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

[Fred Moore]

Sorry for the late response..  I had the exact problem several weeks
ago.  Every time I removed the batteries the problem would be
resolved..  The problem was ultimately me being a dumb ass..  I had
purchased a nice blue tooth speaker that perfectly sat on top of the
KX3, however it kept sliding off.  My solution was to glue a small round
magnet on the front corners on the KX3 top.  I also glued the same small
magnet on the bottom of the radio.  Well guess what, I knew better but
didn't even think about magnetic shielding of the inductors in the ATU. 
While testing everything was fine, when I was convinced everything was
ok I would place the radio back in it's operating position everything
was still ok even with speaker on top, as long as I was on 20 meters, as
soon as I went to 40 which could be a couple of days later.. the radio
again went to 25.4:1  

One magnet was not enough to do it, but when both magnets were on the
top right hand corner, it was all over for the ATU.. makes 100% sense
now that I know what was happening...   Regards.. Fred

Fred Moore
email: fred at fmeco.com
       fred at safes.com
phone:  321-217-8699

On 4/19/17 11:55 PM, nate t wrote:
> Hi all,
>
> I opened up the KX3 and pulled the ATU, everything seemed to be in order and the LPF was in the correct position. 
>
> I put the original batteries back in to keep the testing the same as previously. They were a bit lower than I had previously thought, read 9V (alkaline). I put up a 20m dipole and tested it, 20m tuned up right away and I let it run for a bit. I then switched down to 40m and it tuned up right away to a 1.0:1. After switching back and forth between 40/30/20 a few times, I noticed that the relays seemed to be switching a bit slower than normal, and that the tuning power was going down to 2.0W instead of the normal 3.0W. 
>
> Went to 40m again, and it started landing on the 25.4:1 SWR every try. Pulled up the battery monitor on the display, and while it was running the tuning process, the voltage was dropping down to 7.9V, and it'd stick at 25.4:1. Switched over to external power and it would properly tune 40m again on the 20m dipole without issue. 
>
> The dummy load I ordered arrived today as well, and using new batteries, it will tune 1:0.1 on all bands. 
>
> I'm going to chalk this up to being a low voltage situation, and hopefully it doesn't return!
>
> I appreciate everyone's suggestions.
>
> 73
>
>
>> On Apr 17, 2017, at 11:35 AM, Walter Underwood <wunder at wunderwood.org> wrote:
>>
>> 25.4:1 SWR is what the KX3 reads for a short or an open, if I remember correctly.
>>
>> Agreed, open it up, make sure everything is tight, include the ribbon cable.
>>
>> wunder
>> K6WRU
>> Walter Underwood
>> CM87wj
>> http://observer.wunderwood.org/ (my blog)
>>
>>> On Apr 17, 2017, at 11:20 AM, Don Wilhelm <donwilh at embarqmail.com> wrote:
>>>
>>> Nate,
>>>
>>> Since the problem is intermittent, I would not suspect a problem with an active component.
>>>
>>> You might want to remove the bottom cover and check to be certain the hardware on the BNC jack is tight and the LPF on the BNC connector is properly positioned.  You may have to lift the KXAT3 to check - see Figure 43 of the KX3 Kit Assembly Manual.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>> On 4/16/2017 4:55 AM, nate t wrote:
>>>> 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.
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