K3 Configuration - No mono plugs in the stereo spkr jack!

[Eric Manning]

DO NOT, repeat NOT, plug a mono plug into the stereo speaker jack on the
back of your K3.

The manual says that the microprocessor firmware will switch the audio
to SPKRS 1, which it will.

However, if there are other events queued up for the cpu to process, it
may take some milliseconds, during which time

the shorted output may blow the audio amp, which is chip U1 of the DSP
board. {What is the audio output doing on the DSP board instead of the I/O board? - but that's
another story}

You then get to replace the DSP board - like I did  -  which is
good fun but  a fair amount of effort. And it costs the company $.

eric

VA7DZ



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[Dave Hachadorian]

Here's another way to blow U1 - turn off the agc and tune across
a very loud signal.

As I have said before, the audio amp should not be this fragile.
It needs better protection.

Dave Hachadorian, K6LL
Yuma, AZ

--------------------------------------------------
From: "eric manning" <[hidden email]>
Sent: Thursday, February 25, 2010 8:25 AM
To: <[hidden email]>
Subject: [Elecraft] K3 Configuration - No mono plugs in the
stereo spkr jack!

>
> DO NOT, repeat NOT, plug a mono plug into the stereo speaker
> jack on the
> back of your K3.
>
> The manual says that the microprocessor firmware will switch
> the audio
> to SPKRS 1, which it will.
>
> However, if there are other events queued up for the cpu to
> process, it
> may take some milliseconds, during which time
>
> the shorted output may blow the audio amp, which is chip U1 of
> the DSP
> board. {What is the audio output doing on the DSP board instead
> of the I/O board? - but that's
> another story}
>
> You then get to replace the DSP board - like I did  -  which is
> good fun but  a fair amount of effort. And it costs the company
> $.
>
> eric
>
> VA7DZ
>
>
>
> --
> This message has been scanned for viruses and
> dangerous content by MailScanner, and is
> believed to be clean.
>
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:[hidden email]
>
> This list hosted by: http://www.qsl.net
> Please help support this email list:
> http://www.qsl.net/donate.html 

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[ab2tc]

Hi,

Although I never turn off my AGC (I use headphones and I don't want to lose my hearing), I agree that the audio amp should not be this fragile. It's surprising since there are a lot of audio amplifier chips out there that are virtually indestructible using load line and over temperature protection circuits. Seems like Elecraft didn't pick the right one.

On a different subject, it seems that TX4T has now gone QRT after a very successful expedition with their K3s. Hopefully they didn't need the spare one they wisely brought with them. I finally managed to work them on 15m today on their last day of operation. It's very encouraging to see the increasing use of K3s in this kind of operations.

AB2TC - Knut

Dave Hachadorian wrote

Here's another way to blow U1 - turn off the agc and tune across
a very loud signal.

As I have said before, the audio amp should not be this fragile.
It needs better protection.

Dave Hachadorian, K6LL
Yuma, AZ
<snip>