[Elecraft] DSP Mute Problem

[Charles Bland]

On my first road trip after assembling and installing my DSP board, I started 
having problems with the audio muting. It would start intermittently, then 
eventually would mute completely.

Power cycles would fix the problem, but at times it would take one or two, and 
occasionally some time.

After much troubleshooting, I have discovered that the voltage on the collector 
of Q7 stays stable for a few minutes, then it wanders between two and three 
volts. I've been watching it on an oscilloscope.

I'm presuming since the audio does initially pass through the unit that Q5 and 
Q6 are OK. That is reinforced by the fact that audio does mute when the voltage 
dips and wanders.

During the wandering, the MUTE line is stable in the "unmute" state.

My vote is for Q7, the 2N3904, being the culprit.

Lyle? Gary? Does that sound about right to you too? I'm gonna sleep on this 
before I try to change it (gotta see if I have one in the junk box anyway.)

Chuck
#1924