[Elecraft] K3: KPA100 Squeal

[Bill W4ZV]

FYI another update to this.  I had the same audio squeal on #4717 and asked
Gary AB7MY about it around the same time AB3LS's unit was in for repair. 
According to Dale K6ZP in Elecraft Service, the fix was:

"The KPA3 that is in for this problem has been fixed.  The MMT3904 Q7 used
as the 18 Mhz oscillator was turning off and on at ~ 15 khz rate, modulating
the 18 Mhz.  Replacing Q7 cleared the problem. "

Since I had the same problem whenever my unit warmed up, Gary sent me a
replacement for Q7.  It requires removing the KPA3 module and Q7 is on the
underside of the board.  Q7 a small SMD transistor but is easy to access. 
You can replace it yourself if you're familiar with SMD work.  I cut the
existing device with nippers which made it easy to remove the 3 legs without
damaging the PCB pads.

After a good warmup calling 3C0E on 10m this morning my PA temp reached ~31C
and I no longer have any squeal.  BTW mine was always there after it got
really warmed up...not just when I transmitted.  I never noticed it before
AB3LS' comment because I seldom never have my high isolation headphones off,
but it would have definitely bothered someone with good hearing if they were
using the speaker.

73,  Bill  W4ZV




AB3LS wrote
> 
> I had some questions about this issue mailed to me.
> 
> Here's my update.
> 
> Elecraft sent me a replacement KPA100 and KPA I/O board, of which I
> replaced myself.
> 
> The new amplifier and I/O board fixed the problem. No more 12KHz
> resonation
> coming from the internals of the radio in test, low, and high power modes.
> The closest thing I can compare the sound to is the electrical resonation
> of a cathode ray tube in a TV, however, it's not as clean.
> 
> Possibly a cold solder joint or bad connection between the amplifier and
> I/O board? I don't know.
> 
> 73
> DE AB3LS
> 
> On Fri, Jul 29, 2011 at 4:29 PM, Bill W4ZV <btippett at .mit> wrote:
> 
>>
>> AB3LS wrote:
>> >
>> > No go.
>> >
>> > Hooked the radio up to a gel cel battery and we're still getting the
>> 12Khz
>> > junk coming from something and the clicking between TX and RX.
>> >
>> > I made a longer recording of the 'junk' and posted it. Cycled between
>> TX
>> > and
>> > RX a few times using the manual TX button on the front. Then finished
>> off
>> > with a few dits and dahs. All while in TX Test mode.
>> >
>> >
>> http://alien.liltechdude.com/files/index.php?dir=Recordings/&file=kpa3squealrev2.mp3
>> >
>> > Anyone from Elecraft have anything on this?
>> >
>>
>> FYI I noticed the same on my #4717 kit (delivered last September).  I
>> normally use headphones so I never noticed it before.  I believe ~12 kHz
>> was
>> getting into the DSP chain before the LPF mod to the DSP board was done
>> so
>> perhaps that's a clue.  BTW I have no switching PS anywhere and this is
>> definitely coming from the K3 itself.
>>
>> This would be VERY annoying to someone with good hearing in a quiet
>> shack.
>> I can minimize it by slight head movement (standing waves) but that's not
>> a
>> good solution.
>>
>> 73,  Bill
>>
>>
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