Posted by
omehegan on
Oct 05, 2010; 6:38am
URL: http://elecraft.85.s1.nabble.com/K2-Debugging-low-transmit-power-tp5601987.html
Hello -
Two nights ago I completed the assembly of my K2's RF board, and after
a visual inspection verification of resistance checks, I assembled the
radio per the instructions and began the third phase of alignment and
test. I've discovered a problem right off the bat, though. In the 40
meter transmitter alignment section, when I put the K2 into tune mode
at 2 watts power, I'm only reading .3-.4 watts on the onboard
wattmeter (it alternates between the two). This is with a connection
to a 100W dummy load. Varying L1 and L2 has no effect on the power
reading.
I discovered one mistake: I misread the instructions for winding T4's
5-6 and 7-8 windings. I wound these bare wires through BOTH holes in
the core, in a U shape, thus connecting 6-7 and 5-8 (and very possibly
all 4 together with a short in the middle - this is what comes of
staying up too late working on a project!). I corrected this mistake
tonight, but I'm seeing no change on the measured power. Is it
possible that this mistake fried something? I never saw any smoke or
smelled burned silicon, and the thermal pads on Q7 and Q8 look normal.
I have also noticed that if I vary the power adjustment on the front
panel while in tune mode, I see no change on the wattmeter. That seems
significant.
These are the other checks I've done so far, per the troubleshooting
instructions:
* As far as I can tell, my current limit is set to 2.5A. I have not
seen any "high current" warnings.
* I am using a dummy load to test, I do not currently have an antenna
set up that I can use. I have tried two coax jumpers for the dummy
load, both test OK on continuity. No change on power output.
* The bottom cover is correctly installed and there are no shorts to
it that I can see.
* I checked all component values in the RF detector, they are correct.
* I examined transformers T1-T4, all appear to be wound and wired
correctly.
* I checked R50, it is measuring the correct resistance.
* I checked for hot components and found none.
* I checked visually, but not yet with a DMM, for shorts and opens.
I have NOT yet done the following:
* Looked for shorts in the LPF or BPF - visual inspection shows
nothing unusual. How exactly would I check this section with a DMM?
* Checked DC voltages in the transmitter and ALC circuitry - I will
need to re-assemble the K2 somewhat before I can do this.
* Used the RF probe to trace signal flow.
Any further suggestions at this point would be greatly appreciated. I
can get access to an oscilloscope if that would be useful. Suggestions
of the "check x for voltage/resistance y" would be most helpful
(though I realize there is a voltage table in the manual that I need
to go through).
Many thanks in advance!
--
[hidden email] (Owen B. Mehegan)
'You write the lie
You'd like to be
When your life looks like a book you wouldn't read'
--Blake Schwarzenbach
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