[Elecraft] K2 Transmitter and KAT2 failures

[Don Wilhelm]

Damon,

Now that you are concentrating on the K2 itself, you may want to examine 
T4 and the low pass filter area carefully.  In the LPF, count the turns 
on each toroid - count only the turns that pass through the center of 
the core.  If there is an extra turn on the toroids, the LPF cutoff 
frequency will be too low and may even be shunting a lot of your signal 
to ground.  Likewise, count the turns on T4 and compare that with the 
manual.  The ratio of turns is important to allow the PA transistors to 
see the correct impedance match.

73,
Don W3FPR

Damon - KC5CQW wrote:
>      Well I did it again, My last set of finals just fried! I was using my
> manual tuner on 20m at 2W.
> I think what's happening is the power spike is overloading the finals at the
> end of each transmission.
> Now I no longer believe the KAT2 is responsible since it was out of circuit.
> I have not been able to find any faults in the KAT2. It just seemed a likely
> candidate because thats when the failures would occur.
> I've now proven that theory incorrect. I must have a fault in the LPF or PA
> sections. To date, I have not been successful in locating the problem. 
>      It is long overdue for me to swallow my pride and send the K2 in for
> service. I think what hurts the most is knowing that it will be something
> simple like a bad solder joint. 
> I want to thank Don and the everyone else that has helped me to this point.
> In the 2 1/2 months i've owned this radio, I'm glad to say that at-least I
> did make one contact on the air! 
>
> 73, Damon KC5CQW
>
>
>
> Damon - KC5CQW wrote:
>   
>> Below is some of the text that I sent to Gary. 
>> Basically, if I use the KAT2 to tune my 40m attic dipole the PA finals
>> will short out. 
>> I haven't tryied to tune any other antennas because I don't want to pay
>> for any more PA kits ($18.50 'ish each time I tune up).  
>> Also, CW is un-usable above 80m and no CW output on 10m (SSB and "tune"
>> yield 8.5W)
>>
>> See text below...
>>
>> 73, Damon KC5CQW
>>
>> Copied text from support email:
>>
>> On 40m-10m when I release the CW key or mic PTT in CW mode, the moment it
>> is released I get a power spike resulting in a HiCur warning.
>> On 12m and 10m I have no output during key down; Only the power spike. (CW
>> only, SSB is fine)
>> If the tune button is activated, The radio will give about 11w Max on 12m
>> and 8.5w on 10m.
>> All other bands yield 12-15W max.
>>
>>
>> At the time of the last PA meltdown, I was able to tune my 40m dipole on
>> 80, 40 and 10m; It failed at 30m.
>> There seems to be no rhyme or reason as to when a failure will occur. It
>> has happened at different frequencies.
>> I am reluctant to use the KAT2 except in bypass from this point on. 
>> I don't seem to have any problems with my MFJ-969 Versa Tuner II. 
>>
>> During some KAT2 troubleshooting, I found that the voltage on pin 1 of U4
>> was about 2.5VDC (3-4V spec at 5W) with a leg of R6 lifted.
>> Perhaps I'm not having a mechanical short on the LC board. Maybe the
>> SWR/Power bridge is sending the wrong data.
>> If I tune up on 10m into my dummy load, the K2 reports a 2.1:1 SWR. My
>> MFJ-969 read 1.05:1
>>
>> The best I can tell, everything seems to be fine on the SSB modes. I can't
>> help but think however, if a problem in CW if occurring that I may have
>> some distortion on SSB.
>>
>>
>>
>>     
>
>
> -----
> Damon Wascom KC5CQW
> Elecraft K2 #:6351
> Build: 12/28/07-01/01/08
>
>
>