[Elecraft] K2 Lo P

[Jay Sissom]

Too late. :)  I noticed that two of the leads of T1 crossed over each
other under T1 and above the circuit board.  They were tinned all the
way to the toroid so it looked like they might have been shorted.   I
lifted the toroid a bit off the board and checked and got SWR of 1 to
1 on all bands.   The tuner worked for a while when he first got the
radio so this could be the cause of the somewhat intermittent problem.

I attempted to remove T1 to fix the crossed wire.  Unfortunately, the
person who built this folded each lead at a 90 degree angle under the
circuit board which made it extremely difficult to remove it and I had
to destroy T1 to remove it.  I rebuilt it and reinstalled it and now
in CALn, I only get Hi no matter the position of C55.  So I'm taking a
break and will get back at it.

I measured the resistance between the 4 leads out of the many turns
side of T1 and got 0 ohms like I should.  So it seems it is connected
OK. Thanks again for your help.  I'll look into it again later today.

Thanks & 73
Jay
W9IUF


On Sun, Jun 21, 2009 at 12:41 PM, Don Wilhelm<don at w3fpr.com> wrote:
> Jay,
>
> Don't tear into it too quickly.  Make some methodical tests first.
>
> TRUISM:
> If you successfully obtained a null while connected to a dummy load, and
> then left that same dummy load connected when you checked the SWR reading,
> the SWR will read 1.0 - if it does not, your null was not correct.
> End of truism.
>
> An SWR of 9.9 usually indicates either a short or an open circuit - 9.9 is
> the highest SWR that is indicated by the K2.  Be certain the coax cable to
> your dummy load is good as a first step.
> You could not have achieved a proper null if you have either an open circuit
> or a short condition, so you will have to do the null again.
>
> Before doing anything else, make a couple of 'sanity' measurements.
> Set the ATU menu to CALP and set to ANT1, then power off and remove the
> input coax to the KAT2 from the RF Board.
> Measure the resistance from the input coax center conductor to the center
> conductor of the ANT1 jack - it should measure zero ohms.  Also measure
> resistance from the center conductor of the ANT1 jack to the shell - that
> should be very high (even infinite).  If these measurements do not check out
> properly, the path is not intact through the wattmeter and relays K17 and
> K18 and that problem must be found before proceeding.
>
> If the above checks were good, then connect the dummy load to ANT1 and
> measure the resistance from the center conductor to the shield on the input
> coax (with the input coax still unplugged) - it should measure 50 ohms.  If
> not, stop and find the problem.
>
> If all is well down to here, then put the KAT2 input coax back in place and
> try the null again.  If it anywhere near normal, the slot on C55 will be
> within 30 degrees of parallel with the long side of the KAT2 board.  If it
> is perpendicular to the long side of the board, then the capacitor is either
> at its minimum or maximum capacity point and you have a problem with T1, R3,
> R4, C54 or C55.  As usual, T1 is the most likely suspect.
>
> 73,
> Don W3FPR
>
>
>
> Jay Sissom wrote:
>>
>> Oops, I sent this to Don by himself, but thought I should send it to
>> the list just in case it helps someone.
>>
>>
>>
>> Thanks Don, just an update. I re-nulled C55 and it nulled fine.  When
>> I checked the voltage at U4 pin 1, it was 2.8V which was a little low.
>>  Then I set R1 & R2.  After doing that, the SWR into a dummy load is
>> 1:9.9.  I'll take the antenna tuner apart and look to see what I can
>> find.
>>
>> Thanks & 73
>> Jay
>> W9IUF
>>
>> On Sat, Jun 20, 2009 at 12:46 AM, Don Wilhelm<w3fpr at embarqmail.com> wrote:
>>
>>>
>>> Jay,
>>>
>>> It really sounds as though you have a problem with the wattmeter in the
>>> KAT2.
>>> Try balancing and calibrating the wattmeter again.  If you cannot achieve
>>> a
>>> good null with a good 50 ohm non-reactive dummy load, check T1 and its
>>> associated components (T1 for well tinned and soldered leads and C34, R3,
>>> R4, D1 and D2 for god soldering and proper orientation).
>>>
>>> If you cannot achieve a good null when balancing the wattmeter, stop and
>>> ask
>>> for specific help.  The null is a pre-requisite to proper calibration.
>>>
>>> 73,
>>> Don W3FPR
>>>
>>
>