[Elecraft] K3 - No speaker output

[Stewart]

Mine failed with a stereo (not a mono) plug which had been inserted prior to the 
K3 being powered on.

The external speaker of 8 ohms was wired onto the left channel (plug tip),
therefore the right channel did not have a load at the time. Don't know if this 
causes a problem.

The fault occurred when the AF gain on my K3 was advanced to approx 12 o'clock,
at which point the audio out the speaker failed.

So, the fault was NOT caused by shorting either of the outputs, or plugging in 
the speaker with the K3 powered on.

My K3 is an early Ser # 307

73
Stewart G3RXQ

On Tue, 14 Jan 2014 19:10:29 -0700, Dave Hachadorian wrote:
> Putting a mono plug into the stereo jack is not the ONLY failure
> mechanism for the speaker amplifier chip.  It was not the cause
> of failure of my two K3's.
>
> I'm not sure anyone fully understands the failure
> mechanisms in the speaker amplifier.
>
> The new $2.36 mod adds 1 ohm resistors in series with the audio
> output channels.  Hopefully that will do some good.
>
> Dave Hachadorian, K6LL
> Yuma, AZ
>
>
> -----Original Message-----
> From: Don Wilhelm
> Sent: Tuesday, January 14, 2014 5:10 PM
> To: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 - No speaker output
>
> Dick,
>
> If you have an early K3 *and* you plugged a mono connector into
> the rear
> speaker jack, one channel was shorted by the mono connector. That
> will
> cause failure of the audio amp for the speaker.
> Later K3s (I don't know the serial number) have protection for
> that
> shorting condition.  The best protection is not to put a mono
> plug into
> the speaker jack.  If you want mono, cut off the mono plug and
> connect
> only the tip and shell to your speaker - the ring does not
> connect to
> anything.
>
> 73,
> Don W3FPR
>
> On 1/14/2014 6:55 PM, Richard Solomon wrote:
>> Can someone explain to me exactly why the chip failed, and what
>> the Audio
>> Protection Assembly is for ?
>>
>> Tnx, Dick, W1KSZ
>>
>
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