Iain, The mod you referenced below is a very old one (470 ohm resistors on the KIO3). It has been in production for a long time.
The mod I was talking about is newer (2010, I believe). It involves a pair of very small-valued resistors in series with the AF output coupling capacitors. This, too, is in production. However, I just looked on the K3 mods page, and it appears that we never did turn this into a mod kit. We'll get this corrected right away. Wayne N6KR On Aug 28, 2012, at 12:17 PM, iain macdonnell - N6ML wrote: > 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-haw...@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" <n...@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@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 >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:Elecraft@mailman.qth.net >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: >>>> http://www.qsl.net/donate.html >>>> >>>> ______________________________________________________________ >>>> Elecraft mailing list >>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>>> Help: http://mailman.qth.net/mmfaq.htm >>>> Post: mailto:Elecraft@mailman.qth.net >>>> >>>> This list hosted by: http://www.qsl.net >>>> Please help support this email list: http://www.qsl.net/donate.html >>> >>> ______________________________________________________________ >>> Elecraft mailing list >>> Home: http://mailman.qth.net/mailman/listinfo/elecraft >>> Help: http://mailman.qth.net/mmfaq.htm >>> Post: mailto:Elecraft@mailman.qth.net >>> >>> This list hosted by: http://www.qsl.net >>> Please help support this email list: http://www.qsl.net/donate.html >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> Help: http://mailman.qth.net/mmfaq.htm >> Post: mailto:Elecraft@mailman.qth.net >> >> This list hosted by: http://www.qsl.net >> Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
