[Elecraft] deaf receiver...

[Nate Lewis]

I've got a mostly-deaf K2 that seems to think that all signal or noise is S3
at best, on all bands, and puts out very quiet audio.  I have the luxury of
a second K2 that is working perfectly.  both are rev B.

Last night, using logic that escapes me now, I determined that my trouble
had to be around the IF amp, so I was probing around with a scope.  After
the crystal filter, and especially after the amp, I should expect to see a
frequency in the neighborhood of 5mhz with some ~2khz noise modulated onto
it, should I not?  but when I put it on the scope, I get the same thing on
either rig: a signal so weak and high-frequency that I don't really believe
it was real.  Shouldn't I be able to see something recognizable here on a
scope?

Other symptoms: last time I was poking around with it, I found it suddenly
heard a great deal better when I clipped the ground leads of certain test
equipment onto the K2 ground (I don't know what real grounding, if any, I'm
getting off my power supplies - I wouldn't be surprised if all my grounds
are just floating).  Turning off AGC has some very small effect (and the
control board from the bad K2 sounds great in the good one).  I tuned it up
for transmit before realizing how bad the receive level was, and transmit
seems just fine.

The session before, the problem seemed to be only on higher bands, getting
progressively worse on each band above 40.  I remember looking at signal
levels on different bands and finding greater attenuation after the BPF
relative to, say, W6, the higher the frequency I was looking for.  since the
progression was smooth across many bands, I was speculating that the receive
mixer or something ahead of it might be loading the signal down at higher
frequencies, and poking around injecting signal or noise after the bandpass
filters - there's a distinct possibility I hit the receive mixer with a much
larger signal than it expects, possibly tens of volts.  Might I have cooked
it?

tonight, I guess I'll stop trying to reason about things I don't quite
understand and just wade through the troubleshooting in the manual, if I
convince myself that I trust my signal generator's attenuator, but any other
advice would be welcome.