[Swan] Sensitivity and meter on 500

[Jeff]

Hi all -

Seeking some advice on a 500.  This seems temperature related, and I'm 
having a hard time tracking it down.  I picked up a basket case, and 
have been slowly rebuilding it.  I have it transmitting and receiving OK 
now, but only when it's cold.

 From a cold start, the s-meter and receive function works as expected, 
with good meter swings on signal peaks.  However, as the rig heats up, 
the s-meter deflects less and less until it basically remains 
stationary.  I also begin to lose receive sensitivity.  Compressed air 
blown at spots underneath the chassis doesn't seem t have any effect, 
nor does air applied to the air variables.  It just... dies out.

Short of just starting to shotgun everything, does anyone have any 
suggestions on where to start looking?

Thanks...

Jeff

WB3JIH