http://elecraft.85.s1.nabble.com/K2-Debugging-low-transmit-power-tp5601987p5605213.html
To: "Owen B. Mehegan" <
> 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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