[Elecraft] [Fwd: K2 Serial # 654] - Q18 problem

[Paul Erickson]

I finally got around to troubleshooting my K2's 160 meter problem, and 
discovered that Q18 (J310) appears
to be temperature/frequency sensitive. When I first fire up the rig from 
being cold, that received signal on
160 is fine, but after a while it begins to fade. Touching it with my 
finger, or spraying it with cold spray
brings the audio back up. As you can see below, another local ham 
(VA7DB) is having a similar problem.
Also, if you tune higher in frequency, or switch to a higher band, the 
audio comes back. Has anyone else
encountered this?

Elecraft is sending me a couple of replacements, but Dave and I are 
wondering what would cause the jfet
to go bad, in his case. In mine, the problem has been there from the get go.

Any thoughts will be greatly appreciated.

-- 
cheers, Paul - VA7NT (ex VE7CQK) - email: paule@sfu.ca

"Those who hear not the music, think the dancers mad..."

Hi Paul,

            Well, the problem on my K2 is that the 160 module was when 
installed approx a year ago working well,  as I have no antenna for that 
band I haven't used it.

 

Current symptoms are as follows:

 

1/    No receive signal when antenna connected to ant1 or ant 2    
regardless of setting on front panel,  however when antenna connected to 
RX only jack there is good receive signal.

 

2/    After some few moments the rx signal level drops to zero (even on 
the rx only ant jack)     Touching Q18 effects the signal,  IE, if one 
cools Q18 the signal levels return to normal if one warms it, they drop 
immediately to zero, the soldering is good and the transistor appears to 
be microphonic.

 

I would suspect the transistor being faulty but as your rig exhibited 
exactly similar results I'm thinking it may be systemic or possibly a 
bad batch of JFET's  (J310)??       

 

I have checked and re-seated all connectors and found the SSB board long 
connector strip to be oxidized a tad causing weird intermittent 
microphonic and other audio filter effects, a few iterations of plugging 
in and out again cured this problem.

 

The receive signal is still dead on the ant1 or ant2 jacks and still 
appears temperature /frequency sensitive on Q18 on 160 mtr band only,   
I'd be interested to see if any other rigs on the Elecraft reflector of 
similar vintage have exhibited similar problems.

 

As a point of interest the 160 mtr transmit signal is fine and has had 
C153 value changed to 68pf and R4 removed.

 

                                                               Dave  
VA7DB (Ex VE7PCC)