[TenTec] Help with deaf Argonaut 509...

[Roscoe Primrose]

My Argonaut 509 seems to have a serious receiver sensitivity problem.  
The other night when 80M was fairly noisy, I was getting noise at S6-S8 
on an FT817, hooked the same antenna to the 509, an even with the RF 
gain all the way up, the S-meter baorly moved, if at all.  RF noise is 
generally not enough to move the S-meter, and I've made several easily 
understandable QSOs with no motion of the S-meter.  The S-meter is 
working, with very strong signals it does occasionally get up to S-9.  I 
originally thought the problem was the first stage dual-gate MOSFET, but 
I'm pretty sure that's not the problem at this point.  When 
troubleshooting the first stage MOSFET, when I hooked a DMM lead to gate 
1 I get a stronger signal (not just noise, but signal as well) from the 
test lead than I do from the antenna connected to the unit.  On the RF 
front-end board, the antenna signal goes through an input cap, a 
transformer/cap combination that's a 9MHz trap (VFO), through a tuned 
transformer which is part of the pre-selector, through a coupling cap, 
and to gate1 on the MOSFET.  Connecting the DMM lead directly to gate1 
causes an increase in signal & noise, connecting it anywhere before the 
coupling cap results in no change in signal level.  I changed the 
coupling cap, but there was no change in performance.

Anyone familiar enough with the front-end on these rigs to have an idea 
as to what I can check next?

Thanks,  AJ4LL

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"The tree of liberty must be refreshed from time to time with the blood of patriots and tyrants. It is it's natural manure."
Thomas Jefferson, 1787.