[Elecraft] KX3 tuner getting stuck at 25.4:1 SWR

[nate t]

Hi,

I was working with my KX3 earlier today, RX only, using an endfed, while running on batteries, RXing WSPR and PSK31. 

After running for a bit, the ATU seemed to stop working. Attempting to retune on 40m, it would stick at a 25.4:1 SWR. 

Tried switching down to 20m and it retuned right away to a 1.3:1. Applying external power to the unit, I tried tuning again on 40m (battery was reporting 10V if I recall correctly); It then tuned the end fed up, but only to a 1.7, which it will typically match to a 1.0:1, it would also get stuck at the 25.4:1 SWR on some of the attempted tunes.

Trying another dipole I have (10m), and with external power, it will tune up 30m, 20, 10m to a good SWR (1.0 or 1.2 :1), but on 40m, it will either tune to ~1.7 - 3:1 (expected), or it falls back onto the 25.4:1. 

When the relays are running through the tuning procedure, I'm noticing that for about half the time the relays are clicking, it's showing a 25.4:1 SWR. What I mean by this is that it seems for all the possible tuning combinations/paths in the tuner used on 40m, there is a fault some where leading to the 25.4:1 SWR for many of the paths/combinations.

Found this old mailing list post [1] which the resolution was to have it sent in for repair, which replaced Q2/Q7.

I'm wondering if anyone has a suggestion on testing or this issue. I don't have a dummy load to test with at the moment, but have one on order. Should I suspect it is an issue with the ATU or more likely Q2/Q7? It would most likely be cheaper/faster to replace the ATU, but I'm guessing it's more likely that it will need to be sent in for repair, and the ATU is fine. Any insight is appreciated. 


Regards,
Nate

[1] - http://elecraft.365791.n2.nabble.com/Re-KX3-tuner-td7600743.html