[Elecraft] K1 TX output low on 2 of 4 bands

[David Ek]

Mike, I didn't have the K1 internal ATU switched out like I thought I 
did. All is well (except for my embarrassment...).

73, Dave NK0E

On 7/5/2013 8:57 AM, Mike Morrow wrote:
> Dave/NK0E wrote:
>
>> My K1 (#1066, built 11 years ago) is a four-bander with ATU and internal
>> battery pack.
> What power supply were you using when you measured the output power
> that you report below?
>
>> In May I built an Elecraft W1 wattmeter and used it to discover that my
>> TX output (When "Out" in the menu is set to 7.0W) is only 1.2W on 15
>> meters. At that time, all other bands showed an output of 5W.
>>
>> However, last night, after an afternoon of using my K1 while fruitlessly
>> trying to tune up a new antenna, I noticed that the output on 20 meters
>> was also now down, measuring 1.5W.
>> I strongly suspect that a component failed due to TX'ing into high
>> SWR while trying to adjust the antenna I was working on.
> This is extremely unlikely.  Any RF board component failure would affect
> all four bands, not just 20m and 15m.  During use of a very poor antenna
> load, the most common result is shorting of the RF board D19 Zener that
> is across the RF-Q7 PA transistor, which is what D19 is designed to do to
> protect RF-Q7 (and usually destroy itself in the process).  This definitely
> has NOT happened to your K1.  Rest assured then that nothing was hurt
> on your K1 during your antenna tuning efforts.
>
> When some bands still function well, but others do not, it is a certainty
> that the problem is on the filter board.
>
> You have an older K1, and possibly an early KFL1-4 filter board.  The
> 16 trimmer capacitors that are on the KFL1-4 were originally white-body
> capacitors that were very prone to spontaneously changing their effective
> value.  A couple of years after the KFL1-4 was introduced, Elecraft changed
> all 16 trimmers to a much more stable design with a light blue body.
>
> Look at the four rows of trimmer capacitors on your KFL1-4, which are
> easily observed from the back of the K1 even without removing the KAT1.
> If they they do not have light blue plastic bodies, then you have the
> old troublesome original trimmers in place.  You'll need to get the
> replacement trimmers and install them.  Those are almost certainly
> the source of your problems.
>
> OTOH, if you have the newer blue-body trimmers, you will still want
> to re-align your KFL1-4 to restore full output.  In fact, you'll
> want to do that if you have white trimmers, just to verify that
> output can be restored in the interim before change out.
>
> When I still had those old trimmers on mine, I needed to re-peak 15m
> and 20m on my KFL1-4 every few months due to the drop in output power
> I observed.  So did a lot of other people.  After such results, Elecraft
> supplied a set of 16 blue-body replacements.  It was *not* a lot of fun
> removing 16 trimmers and replacing them, but it was worth it.  I
> recently re-peaked my KFL1-4 after more than eight years since last
> performed, and found essentially no pre-peaking degradation.
>
> 73,
> Mike / KK5F