Posted by
omehegan on
Oct 06, 2010; 5:42am
URL: http://elecraft.85.s1.nabble.com/K2-Debugging-low-transmit-power-tp5601987p5605856.html
Thanks again for the suggestions Don. Tonight I started doing some
signal tracing, and my RF probe seems to work fine with my DMM.
However, I ran up against a different obstacle: I don't have a signal
generator handy, and the LPF/BPF/T-R Switch tests seem to require one.
I can get access to one but it won't be until tomorrow at least.
I did find one other data point for my symptoms. On SOME bands, I get
the expected power out when I put the K2 into tune mode. Here are the
results of my tests:
80m sometimes shows "high cur" the first time I test, then I quickly
turn off tune, then try again and I see a normal reading
40m always too low
30m same as 80m
20m OK
17m OK
15m OK
12m too low
10m too low
I checked continuity on all my toroids, from "pad to pad" instead of
lead to lead, as far as I was able. Everything seems to check out
there. I'm not sure I can do anything else without a signal generator,
but I'm open to suggestions.
--
[hidden email] (Owen B. Mehegan)
'This above all: to thine own self be true,
And it must follow, as the night the day,
Thou canst not then be false to any man.'
--William Shakespeare
On Oct 5, 2010, at 7:01 AM, Don Wilhelm wrote:
> Owen,
>
> I am going to assume that you were successful with the Alignmant and
> Test Part II and were able to receive 40 meter signals. If not, you
> need to backtrack a bit and get receive working first.
>
> The easiest way to troubleshoot a "lack of power output" problem is
> to do Transmit Signal Tracing. You can use an RF Probe or an
> oscilloscope with a 10X probe.
>
> Turn the manual to the Appendix E section titled Transmit Signal
> Tracing and begin there. If using an RF Probe, the correct expected
> values are listed, but if using an oscilloscope, multiply those
> values by 2.8 and observe the peak to peak voltage of the RF waveform.
>
> An important note - the K2 will normally increase drive in an
> attempt to increase the power output if the voltage out of the RF
> detector is too small. What that means is that all RF voltages
> prior to the failing stage the RF voltages will be higher than the
> listed expected values. You will be investigating the transmit
> chain in the order listed (do not skip around), searching for the
> *first* stage where the output is lower than expected - that is the
> failing stage which then needs to be analyzed to determine why it is
> not operating properly. Measurements beyond this first failure
> point are not relevant to that first problem to be found.
> All RF Voltage measurements in the list can be done from the top of
> the RF Board. Do not transmit with the heat sink removed. If the
> PA transistors do get a bit of drive, will produce output and if the
> heat sink is not in place, they will quickly overheat and fry
> themselves.
>
> Normal failures are soldering problems, toroid leads or incorrectly
> placed components. Active device failures are way down of the list
> of failure suspects unless something has caused it to be abused.
>
> 73,
> Don W3FPR
>
> On 10/5/2010 2:38 AM, Owen B. Mehegan wrote:
>> 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:
>>
>
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