Greetings - My K3 has had low output for quite some time, maybe 60-90w depending on the band. I always meant to look into it and fix it someday. Now it has no RF output at all. (Just in time for VK0 and FT/J!) I believe I have traced the problem to two transistors on the LPA board (driver stages), Q4 and Q5, but am not confident they are the only parts at fault. I'm hoping someone else has had the same problem and found the solution.
I tried re-seating all the connectors, with a drop of DeoxIt on the pins, and running TX gain cal. 5w and 50w failed immediately, but 100 mW is OK on all bands. KPA-100 was removed, the PA jumper installed between P67A & P67B, and the config menu was set to KPA not installed. Measurements were taken with an old Tek 2465. DC voltages are all correct. Measuring with a scope - I get a nice clean sine wave going in to the LPA board at P71A pin 3. Most bands are 1.2 to 2.2v P-P, but 6m is only 0.6v. The output of Q1 is a little distorted. The output of Q2 varies from 10-25v, depending on the band, and is also a little distorted. Signals at the base of Q4 and Q5 are back down to 3v. Output of Q4 and Q5 is a few mV. Changing the drive control has no affect on signal levels. Is 1 to 2 v P-P the correct drive level at P71A? What is an acceptable variation in power level between different bands? Should the drive control change signal levels here, or does that happen later in the circuit? I am also concerned about the distortion on the wave forms. Q4 and Q5 are available from RF Parts for $5 apiece, so replacing them will likely be my next stap. Thank you. -- 73, Mike Cizek WØVTT ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com