[Elecraft] New K2 with 5W problem Now Almost Fixed

Sun Jun 2 17:25:07 2002

> Ron, AC7AC instantly fixed the low or no output on the two bands (20 and
17
> meters). Spinning the caps did the trick.

I'm glad it worked. That problem has been known for at least two years now.
If it wasn't in the book, then the Elecraft guys ARE running well behind in
their documentation <G>.

> Another person has a similar problem with Tune going into high current for
no
> apparent reason, turning back to rx, Tuning again and appears normal. Do
> others have that same problem?

Keep in mind, Jeff, that the automatic power control circuit is disabled in
TUNE. The power control system doesn't reset the output level until you get
out of TUNE, then go back into TUNE.

I can't quite picture what is happening in the case you describe, but I'd be
suspicious that it is "normal" behavior when the power control circuit is
disabled. The symptom will probably go away when you fix the overcurrent
problem. You ARE drawing a LOT of current at 5 watts, as you say. (I run
about 1.5 - 1.6 amps at 5 watts).

The Power Control is disabled on purpose in TUNE so the K2 won't be moving
the power output all over the place while you adjust an ATU. That would make
your readings on an SWR meter look strange. It is probably needed to keep
from confusing the KAT2 as well.

Another oddity in the Power Control that lot of new K2 owners "discover" is
that in normal operation it does NOT change the power output until you
transmit again. That is, the Power Control circuit measures the r-f voltage
at the antenna jack, then adjusts the power out to produce the voltage that
would equal the requested power set by the POWER knob. It assumes that the
rig is connected to a 50 ohm non-reactive load. That's why you were asked if
you were connected to a good dummy load.

So, if  you turn up with the power down near minimum, then turn up the power
to 10 watts and hit the key you will not see 10 watts output immediately.
The K2 has to transmit, note that the power is still too low, then bring it
up to what you are requesting with the POWER knob. Sometimes it takes
sending a couple of "dits" or a long "dah" to make it react after changing
the POWER setting.

It's a good idea to think of the POWER control as a POWER "request" control,
not what actually sets the power. The K2 does that automatically when you
transmit.

As for your overcurrent issue, did you double check the number of turns on
the 40 meter low pass filter toroids L25, L26 and double check the value of
the caps C225 and C227  (470 pf),  and C226 (820 pf)?

Also check very carefully for PTTL (Poorly Tinned Toroid Leads) or anything
that would leave you with an open circuit at L25 or L26. PTTL is very hard
to spot in many cases. The solder will flow very nicely around the enamel
and look like a good joint while the wire is still insulated from the pad.

Ron AC7AC

> _______________________________________________
> Elecraft mailing list: [email protected]
> You must be a list member to post to the list.
> Postings must be plain text (no HTML or attachments).
> See: http://mailman.qth.net/mailman/listinfo/elecraft
> Elecraft Web Page: http://www.elecraft.com
>