[Elecraft] help: k2 rf noise prob

[Robert G. Strickland]

#5957 w/ DSP, NB, SSB seems to have developed an RF noise problem.

With the radio setup this way:
 > antenna connected to dummy load, DSP off, NB off, AGC off, CW mode, 
AUD fully advanced

I get the following symptoms:
 > as RF gain is advanced a "frying noise" comes up, reaching about S5 
at max RF.
 > switching preamp/attenuator in and out doesn't change the problem 
"noise." I can hear real RF noise from the dummy load and preamp 
increase/decrease on top of the problem "noise."
 > changing the XTAL filter setting does change the "noise."
 > as the RF control is reduced from max to min, at about 2/3 max a soft 
"pop" is heard, the the S-meter reading goes all the way to max [as if 
the RF gain were fulling off] and then trails back towards S-0 as it was 
before the "pop." Afterwards, the S-meter reading continues to max as 
normal. It's as if the AGC were on, but it isn't.
 > switching AGC in/out doesn't alter the "noise."
 > switching DSP in alters the "noise" as the DSP circuit tries to 
handle it. As compared to the no-DSP condition, the "noise" with DSP 
comes up as brief static "spikes" that eventually blend into sound of 
the "noise" w/o DSP.
 > switching NB in/out doesn't alter the "noise."

In view of the above, I'm thinking that this noise is coming from Rcv 
Mixer [TUF-1] - Post-Mixer Amp [Q22] circuit area. Nothing before that 
seems to effect it, and the XTAL filter definitely reduces it. Any quick 
insights or trouble shooting steps that can help me reduce/eliminate 
this "noise" would be appreciated.

Thanks much.

...robert

Robert G. Strickland, PhD, ABPH - KE2WY
rcrgs at verizon.net
Syracuse, New York, USA