internal ATU works fine on all but one band


Russ WQ0N
 

I have been having trouble with the internal tuner on 17M.  To investigate I attached a dummy load to my K3s and pressed the ATU button to tune near the center of each band.  The match came back to 1.0 or 1.1 to 1 on all bands except 17M.  I also hit the button two times within 5 sec, but it still did not find a match.  The relays click, but in the end, just two dashes on the display.  I am not sure if there is any setting that can cause this, or if there is a failed part on the ATU board.  Any advice would be appreciated.
Russ WQ0N


Keith_WE6R
 

It may not have enough power to find a tune match.

Try a manual tx gain cal on 17 meters;
Go to your favorite freq on 17m,
Set TUN PWR to "nor", set radio to EXACTLY 5.0 watts
Then long press XMIT to do a TUNE (send a carrier) for several seconds. 
If it does not throw an error, try your ATU tune now. If OK, then you are done!

If you get an err txg, then the radio is not making good power;
Could be the LPA  (Low power amp, 10watt board), but this would affect all bands.
Does it make ~11 watts on all bands when set to 11 watts? (and send carrier).

It could be the band pass filter is out of tune, or has a bad tweaker capacitor. That can limit RF output.
Put a dummy load on the KXV3 xvtr OUT BNC, and run the MW gain cal with the K3 utility to see if that fails on 17m.
Keith WE6R Elecraft K3/K4 Tech.


Russ WQ0N
 

Hi Keith,
Thanks for the guidance!  Using a dummy load, with the ATU bypassed, the manual tune on 17M came back with ERR TXG.  It also indicated only 4.4W.  I repeated the same procedure on several other bands, the power level went to 5.0W and did not show the error when the tune was stopped.  I then tested at 11 watts (by using my keyer to send the carrier) again the power level displayed was 4.4W on 17M and 11W on the other bands that I tested.  I am in search of a BNC connection to my dummy load to try your final suggestion of MW gain cal.
1) Does this info give you a better picture of what is going on?
2) I realize that if there is a bad component, the radio will need to be sent to you for repair; but if there is an "out of tune" band pass filter, is that correctable by me, or does it also require board level adjusting, best done by you guys?  
Russ WQ0N


Keith_WE6R
 

Hi Russ; Sounds like the BPF. If it is an older radio with blue tweaker caps, we usually replace them all. But you probably could attempt tuning 17m with out sweeping it with a spectrum analyzer as it is a narrow band. The old blue ones can get flakey, so just barely wiggle the two and while transmitting. Set for 11 watts and see if you can restore power.
If they seize up they will have to be replaced. 17m is paired with 15m so make sure power is good there too before buttoning it up.
Keith WE6R K3/K4 Tech


Russ WQ0N
 

Hi Keith,  I located the necessary cable and performed both the Low Power Transmitter Gain Calibration and the 1 Milliwatt gain Calibration.  Both failed when they got to the 17M band.  the LP "settled at 4.8 W",  the MW "settled at 0.19 MW".  I have submitted a Tech Support Form, but I am also interested in attempting to "wiggle" the caps you suggested.  Can you tell me specifically where to locate them?  I have downloaded the K3s assembly manual which includes board images, but feel free to offer other another way to identify the caps.  Thanks again for your help!  - Russ WQ0N


Keith_WE6R
 

There are a bunch of adjustable caps, they are marked on the board 17m, C136 & C149.
Keith