[Elecraft] K3 Speaker Amp - sub side inop

[Don Wilhelm]

  Matt,

Yes it sounds like you have blown the right channel of the speaker audio 
amp.  The headphone amp is a different chip.

I don't know how to confirm that is what failed other than to devise a 
connection means for a 'scope at the input and output of each channel.

73,
Don W3FPR

On 8/27/2010 2:48 PM, Matt Zilmer wrote:
> Hi Don,
>
> I was wiring up a switch box for dual-sourcing hifi speakers, and
> looks like I had a short on the Sub (right) side circuit.  This may
> have damaged the speaker amp, U1 on the DSP board (sh 3 of 9 from
> 6/2010 schematics).
>
> Symptoms:
>
> If only the main RX is operating, output is roughly equal from both
> speakers.  BTW, the Sub AF is set to Balance.
>
> If the sub RX is also enabled in diversity with balance set full CW, I
> hear nothing.  If the control is set full CCW, I hear the main RX.
>
> If I use the headphone jack with sub RX enabled, I get the two signals
> as expected.
>
> --
>
> This seems to point to U1, the speaker amp on the DSP since the
> headphone output is OK for both channels.
>
> Is there some way to confirm U1 is bad?  I will be running a sig gen
> into the main and aux antenna inputs to drive the two channels
> separately and try to isolate the problem.
>
> Any ideas are welcome.  Meanwhile, is the LM4950TS stereo amp
> available as a component from Elecraft, and is it user-repairable?
>
> Many Thanks!
> matt W6NIA
> K3 #24, K2 #2810
>