I did some signal tracing to try to find the problem with my new K2. The rig
works fine on most bands, with low output on the higher bands (5W on 15m, 3 or
4W on 10m)) and almost none on 12m.
There seem to be two problems: one is variable power output and the other
is low output on the high bands. Taking the variable output first:
On Tune, the power output is often much higher than specified by Power Out.
This seems to occur about 1 in 3 or more times when Tune is pressed
continuously. Seven watts for five, for example. The K2 does not bring this
higher voltage down, it stays there or runs up ward ar watt or so. I checked
pin 2 of U8 and it is always 5V, key down or not. It should be 0.7 to 2.5V in
Tune. All components seem OK in this area and the RF detector area. Tests 1 to
5 on p.14 of Xmit mixer output, Buffer Output, Band Bass Filter output and TR
switch output all reflect this intermittent variation when measured several
times in a row.
The next few tests in TX signal tracing (p.14 in Troubleshooting appendix)
are stable with no variation when consecutive measurements are made, and near
expected values for Pre-driver output (0.116V instead of 0.12), Driver input
(0.33 instead of 0.26V), Driver output (1.74 instead of 1.8V), PA Q7 input
(0.43 instead of 0.38V) and Q8 (0.50 instead of .38V) and RF Detector input
(2.09 instead of 2.0V).
The PA Transistor tests (Item 7 on the list) are fairly far off the
expected values. With the positive probe on the base of Q7 and Q8, the
Collector reading was 4400 ohms instead of 600 and the Emitter 2700 instead of
600. With the negative probe, they were 6300 instead of 1300 and 2700 instead
of 3000+.
Page 4 schematic components look OK, as do other ones involved. Since the
Receiver signal tracing requires a signal generator set at 1.4mV, I could not
do those checks.
I will set the low output problem aside for now, although it may have
something to do with the situation.
Elecraft will call me back when they are free and no doubt they will cure
my ills. But in case someone has similar problem someday (or has gone through
this one and can help), I thought I would post my results so far. I've found
that hese voltage checks are a lot easier than I thought they would be.
Bob VA3RKM
_______________________________________________
Elecraft mailing list
Post to: Elecraft@mailman.qth.net
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.):
http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com
