[Elecraft] K3 Speaker Amp - sub side inop

[Matt Zilmer]

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