[Elecraft] K2 4907 - Still no audio

[Zac Brown]

Fellow builders,

I've been working on building my K2 as time permits since may of 2005.
I was hoping to have it completed by now, but got stuck on a problem and
haven't had the time to really delve into it until recently.

Back in 2005, I posted a question to the group - the topic was "No Audio 
Except during Menu".  I'm still having this problem.

I've been exchanging emails with Gary, and feel like I'm getting close 
to finding the problem.

Here's a summary of things that I've checked so far:

R12 looks fine, squelch is turned off, the 18C452 MCU looks fine 
(measuring all pins results in expected values, have already pulled the 
MCU and verified that all pins are straight, etc ... ), visual 
inspection of solder points revealed no solder bridges or cold solder 
joints, all resistance checks are passing.  Nothing aside from the base 
  K2 kit is installed.

D9, however, is exhibiting some strange behavior.

When I'm in normal receive mode, D9's cathode is measuring about 1.9 
VDC.  Gary tells me that it should be close to 0 VDC in receive mode, 
and that if it goes much above 1 to 2 VDC (in receive) that the MCU will 
turn off the 8R line, resulting in what appears to be a dead receiver.

When I go into the menu, as soon as I scroll past the ATU entry
(I have no ATU installed btw, just the base K2 kit), D9's cathode drops
to about 0 VDC, and I hear audio at that point.  It stays like that as 
long as I remain in the menu.  As soon as I exit the menu, D9's cathode 
goes back to about 1.9 VDC and I hear no audio.

If I put a piece of wire across D9's connection points (bypassing D9), 
then I hear audio all the time.

I feel like I'm getting close to finding the problem.  Any ideas what 
could be causing this?  It's probably something that I did wrong while 
building the radio, but I'm not sure where to look at this point.

Thanks,

Zac Brown
KD5IEF
K2# 4907