Wayne,
The series resistors do not appear to be documented on the most recent
(June 2010) schematic package. At least I can't find any on the front
panel board, mainboard, or anywhere on the KIO3.
73,
... Joe, W4TV
On 8/28/2012 4:07 PM, Dave Hachadorian wrote:
> Wayne,
>
> Do you mean the 470 ohm resistors added to the KIO3 Board? If
> so, both radios had this mod done well before the speaker amps
> blew.
>
> Dave Hachadorian, K6LL
> Big Bear Lake, California
>
> -----Original Message-----
> From: Wayne Burdick
> Sent: Tuesday, August 28, 2012 11:18 AM
> To: Dave Hachadorian
> Cc: Elecraft Reflector
> Subject: Re: [Elecraft] K3 speaker audio gone!
>
> 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@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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