian, K6LL
>>> Big Bear Lake, California
>>>
>>>
>>>
>>>
>>>
>>>
>>> -----Original Message-----
>>> From: Mike Goldstein
>>> Sent: Tuesday, August 28, 2012 9:07 AM
>>> To: elecraft at mailman.qth.net
>>> Subject: [Elecraft] K3 speaker audio gone!
>>>
>>>        I've lost audio from both the internal speaker in the
>>> K3,
>>> and from the SPKRS output jack on the rear panel.
>>>
>>>        At the end of the the first week of using a new NESCAF
>>> audio
>>> filter (which drives my speaker) with the K3,  I changed bands,
>>> listened briefly on CW, with the NESCAF filter in the circuit.  I
>>> then changed to SSB, and because the NESCAF filter was adjusted
>>> for a
>>> very narrow audio bandwidth, I decided to switch it out of the
>>> circuit, while the K3 was delivering audio, at a comfortable
>>> listening level..
>>>
>>>        The audio filter was driven from the SPKRS jack on the
>>> back
>>> of the K3, using a stereo plug, with one channel floating.  The
>>> SPKRS
>>> jack was CONFIGured as SPKRS = 1.
>>>
>>> A front panel toggle switch on the filter panel turns off the
>>> power
>>> to the NESCAF filter, and re-routes the speaker audio connection
>>> from
>>> the filter output, to the K3 output directly. I had done this
>>> often,
>>> for the first week of operations.
>>>
>>> This time, however, I briefly saw a "HI CURR" indication on the
>>> front
>>> panel of the K3, and then my speaker audio vanished.
>>>
>>> Unplugging all connections from the rear panel SPKRS jack, and
>>> the
>>> front panel PHONES jack, no longer allows the K3's internal
>>> speaker
>>> to produce audio.  Nothing I tried would result in any audio from
>>> the
>>> external speaker, after connecting that speaker to either of the
>>> phono jacks that were tied to the rear SPKRS jack, through the
>>> stereo plug.
>>>
>>> The INPUT jack on the SCAF filter (to which the K3's SPKRS jack
>>> was
>>> connected) passes through an isolating capacitor, then a 27K
>>> resistor, before being connected to the chip in the audio filter.
>>>
>>> Resetting SPRKS = 2, in the  CONFIG menu, had no effect on
>>> producing
>>> audio in the external, or internal speaker.
>>>
>>> I still have audio  at the PHONES jack on the front panel, so I
>>> can
>>> still use the K3.  It subsequently accounted for 380 QSOs in the
>>> NAQP
>>> CW contest, providing it usual flawless performance.
>>>
>>> I still have audio at the PHONES jack on the rear panel, as well.
>>>
>>> My theory (and Gary at Elecraft Service agrees it might be the
>>> cause)
>>> is that the audio chip in the K3 didn't like the abrupt change of
>>> load impedance, from 27K (approx.) to infinity, to 8 ohms, while
>>> it
>>> was delivering audio..
>>>
>>> I've since soldered a 15K resistor across the input jack of the
>>> audio
>>> filter, and will do likewise for any other audio filters I
>>> encounter, and use.
>>>
>>> Puzzling, huh?  73 de  VE3GFN
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>>
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